# How can we use hypervelocity stars to determine the origins of the Universe?

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I was reading this article finding evidence of Universe's origin, which describes that in 1 trillion years we may lose the ability to determine how the universe was created.

The answer seems to be using hypervelocity stars. These are stars that have been ejected from their galaxy. Using the expansion of the universe, we can use the velocity of the star to then determine evidence of the Big Bang. But how does this work? Is there calculations we can do now that agree with our understanding of the universe and its age when working with hypervelocity stars?

I understand finding a hypervelocity star is very hard to do. I guess my thought here is that astronomers have modeled this scenario and found that if we were to find a hypervelocity star, we could then use the scenario above to calculate the age. I'm assuming the age calculated agrees with current estimates.

How can we use hypervelocity stars to determine the origins of the Universe?

First and foremost, I should clear something up: our knowledge of the Big Bang is incredibly limited, and so we don't even know the origins of the Universe today. General relativity and quantum mechanics both break down as you get closer and closer to $t_0=0$. All we really know is that something happened 13.8 billion years ago. However, if we look at the expanding universe, we can extrapolate that, 13.8 billion years ago, space was much less dilated than it is now.

General relativity suggests that the Universe would be packed into a singularity. This is not a good approach, since GR can't properly explain such conditions (QM is more fit to do so, but that alone can't explain how gravity acted), so we really haven't the slightest clue as to what happened 13.8 billion years ago. That said, we still know when the Big Bang (whatever it may have been) occurred, and that's what future astronomers may be able to find out.

The idea the article brings up is this: by one trillion years from now, the expansion of space will have driven away any other galaxies from our line of view, and CMB radiation will have become too redshifted to be detectable.

However, hypervelocity stars will likely be detected outside of the Milky Way (or rather, Milkomeda). Once these stars get far enough from the Milkomeda's gravitational influence, we can observe their acceleration due to the expansion of space, just as we do for many galaxies today. The 4-page paper the article is based on, Loeb (2011), actually makes this clear in a graph:

As the stars get farther and farther from Milkomeda, the gravity's pull on the stars will weaken and they will be accelerated by the expansion of space. This will really become noticeable once they are about 2.3 megaparsecs from the galaxy. Of course, these stars will not be easily found, but Loeb mentions that future astronomers will likely have advanced their tools and instruments by that time.

Loeb explains that, once we observe their redshifts as their distances increase, we can confirm Hubble's law. After this, we just need to measure the necessary parameters, and finally we can calculate the age of the Universe using the Friedmann equation: $$t_0 = frac{1}{H_0} F(Omega_r,Omega_m,Omega_Lambda,dots)$$

That's the gist of it. The hypervelocity stars will be the only extragalactic objects detectable by then, and thus we will rely on them to confirm our measurements.

Interestingly, Loeb mentions that observing and analyzing the expansion of the Universe at that time would answer some of the uncertainties we have today:

The working assumption so far was that the vacuum energy density remains constant and does not decay to a lower energy state over hundreds of e-folding times. Measuring the dynamics of hypervelocity stars at late cosmic times provides the added benefit of testing whether the cosmological constant is truely [sic] constant. Indications to the contrary might reveal new physics, such as that considered by evolving dark energy models.

Thus, even though much of the Universe will not be observable by that time, we will ironically have more answers about cosmology than we do today, simply by observing the few extragalactic objects that will be visible.

This is the general explanation of how we can find the time since the Big Bang. Remember that even now, we really have no idea about the origins of the Universe - it's a major unsolved problem in physics. All we know is something happened 13.8 billion years ago. Using hypervelocity stars, future humans would be able to determine the time since the Big Bang as well. Don't get your hopes up on humans surviving for 1 trillion years, though.

## Chinese Astronomers Spot Two New Hypervelocity Stars

Most stars in our galaxy behave predictably, orbiting around the center of the Milky Way at speeds of about 100 km/s (62 mi/s). But some stars achieve velocities that are significantly greater, to the point that they are even able to escape the gravitational pull of the galaxy. These are known as hypervelocity stars (HVS), a rare type of star that is believed to be the result of interactions with a supermassive black hole (SMBH).

The existence of HVS is something that astronomers first theorized in the late 1980s, and only 20 have been identified so far. But thanks to a new study by a team of Chinese astronomers, two new hypervelocity stars have been added to that list. These stars, which have been designated LAMOST-HVS2 and LAMOST-HVS3, travel at speeds of up to 1,000 km/s (620 mi/s) and are thought to have originated in the center of our galaxy.

The study which describes the team’s findings, titled “Discovery of Two New Hypervelocity Stars From the LAMOST Spectroscopic Surveys“, recently appeared online. Led by Yang Huang of the South-Western Institute for Astronomy Research at Yunnan University in Kunming, China, the team relied on data from Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) to detect these two new hypervelocity stars.

Astronomers estimates that only 1000 HVS exist within the Milky Way. Given that there are as many as 200 billion stars in our galaxy, that’s just 0.0000005 % of the galactic population. While these stars are thought to originate in the center of our galaxy – supposedly as a result of interaction with our SMBH, Sagittarius A* – they manage to travel pretty far, sometimes even escaping our galaxy altogether.

It is for this very reason that astronomers are so interested in HVS. Given their speed, and the vast distances they can cover, tracking them and creating a database of their movements could provide constraints on the shape of the dark matter halo of our galaxy. Hence why Dr. Huang and his colleagues began sifting through LAMOST data to find evidence of new HVS.

Located in Hebei Province, northwestern China, the LAMOST observatory is operated by the Chinese Academy of Sciences. Over the course of five years, this observatory conducted a spectroscopic survey of 10 million stars in the Milky Way, as well as millions of galaxies. In June of 2017, LAMOST released its third Data Release (DR3), which included spectra obtained during the pilot survey and its first three years’ of regular surveys.

Containing high-quality spectra of 4.66 million stars and the stellar parameters of an additional 3.17 million, DR3 is currently the largest public spectral set and stellar parameter catalogue in the world. Already, LAMOST data had been used to identify one hypervelocity star, a B1IV/V-type (main sequence blue subgiant/subdwarf) star that was 11 Solar Masses, 13490 times as bright as our Sun, and had an effective temperature of 26,000 K (25,727 °C 46,340 °F).

Artist’s impression of hypervelocity stars (HVSs) speeding through the Galaxy. Credit: ESA

This HVS was designated LAMOST-HSV1, in honor of the observatory. After detecting two new HVSs in the LAMOST data, these stars were designated as LAMOST-HSV2 and LAMOST-HSV3. Interestingly enough, these newly-discovered HVSs are also main sequence blue subdwarfs – or a B2V-type and B7V-type star, respectively.

Whereas HSV2 is 7.3 Solar Masses, is 2399 times as luminous as our Sun, and has an effective temperature of 20,600 K (20,327 °C 36,620 °F), HSV3 is 3.9 Solar Masses, is 309 times as luminous as the Sun, and has an effective temperature of 14,000 K (24,740 °C 44,564 °F). The researchers also considered the possible origins of all three HVSs based on their spatial positions and flight times.

In addition to considering that they originated in the center of the Milky Way, they also consider alternate possibilities. As they state in their study:

“The three HVSs are all spatially associated with known young stellar structures near the GC, which supports a GC origin for them. However, two of them, i.e. LAMOST-HVS1 and 2, have life times smaller than their flight times, indicating that they do not have enough time to travel from the GC to the current positions unless they are blue stragglers (as in the case of HVS HE 0437-5439). The third one (LAMOST-HVS3) has a life time larger than its flight time and thus does not have this problem.

In other words, the origins of these stars is still something of a mystery. Beyond the idea that they were sped up by interacting with the SMBH at the center of our galaxy, the team also considered other possibilities that have suggested over the years.

Artist’s impression of the ESA’s Gaia spacecraft, looking into the heart of the Milky Way Galaxy. Credit: ESA/ATG medialab/ESO/S. Brunier

As they state in these study, these “include the tidal debris of an accreted and disrupted dwarf galaxy (Abadi et al. 2009), the surviving companion stars of Type Ia supernova (SNe Ia) explosions (Wang & Han 2009), the result of dynamical interaction between multiple stars (e.g, Gvaramadze et al. 2009), and the runaways ejected from the Large Magellanic Cloud (LMC), assuming that the latter hosts a MBH (Boubert et al. 2016).”

In the future, Huang and his colleagues indicate that their study will benefit from additional information that will be provided by the ESA’s Gaia mission, which they claim will shed additional light on how HVS behave and where they come from. As they state in their conclusions:

“The upcoming accurate proper motion measurements by Gaia should provide a direct constraint on their origins. Finally, we expect more HVSs to be discovered by the ongoing LAMOST spectroscopic surveys and thus to provide further constraint on the nature and ejection mechanisms of HVSs.”

## Determining the mass of the Milky Way using hypervelocity stars

An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA

For centuries, astronomers have been looking beyond our solar system to learn more about the Milky Way galaxy. And yet, there are still many things about it that elude us, such as knowing its precise mass. Determining this is important to understanding the history of galaxy formation and the evolution of our universe. As such, astronomers have attempted various techniques for measuring the true mass of the Milky Way.

So far, none of these methods have been particularly successful. However, a new study by a team of researchers from the Harvard-Smithsonian Center for Astrophysics proposed a new and interesting way to determine how much mass is in the Milky Way. By using hypervelocity stars (HVSs) that have been ejected from the center of the galaxy as a reference point, they claim that we can constrain the mass of our galaxy.

Their study, titled "Constraining Milky Way Mass with Hypervelocity Stars", was recently published in the journal Astronomy and Astrophysics. The study was produced by Dr. Giacomo Fragione, an astrophysicist at the University of Rome, and Professor Abraham Loeb – the Frank B. Baird, Jr. Professor of Science, the Chair of the Astronomy Department, and the Director of the Institute for Theory and Computation at Harvard University.

To be clear, determining the mass of the Milky Way galaxy is no simple task. On the one hand, observations are difficult because the solar system lies deep within the disk of the galaxy itself. But at the same time, there's also the mass of our galaxy's dark matter halo, which is difficult to measure since it is not "luminous", and therefore invisible to conventional methods of detection.

Stars speeding through the galaxy. Credit: ESA

Current estimates of the galaxy's total mass are based on the motions of tidal streamers of gas and globular clusters, which are both influenced by the gravitational mass of the galaxy. But so far, these measurements have produced mass estimates that range from one to several trillion solar-masses. As Professor Loeb explained to Universe Today via email, precisely measuring the mass of the Milky Way is of great importance to astronomers:

"The Milky Way provides a laboratory for testing the standard cosmological model. This model predicts that the number of satellite galaxies of the Milky Way depends sensitively on its mass. When comparing the predictions to the census of known satellite galaxies, it is essential to know the Milky Way mass. Moreover, the total mass calibrates the amount of invisible (dark) matter and sets the depth of the gravitational potential well and implies how fast should stars move for them to escape to intergalactic space."

For the sake of their study, Prof. Loeb and Dr. Fragione therefore chose to take a novel approach, which involved modeling the motions of HVSs to determine the mass of our galaxy. More than 20 HVSs have been discovered within our galaxy so far, which travel at speeds of up to 700 km/s (435 mi/s) and are located at distances of about 100 to 50,000 light-years from the galactic center.

These stars are thought to have been ejected from the center of our galaxy thanks to the interactions of binary stars with the supermassive black hole (SMBH) at the center of our galaxy – aka. Sagittarius A*. While their exact cause is still the subject of debate, the orbits of HVSs can be calculated since they are completely determined by the gravitational field of the galaxy.

Artist’s conception of a hyperveloctiy star heading out from a spiral galaxy (similar to the Milky Way) and moving into dark matter nearby. Credit: Ben Bromley, University of Utah

As they explain in their study, the researchers used the asymmetry in the radial velocity distribution of stars in the galactic halo to determine the galaxy's gravitational potential. The velocity of these halo stars is dependent on the potential escape speed of HVSs, provided that the time it takes for the HVSs to complete a single orbit is shorter than the lifetime of the halo stars.

From this, they were able to discriminate between different models for the Milky Way and the gravitational force it exerts. By adopting the nominal travel time of these observed HVSs – which they calculated to about 330 million years, about the same as the average lifetime of halo stars – they were able to derive gravitational estimates for the Milky Way which allowed for estimates on its overall mass.

"By calibrating the minimum speed of unbound stars, we find that the Milky Way mass is in the range of 1.2-1.9 trillions solar masses," said Loeb. While still subject to a range, this latest estimate is a significant improvement over previous estimates. What's more, these estimates are consistent our current cosmological models that attempt to account for all visible matter in the universe, as well as dark matter and dark energy – the Lambda-CDM model.

"The inferred Milky Way mass is in the range expected within the standard cosmological model," said Leob, "where the amount of dark matter is about five times larger than that of ordinary (luminous) matter."

Distribution of dark matter when the universe was about 3 billion years old, obtained from a numerical simulation of galaxy formation. Credit: VIRGO Consortium/Alexandre Amblard/ESA

Based on this breakdown, it can be said that normal matter in our galaxy – i.e. stars, planets, dust and gas – accounts for between 240 and 380 billion solar masses. So not only does this latest study provide more precise mass constraints for our galaxy, it could also help us to determine exactly how many star systems are out there – current estimates say that the Milky Way has between 200 to 400 billion stars and 100 billion planets.

Beyond that, this study is also significant to the study of cosmic formation and evolution. By placing more precise estimates on our galaxy's mass, ones which are consistent with the current breakdown of normal matter and dark matter, cosmologists will be able to construct more accurate accounts of how our universe came to be. One step closer to understanding the universe on the grandest of scales!

## Contents

"Total velocities in the Galactic rest frame are computed correcting radial velocities and proper motions for the solar and the local standard of rest (LSR) motion (Schönrich 2012). In doing so, we assume that the distance between the Sun and the [Galactic Center] GC is d = 8.2 kpc, and that the Sun has an height above the stellar disk of z = 25 pc (Bland-Hawthorn & Gerhard 2016). We assume a rotation velocity at the Sun position vLSR = 238 km s −1 and a Sun’s peculiar velocity vector v = [U,V,W] = [14.0,12.24,7.25] km s −1 (Schönrich et al. 2010 Schönrich 2012 Bland-Hawthorn & Gerhard 2016)." [2]

Def. a star moving faster than 65 km/s to 100 km/s relative to the average motion of the stars in the Sun's neighbourhood is called a high-velocity star.

Def. a high-velocity star moving through space with an abnormally high velocity relative to the surrounding interstellar medium is called a runaway star.

Def. a star whose elliptical orbit takes it well outside the plane of [its galaxy] at steep angles is called a halo star.

1. Gravitational interactions between stars in a stellar system can result in large accelerations of one or more of the involved stars. In some cases, stars may even be ejected. [3] This can occur in seemingly stable star systems of only three stars, as described in studies of the three-body problem in gravitational theory. [4]
2. A collision or close encounter between stellar systems, including galaxies, may result in the disruption of both systems, with some of the stars being accelerated to high velocities, or even ejected. A large-scale example is the gravitational interaction between the Milky Way Galaxy and the Large Magellanic Cloud. [5]
3. A supernova explosion in a multiple star system can accelerate both the supernova remnant and/or remaining stars to high velocities. [6][7]

"Stars with extremely high velocities have been long studied to probe our Galaxy. The interest in the high velocity tail of the total velocity distribution of stars in our Milky Way is twofold. First, it flags the presence of extreme dynamical and astrophysical processes, especially when the velocity of a star is so high that it approaches (or even exceeds) the escape speed from the Galaxy at its position. Secondly, high velocity stars, spanning a large range of distances, can be used as dynamical tracers of integral properties of the Galaxy. The stellar high velocity distribution has for example been used to trace the local Galactic escape speed and the mass of the Milky Way (e.g. Smith et al. 2007 Gnedin et al. 2010 Piffl et al. 2014). To put the concept of high velocity in context, the value of the escape speed is found to be ∼ 530 km s −1 at the Sun position, it increases up to ∼ 600 km s −1 in the central regions of the Galaxy, and then falls down to ≲ 400 km s −1 at Galactocentric distances ∼ 50 kpc (Williams et al. 2017)." [2]

On the right is an image of WR 124 a Wolf–Rayet star in the constellation of Sagitta surrounded by a ring nebula of expelled material known as M1-67. [8]

Its a runaway star with a radial velocity around 200 km/s, discovered in 1938, and identified as a high velocity Wolf–Rayet star. [9] It is listed in the General Catalogue of Variable Stars as QR Sagittae with a range of 0.08 magnitudes. [10]

The Gaia Data Release 2 parallax is 0.1153 ± 0.0365 mas , leading to a statistical distance estimate of 6 , 203 1 , 123 1 , 621 _<1,123>^<1,621>> pc. [11]

The expansion rate of the M1-67 nebula expelled from the star has been directly measured using the Hubble WFPC2 camera images taken 11 years apart, and compared that rate to the expansion velocity measured by the Doppler shift of the nebular emission lines. [12] The distance calculated from the nebular expansion rate is 3.35 kpc. [12] Previous distances of 5kpc [8] to 8.4kpc, [13] have corresponding luminosities of 338,000-1,000,000 L.

WR stars of lower metallicity can form from lower mass progenitors and have lower luminosity, but this would be unusual for a Population I star within the Milky Way. [12] A young highly massive and luminous WN8h star would still be burning hydrogen in its core, but a less luminous and older star would be burning helium in its core. [14] The result of modelling the star purely from its observed characteristics is a luminosity of 1,000,000 L and a mass of 33 M, corresponding to a relatively young hydrogen-burning star at around 8 kpc [13] The mass loss rate is 10 −5 - 10 −4 M per year, depending on the distance and properties determined for the star. [8] WR 124 can be seen as a glowing body in the center of a gigantic fireball. [8]

"A first class of objects that can be found in the high tail of the total velocity distribution is fast halo stars. Their measured dispersion velocity is around 150 km s −1 (Smith et al. 2009 Evans et al. 2016), therefore 3-σ outliers can exceed 450 km s −1 , while remaining bound. Halo stars could also reach unbound velocities, when they are part of the debris of tidally disrupted satellite galaxies, like the Sagittarius Dwarf galaxy, that has not yet virialized (e.g. Abadi et al. 2009). Velocities outliers in the bulge and disk velocity distribution may also exist and become apparent in a large data set." [2]

"Looking towards the constellation of Triangulum (The Triangle), in the northern sky, lies the galaxy pair MRK 1034. The two very similar galaxies, named PGC 9074 and PGC 9071, are close enough to one another to be bound together by gravity, although no gravitational disturbance can yet be seen in the image. These objects are probably only just beginning to interact gravitationally." [15]

"Both are spiral galaxies, and are presented to our eyes face-on, so we are able to appreciate their distinctive shapes. On the left of the image, spiral galaxy PGC 9074 shows a bright bulge and two spiral arms tightly wound around the nucleus, features which have led scientists to classify it as a type Sa galaxy. Close by, PGC 9071 — a type Sb galaxy — although very similar and almost the same size as its neighbour, has a fainter bulge and a slightly different structure to its arms: their coils are further apart." [15]

"The spiral arms of both objects clearly show dark patches of dust obscuring the light of the stars lying behind, mixed with bright blue clusters of hot, recently-formed stars. Older, cooler stars can be found in the glowing, compact yellowish bulge towards the centre of the galaxy. The whole structure of each galaxy is surrounded by a much fainter round halo of old stars, some residing in globular clusters." [15]

"Gradually, these two neighbours will attract each other, the process of star formation will be increased and tidal forces will throw out long tails of stars and gas. Eventually, after maybe hundreds of millions of years, the structures of the interacting galaxies will merge together into a new, larger galaxy." [15]

Variable type: BY Draconis variable (BY Dra) [16] , Temperature = 3550 ± 50 K [17] , Rotational velocity = 9.15 km/s [18] , Visibility: The star is at an apparent magnitude of 9 and is visible through binoculars or a telescope in the constellation of Pictor, in the southern sky. [19]

Radial velocity (cz) = 245.29 ± 0.10 km/s, Spectral type: M1VIp, V* VZ Pic, HD 33793, IRAS 05100-4502, 2MASS J05114046-4501051 and Gaia DR2 4810594479417465600. [20]

""Runaway stars" (RSs) form an another class of high velocity stars. They were originally introduced as O and B type stars ejected from the Galactic disk with velocities higher than 40 km s −1 (Blaauw 1961). Theoretically, there are two main formation channels: i) dynamical encounters between stars in dense stellar systems such as young star clusters (e.g. Poveda et al. 1967 Leonard & Duncan 1990 Gvaramadze et al. 2009), and ii) supernova explosions in stellar binary systems (e.g. Blaauw 1961 Portegies Zwart 2000). Both mechanisms have been shown to occur in our Galaxy (Hoogerwerf et al. 2001). Typical velocities attained by the two formation channels are of the order of a few tens of km s −1 , and even if several hundreds of km s −1 can be attained for the most extreme systems (Portegies Zwart 2000 Przybilla et al. 2008 Gvaramadze et al. 2009 Gvaramadze & Gualandris 2011 Silva & Napiwotzki 2011), simulations indicate that the majority of runaway stars from dynamical encounters have ejection velocities ≲ 200 km s −1 (Perets & Šubr 2012). Recent results show that it is possible to achieve ejection velocities up to ∼ 1300 km s −1 for low-mass G/K type stars in very compact binaries (Tauris 2015). Nevertheless, the rate of production of unbound RSs, referred to as hyper runaway stars (HRSs), is estimated to be as low as 8 · 10 −7 yr −1 (Perets & Šubr 2012 Brown 2015)." [2]

"A heavy runaway star rushing away from a nearby stellar nursery at more than 400 000 kilometres per hour, a speed that would get you to the Moon and back in two hours [is shown in the image on the right]. The runaway is the most extreme case of a very massive star that has been kicked out of its home by a group of even heftier siblings. Tantalising clues from three observatories, including the NASA/ESA Hubble Space Telescope’s newly installed Cosmic Origins Spectrograph (COS), and some old-fashioned detective work, suggest that the star may have travelled about 375 light-years from its suspected home, a giant star cluster called R136." [21]

"The homeless star is on the outskirts of the 30 Doradus Nebula, a raucous stellar breeding ground in the nearby Large Magellanic Cloud. The finding bolsters evidence that the most massive stars in the local Universe reside in 30 Doradus, making it a unique laboratory for studying heavyweight stars. 30 Doradus, also called the Tarantula Nebula, is roughly 170 000 light-years from Earth. Nestled in the core of 30 Doradus, R136 contains several stars topping 100 solar masses each." [21]

"The observations offer insights into how massive star clusters behave." [21]

"These results are of great interest because such dynamical processes in very dense, massive clusters have been predicted theoretically for some time, but this is the first direct observation of the process in such a region. Less massive runaway stars from the much smaller Orion Nebula Cluster were first found over half a century ago, but this is the first potential confirmation of more recent predictions applying to the most massive young clusters." [22]

"Runaway stars can be made in a couple of ways. A star may encounter one or two heavier siblings in a massive, dense cluster and get booted out through a stellar game of pinball. Or, a star may get a “kick” from a supernova explosion in a binary system, with the more massive star exploding first." [21]

"It is generally accepted, however, that R136 is young enough that the cluster’s most massive stars have not yet exploded as supernovae. This implies that the star must have been ejected through dynamical interaction." [23]

"Hubble astronomers unexpectedly picked up another clue when they used the star as a target to calibrate the COS instrument, installed in May 2009 during Servicing Mission 4. Those ultraviolet spectroscopic observations, made in July 2009, showed that the wayward star is unleashing a fury of charged particles in one of the most powerful stellar winds known, a clear sign that it is extremely massive, perhaps as much as 90 times heavier than the Sun. The star, therefore, also must be very young, about one million to two million years old, because extremely massive stars only live for a few million years." [21]

"Sifting through Hubble’s archive of images, astronomers found another important piece of evidence. An optical image of the star taken by the Wide Field Planetary Camera 2 in 1995 revealed that it is at one end of an egg-shaped cavity. The cavity’s glowing edges stretch behind the star and point in the direction of its home in 30 Doradus." [21]

"Another spectroscopic study from the European Southern Observatory’s Very Large Telescope (VLT) at the Paranal Observatory in Chile revealed that the star’s velocity is constant and not a result of orbital motion in a binary system. Its velocity corresponds to an unusual motion relative to the star’s surroundings, evidence that it is a runaway star." [21]

"The study also confirmed that the light from the runaway is from a single massive star rather than the combined light of two lower mass stars. In addition, the observation established that the star is about ten times hotter than the Sun, a temperature that is consistent with a high-mass object." [21]

Spectral type: O9.5V [24] , Variable type: Orion variable [25] , Radial velocity = 56.70 ± 0.6 km/s [26] , Temperature: 33,000 K [27] , and Rotational velocity = 25 km/s. [27]

AE Aur is a runaway star that might have been ejected during a collision of two binary star groups, which also is credited with ejecting Mu Columbae and possibly 53 Arietis, and has been traced to the Trapezium cluster in the Orion Nebula two million years ago, where the binary Iota Orionis may have been the other half of this collision. [28]

AE Aur is seen to light up the Flaming Star nebula, but it was not formed within it and is passing through the nebula at high speed producing a violent bow shock and high energy electromagnetic radiation. [29] [30]

Spectral class: O9 III + B0.8 III/IV [31] , Variable type: (B) Orion [32] , Radial velocity (cz) = 21.5 km/s [33] , Temperature (ι Ori Aa) = 32,500 K [31] , Rotational velocity = 122 km/s [34] , Temperature (ι Ori Ab) = 27,000 K [31] , Temperature (ι Ori B) = 18,000 K [35]

Iota Orionis (ι Orionis, abbreviated ι Ori) is a multiple star system in the equatorial constellation of Orion the hunter, the eighth-brightest member of Orion with an apparent visual magnitude of 2.77, the brightest member of the asterism known as Orion's Sword, a member of the NGC 1980 open cluster, and from parallax measurements, is located at a distance of roughly 2,300 light-years (710 parsecs) from the Sun. [36]

The system has three components designated Iota Orionis A, B and C, where Iota Orionis A is itself a massive spectroscopic binary, with components Iota Orionis Aa (officially named Hatysa [37] and Ab, plus B and C. [38]

Iota Orionis is dominated by Iota Orionis A whose two components are a stellar class O9 III star (blue giant) and a class B0.8 III/IV star about 2 magnitudes fainter. [31] The collision of the stellar winds from this pair makes the system a strong X-ray source, but the two objects of this system appear to have different ages, with the secondary being about double the age of the primary, where in combination with the high eccentricity (e=0.764) of their 29-day orbit, the binary system may have been created through a capture, rather than by being formed together and undergoing a mass transfer, for example, through an encounter between two binary systems. [31] [39]

Iota Orionis B is a B8 giant at 11" (approximately 5,000 AU [35] ) which has been shown to be variable, and likely to be a young stellar object. [40] The fainter Iota Orionis C is an A0 star at 49". [41]

NGC 1980 contains few bright stars other than Iota Orionis, where only eighteen other stars are considered members in a survey down to 14th magnitude, most around 9th magnitude but including the 5th magnitude stars HR 1886 and 1887. [42]

"As a class, the fastest stars in our Galaxy are expected to be hypervelocity stars (HVSs). These were first theoretically predicted by Hills (1988) as the result of a three-body interaction between a binary star and the massive black hole in the Galactic Centre (GC), Sagittarius A * . Following this close encounter, a star can be ejected with a velocity ∼ 1000 km s −1 , sufficiently high to escape from the gravitational field of the Milky Way (Kenyon et al. 2008 Brown 2015). The first HVS candidate was discovered by Brown et al. (2005): a B-type star with a velocity more than twice the Galactic escape speed at its position. Currently about ∼ 20 unbound HVSs with velocities ∼ 300 - 700 km s −1 have been discovered by targeting young stars in the outer halo of the Milky Way (Brown et al. 2014)." [2]

"HVSs are predicted to be ejected from the GC with an uncertain rate around 10 −4 yr −1 (Yu & Tremaine 2003 Zhang et al. 2013), two orders of magnitude larger than the rate of ejection of runaway stars with comparable velocities from the stellar disk (Brown 2015). Because of their extremely high velocities, HVS trajectories span a large range of distances, from the GC to the outer halo." [2]

Stars considered hypervelocity stars are those with radial velocity greater than |299| km/s, or 299 km/s < v < -299 km/s.

Stars "sharing the same formation scenario as HVSs, but with an ejection velocity which is not sufficiently high to escape from the whole Milky Way (e.g. Bromley et al. 2006). Most of the deceleration occurs in the inner few kpc due to the bulge potential (Kenyon et al. 2008), and the minimum velocity necessary at ejection to be unbound is of the order of ∼ 800 km s −1 (a precise value depends on the choice of the Galactic potential, Brown 2015 Rossi et al. 2017). If we consider the Hills mechanism , this population of bound stars is expected to be dominant over the sample of HVSs (Rossi et al. 2014 Marchetti et al. 2018)." [2]

"At the moment, the fastest star discovered in our Galaxy is US 708, traveling away from the Milky Way with a total velocity ∼ 1200 km s −1 (Hirsch et al. 2005). Its orbit is not consistent with coming from the GC (Brown et al. 2015), and the most likely mechanism responsible for its acceleration is the explosion of a thermonuclear supernova in an ultra-compact binary in the Galactic disk (Geier et al. 2015)." [2]

km/s, ROSAT X-ray source 1RXS J011758.8+651730, Ariel X-ray source 3A 0114+650, SWIFT J0117.8+6516 X-ray source, and INTEGRAL1 1 gamma-ray source. [43]

4U 1700-37 is one of the stronger binary X-ray sources in the sky, and is classified as a high-mass X-ray binary that was discovered by the Uhuru satellite. [44]

Radial velocity = −75.00 ± 7.4 km/s. [45]

Variable type is Ellipsoidal]] + High-mass X-ray binaries (HMXB) [25]

Optical component is HD 153919, Radial velocity (cz) = 33.38 ± 6.93 km/s, INTEGRAL1 39 (gamma-ray source), Einstein catalog 2E 1700.5-3746 (X-ray source), TD1 19850 (ultraviolet source). [47]

The image on the left shows a high velocity binary star and the comet-like trail behind it is light years long. The binary is plowing through the interstellar medium. It's radiating, been radiated, and packs a punch!

"Ultra-violet studies of Mira by NASA's Galaxy Evolution Explorer (Galex) space telescope have revealed that it sheds a trail of material from the outer envelope, leaving a tail 13 light-years in length, formed over tens of thousands of years. [48] [49] It is thought that a hot bow-wave of compressed plasma/gas is the cause of the tail the bow-wave is a result of the interaction of the stellar wind from Mira A with gas in interstellar space, through which Mira is moving at an extremely high speed of 130 kilometres/second (291,000 miles per hour). [50] [51] The tail consists of material stripped from the head of the bow-wave, which is also visible in ultra-violet observations. Mira's bow-shock will eventually evolve into a planetary nebula, the form of which will be considerably affected by the motion through the interstellar medium (ISM). [52]

At second right is the only available X-ray image, by the Chandra X-ray Observatory, of Mira A on the right and Mira B (left). "Mira A is losing gas rapidly from its upper atmosphere [apparently] via a stellar wind. [Mira B is asserted to be a white dwarf. In theory] Mira B exerts a gravitational tug that creates a gaseous bridge between the two stars. Gas from the wind and bridge accumulates in an accretion disk around Mira B and collisions between rapidly moving particles in the disk produce X-rays." [53]

Mira A, spectral type M7 IIIe [54] , has an effective surface temperature of 2918–3192 [55] . Mira A is not a known X-ray source according to SIMBAD, but here is shown to be one.

Mira A, spectral type M7 IIIe [54] , has an effective surface temperature of 2918–3192 [55]

At right "is a NASA Hubble Space Telescope image of the cool red giant star Mira A (right), officially called Omicron Ceti in the constellation Cetus, and its nearby hot companion (left) taken on December 11, 1995 in visible light using the European Space Agency's Faint Object Camera (FOC). The stars in this false-color picture are separated by an angular size of only 0.6 arcseconds (equal to 70 times the distance between Earth and the Sun), but clearly resolved by the FOC. Image reconstruction techniques have been used to further enhance the details in the Mira images." [56]

Mira B, also known as VZ Ceti, is the companion star to the variable star Mira. Its orbit around Mira is poorly known the most recent estimate listed in the Sixth Orbit Catalog of Visual Binary Stars gives an orbital period of roughly 500 years, with a periastron around the year 2285. Assuming the distance in the Hipparcos catalog and orbit are correct, Mira A and B are separated by an average of 100 AU.

Long-known to be erratically variable itself, its fluctuations seem to be related to its accretion of matter from Mira's stellar wind, which makes it a symbiotic star. [57] [58]

The new data suggest that Mira B is a normal main sequence star of spectral type K and roughly 0.7 solar masses, rather than a white dwarf as first envisioned. [59]

Even more recently (2010) analysis of rapid optical brightness variations has indicated that Mira B is in fact a white dwarf. [60]

Radial velocity (cz) = 338.45 ± 2.62 km/s, Spectral type: F2V, aka Gaia DR1 5489531875795980032, Gaia DR2 5489531880096156416, and 2MASS J07532122-5239133. [61]

Radial velocity (cz) = 333.17 ± 0.35 km/s, Spectral type: G5V, 2MASS J07393021-5548171 is aka Gaia DR1 5487974692453649792, Gaia DR2 5487974692453649792 and OM 96. [62]

"The extragalactic star with a highest probability of being unbound from our Galaxy is Gaia DR2 1396963577886583296, with a total velocity ∼ 700 km s −1 , resulting in a probability Pub = 0.98. [. ] This star is at ∼ 30 kpc from the GC, with an elevation of ∼ 25 kpc above the Galactic plane." [2]

Radial velocity (cz) = 378.65 ± 1.11 km/s. [63]

Radial velocity (cz) = -318.40 ± 0.59 km/s [64]

Radial velocity (cz) = 319.79 ± 0.67 km/s, 2MASS J01095931-6808494 is aka OM 1, RAVE J010959.3-680849, UCAC2 2064411, UCAC3 44-2237, and UCAC4 110-001006. [65]

Radial velocity (cz) = 300.36 ± 5.02 km/s, Spectral type: A5III, ASAS J060746-6658.6 is aka CSV 725, GCRV 26604, GSC 08905-00975, HIP 29055, 2MASS J06074571-6658388, Gaia DR1 5283957629860435072, Gaia DR2 5283957629860435072, OM 89, RAVE J060745.7-665839, SSTISAGEMC J060745.70-665838.9, SV* BV 458, SV* HV 7641, SV* HV 12250, TYC 8905-975-1, UCAC4 110-001006, and uvby98 620198089. [66]

HD 271791 is a B-type hyperrunaway star ejected from the Galactic disk. [67]

"HD 271791 (Heber et al. 2008) [is] a 11 ± 1 M B-giant stars established to be a run-away star with velocity similar to those of hypervelocity stars. HD 271791 is 21.8 ± 3.7 kpc away from the GC and −10.4 ± 2.0 kpc below the disk plane (Heber et al. 2008)". [68]

Radial velocity (cz) = 366.22 ±

km/s, Spectral type: B2(III), 2MASS J06022786-6647286 is aka Gaia DR2 5284151216932205312, GCRV 26603, HIP 28618, OM 88, SSTISAGEMC J060227.86-664728.7, TYC 8905-1908-1, and uvby98 620198088. [69]

"A hundred million years ago, a triple-star system was traveling through the bustling center of our Milky Way galaxy when it made a life-changing misstep. The trio wandered too close to the galaxy's giant black hole, which captured one of the stars and hurled the other two out of the Milky Way. Adding to the stellar game of musical chairs, the two outbound stars merged to form a super-hot, blue star." [70]

"This story may seem like science fiction, but astronomers using NASA's Hubble Space Telescope say it is the most likely scenario for a so-called hypervelocity star, known as HE 0437-5439, one of the fastest ever detected. It is blazing across space at a speed of 1.6 million miles (2.5 million kilometers) an hour, three times faster than our Sun's orbital velocity in the Milky Way. Hubble observations confirm that the stellar speedster hails from the Milky Way's core, settling some confusion over where it originally called home." [70]

"Most of the roughly 16 known hypervelocity stars, all discovered since 2005, are thought to be exiles from the heart of our galaxy. But this Hubble result is the first direct observation linking a high-flying star to a galactic center origin." [70]

"Using Hubble, we can for the first time trace back to where the star comes from by measuring the star's direction of motion on the sky. Its motion points directly from the Milky Way center. These exiled stars are rare in the Milky Way's population of 100 billion stars. For every 100 million stars in the galaxy lurks one hypervelocity star." [71]

"Studying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form. Dark matter's gravitational pull is measured by the shape of the hyperfast stars' trajectories out of the Milky Way." [70]

"The stellar outcast is already cruising in the Milky Way's distant outskirts, high above the galaxy's disk, about 200,000 light-years from the center. By comparison, the diameter of the Milky Way's disk is approximately 100,000 light-years. Using Hubble to measure the runaway star's direction of motion and determine the Milky Way's core as its starting point, [the] team calculated how fast the star had to have been ejected to reach its current location." [70]

"The star is traveling at an absurd velocity, twice as much as the star needs to escape the galaxy's gravitational field. There is no star that travels that quickly under normal circumstances – something exotic has to happen." [71]

"There's another twist to this story. Based on the speed and position of HE 0437-5439, the star would have to be 100 million years old to have journeyed from the Milky Way's core. Yet its mass – nine times that of our Sun – and blue color mean that it should have burned out after only 20 million years – far shorter than the transit time it took to get to its current location." [70]

"The most likely explanation for the star's blue color and extreme speed is that it was part of a triple-star system that was involved in a gravitational billiard-ball game with the galaxy's monster black hole. This concept for imparting an escape velocity on stars was first proposed in 1988. The theory predicted that the Milky Way's black hole should eject a star about once every 100,000 years." [70]

"The triple-star system contained a pair of closely orbiting stars and a third outer member also gravitationally tied to the group. The black hole pulled the outer star away from the tight binary system. The doomed star's momentum was transferred to the stellar twosome, boosting the duo to escape velocity from the galaxy. As the pair rocketed away, they went on with normal stellar evolution. The more massive companion evolved more quickly, puffing up to become a red giant. It enveloped its partner, and the two stars spiraled together, merging into one superstar – a blue straggler." [71]

"While the blue straggler story may seem odd, you do see them in the Milky Way, and most stars are in multiple systems." [71]

"This vagabond star has puzzled astronomers since its discovery in 2005 by the Hamburg/European Southern Observatory sky survey. Astronomers had proposed two possibilities to solve the age problem. The star either dipped into the Fountain of Youth by becoming a blue straggler, or it was flung out of the Large Magellanic Cloud, a neighboring galaxy." [70]

"In 2008 a team of astronomers thought they had solved the mystery. They found a match between the exiled star's chemical makeup and the characteristics of stars in the Large Magellanic Cloud. The rogue star's position also is close to the neighboring galaxy, only 65,000 light-years away. The new Hubble result settles the debate over the star's birthplace." [70]

"Astronomers used the sharp vision of Hubble's Advanced Camera for Surveys to make two separate observations of the wayward star 3 1/2 years apart. Team member Jay Anderson of the Space Telescope Science Institute in Baltimore, Md., developed a technique to measure the star's position relative to each of 11 distant background galaxies, which form a reference frame." [70]

"Anderson then compared the star's position in images taken in 2006 with those taken in 2009 to calculate how far the star moved against the background galaxies. The star appeared to move, but only by 0.04 of a pixel (picture element) against the sky background." [70]

"Hubble excels with this type of measurement. This observation would be challenging to do from the ground." [72]

"The team is trying to determine the homes of four other unbound stars, all located on the fringes of the Milky Way." [70]

"We are targeting massive 'B' stars, like HE 0437-5439. These stars shouldn't live long enough to reach the distant outskirts of the Milky Way, so we shouldn't expect to find them there. The density of stars in the outer region is much less than in the core, so we have a better chance to find these unusual objects." [71]

"HE 0437-5439 is a B-type star, and is likely to be originated from the centre of the Large Magellanic Cloud (LMC) (Erkal et al. 2018)." [67]

"HE 0437-5439 (a.k.a HVS 3 e.g., Edelmann et al. 2005 Bonanos et al. 2008 Przybilla et al. 2008), which is also a ∼9 M B-type star". [68]

Radial velocity (cz) = 723.87 ±

km/s, Spectral type: sdB+F, [BGK2006] HV 3 is aka Gaia DR2 4777328613382967040. [73]

## More hypervelocity stars are jetting out of the galaxy

Title: Hypervelocity Star Candidates in the Segue G & K Dwarf Sample
Authors: Lauren E. Palladino, Katharine J. Schlesinger, Kelley Holley-Bockelmann, Carlos Allende Prieto, Timothy C. Beers, Young Sun Lee, & Donald P. Schneider
First Author’s Institution: Vanderbilt University, Nashville, Tennessee

In 1988, J. G. Hills predicted that binary stars near the center of our galaxy would occasionally interact with Sgr A*, the galaxy’s supermassive black hole, causing one star to be ejected from the system with enough energy to completely escape the galaxy’s gravitational pull. In the 2000’s several so-called “hypervelocity stars” (HVSs) were detected, and indeed these objects were giant stars with orbits consistent with ejections from the galactic center. More recently, other theories have been proposed to create HVSs, including anisotropies in the galactic potential and energetic “kicks” induced by nearby supernovae. The authors of this paper present a new collection of potential hypervelocity stars that appear not to originate in the galactic center, and discuss their potential origins with respect to these theories.

At the end of the Sloan Digital Sky Survey (SDSS) mission, the SDSS telescope was used to create the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey (discussed in this Astrobite), which obtained spectroscopic information on nearly 250,000 stars in the galaxy. The authors analyzed 70,000 G (solar type) and K (slightly sub-solar) dwarfs in this survey, measuring their Doppler shift and proper motion. The Doppler shift corresponds exactly to the radial velocity of a star, independent of the distance to the star. Proper motion, however, is related to both the tangential velocity and the distance to a star. If a star has a large angular proper motion, it could either be moving rapidly, or simply be nearby. The product of the star’s proper motion and its distance is directly proportional to its tangential velocity. To estimate the distance to each star, the authors estimate its spectral type (and thus true luminosity) from the observed spectrum, and compare that to the observed flux. This method requires an estimate of the amount of absorption by dust in the interstellar medium along the light’s path from the star to our telescope if this value is incorrectly estimated the distance to the star can be significantly mismeasured.

Metallicity distribution for the HVS candidates (gray) compared to the metallicities of disk stars (top), globular clusters (middle), and bulge stars (bottom). This sample appears to be most consistent with stars in the galactic disk.

The authors measure each star’s tangential and radial velocity and select for their sample those stars having a total velocity vector larger than 600 kilometers/second, fast enough to escape the galaxy. This sample contains 13 targets. It is worth noting that in many of these cases, the (more robustly measured) radial velocities are quite small, while the tangential velocities are very large. If these stars have had their distances significantly overestimated, then their tangential velocities are correspondingly smaller and the stars may not actually be HVSs. Moreover, the proper motions are small (around 0.05 arcseconds per year for these stars), and the measurement uncertainties are large (around 0.01 arcseconds per year), so out of a sample of 70,000 stars, a few systems would be expected to have significantly overestimated proper motions simply by chance alone. For each star the authors provide a probability that the star is an “interloper” with a much smaller true proper motion these values range from 0.004 to 0.6 (0.4 to 60 %). The authors note that this sample is simply a list of candidates, and more follow-up is needed to separate the true HVSs from false positive interlopers.

Orbits of the 13 HVS candidates integrated backward in time for 1 billion years. The black dot corresponds to the location of the supermassive black hole none of the stars appear to originate from this area of the galaxy. Moreover, most of these orbits are tilted out of the plane of the galaxy (not shown here).

Now that we have a sample of potential hypervelocity stars, where do they come from? The authors first look at the metallicity distribution of the stars and compare it to samples of other stars in the galaxy (above right). They find the HVS G and K dwarf candidates are similar to the distribution of G and K stars in the galactic disk. They find Milky Way bulge stars are much more metal rich than this sample, while stars in globular clusters are much more metal poor. This suggests that these stars originate in the disk, not the bulge near the galactic center or the galactic halo. The authors then use the positions and velocities of each star and integrate their orbits backward in time to determine their origins (at left). They find the stars do not all originate from the same section of the galaxy and none come from the galactic center. Therefore, while the origins of the stars are unclear, their metallicity distribution and velocities are consistent with these objects not originating from near the central black hole.

More followup work will be needed to study the origin of these stars and determine which are true HVSs (by improving our estimate of the distances to the stars and their proper motions) to better understand their origins and history, but for now it seems like the galactic center hypothesis is incomplete.

## Hypervelocity Star Surpasses Escape Velocity of the Milky Way Galaxy

A hundred million years ago, a triple-star system was traveling through the bustling center of our Milky Way galaxy when it made a wrong turn. The trio wandered too close to the galaxy's giant black hole, which ate one of the stars and hurled the other two out of the Milky Way. Adding to the stellar game of musical chairs, the two outbound stars merged to form a super-hot blue star.

This story may seem like a fairy tale, but astronomers using NASA's Hubble Space Telescope say it is the most likely scenario for a so-called hypervelocity star, known as HE 0437-5439, one of the fastest ever detected. It's blazing across space at a speed of 1.6 million miles (2.5 million kilometers) an hour, three times faster than our Sun's orbital velocity in the Milky Way. Hubble observations confirm that the stellar speedster hails from the Milky Way's core, settling some confusion over where it originally called home.

Most of the roughly 16 known hypervelocity stars, all discovered since 2005, are thought to be exiles from the heart of our galaxy. But this Hubble result is the first direct observation linking a high-flying star to a galactic center origin.

"Using Hubble, we can for the first time trace back to where the star comes from by measuring the star's direction of motion on the sky. Its motion points directly from the Milky Way center," says astronomer Warren Brown of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., a member of the Hubble team that observed the star. "These exiled stars are rare in the Milky Way's population of 100 billion stars. For every 100 million stars in the galaxy lurks one hypervelocity star."

The movements of these unbound stars could reveal the shape of the dark matter distribution surrounding our galaxy. "Studying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form," says team leader Oleg Gnedin of the University of Michigan in Ann Arbor. "Dark matter's gravitational pull is measured by the shape of the hyperfast stars' trajectories out of the Milky Way."

The stellar outcast is already cruising in the Milky Way's distant outskirts, high above the galaxy's disk, about 200,000 light-years from the center. By comparison, the diameter of the Milky Way's disk is approximately 100,000 light-years. Using Hubble to measure the runaway star's direction of motion and determine the Milky Way's core as its starting point, Brown and Gnedin's team calculated how fast the star had to have been ejected to reach its current location.

"The star is traveling at an absurd velocity, twice as much as the star needs to escape the galaxy's gravitational field," explains Brown, a hypervelocity star hunter who found the first unbound star in 2005. "There is no star that travels that quickly under normal circumstances - something exotic has to happen."

There's another twist to this story. Based on the speed and position of HE 0437-5439, the star would have to be 100 million years old to have journeyed from the Milky Way's core. Yet its mass - nine times that of our Sun - and blue color mean that it should have burned out after only 20 million years - far shorter than the transit time it took to get to its current location.

The most likely explanation for the star's blue color and extreme speed is that it was part of a triple-star system that was involved in a gravitational billiard-ball game with the galaxy's monster black hole. This concept for imparting an escape velocity on stars was first proposed in 1988. The theory predicted that the Milky Way's black hole should eject a star about once every 100,000 years.

Brown suggests that the triple-star system contained a pair of closely orbiting stars and a third outer member also gravitationally tied to the group. The black hole pulled the outer star away from the tight binary system. The doomed star's momentum was transferred to the stellar twosome, boosting the duo to escape velocity from the galaxy. As the pair rocketed away, they went on with normal stellar evolution. The more massive companion evolved more quickly, puffing up to become a red giant. It enveloped its partner, and the two stars spiraled together, merging into one superstar - a blue straggler.

"While the blue straggler story may seem odd, you do see them in the Milky Way, and most stars are in multiple systems," Brown says.

This vagabond star has puzzled astronomers since its discovery in 2005 by the Hamburg/European Southern Observatory sky survey. Astronomers had proposed two possibilities to solve the age problem. The star either dipped into the Fountain of Youth by becoming a blue straggler, or it was flung out of the Large Magellanic Cloud, a neighboring galaxy.

In 2008 a team of astronomers thought they had solved the mystery. They found a match between the exiled star's chemical makeup and the characteristics of stars in the Large Magellanic Cloud. The rogue star's position also is close to the neighboring galaxy, only 65,000 light-years away. The new Hubble result settles the debate over the star's birthplace.

Astronomers used the sharp vision of Hubble's Advanced Camera for Surveys to make two separate observations of the wayward star 3 1/2 years apart. Team member Jay Anderson of the Space Telescope Science Institute in Baltimore, Md., developed a technique to measure the star's position relative to each of 11 distant background galaxies, which form a reference frame. The team is trying to determine the homes of four other unbound stars, all located on the fringes of the Milky Way.

"We are targeting massive 'B' stars, like HE 0437-5439," says Brown, who has discovered 14 of the 16 known hypervelocity stars. "These stars shouldn't live long enough to reach the distant outskirts of the Milky Way, so we shouldn't expect to find them there. The density of stars in the outer region is much less than in the core, so we have a better chance to find these unusual objects."

## Could We Travel To Another Galaxy Using Hypervelocity Stars?

The thought of traveling to a distant star is daunting enough, let alone the prospect of facing millions of years of flight time to reach the nearest galaxy. Remarkably, the discovery of galaxy-escaping hypervelocity stars may provide a solution.

In a recent paper, discussed here by Adam Crowl, Robin Spivey ponders "autonomous probes that spawn life upon arrival" as a way of reaching the Virgo cluster, which he wants to do for reasons Adam explained in his post. He's also counting on continuous acceleration at 1 g for these small 'seed ships,' but other than mentioning antimatter, he doesn't explore how this would be done, and we've seen the results Sagan and Iosif S. Shklovskii came up with for antimatter when they worked out the equations.

Let's assume that the 'slow boat' solution is the only practical way to proceed. Here I think Adam's suggestion that we take our environment with us rather than building a worldship is sensible, flinging a small star and planet out of the galactic core toward the destination. Ray Villard pondered the same question back in 2010 in an online piece called " The Great Escape: Intergalactic Travel is Possible ." He points to the four million solar mass black hole at the center of the Milky Way as the only conceivable way to impart the needed kinetic energy to a star.

Here's how Villard describes the mechanism:

The theory is that a star could be slingshot out of a binary star system if the stellar duo swung close to the central black hole. The hole's gravitational tidal forces would break apart the pair's gravitational embrace.

The companion star orbiting in the direction of the black hole would pick up momentum and plunge toward the black hole. In accordance with Newton's third law of motion — action-reaction — the other binary companion would go whizzing off with the same velocity but opposite direction away from the black hole.

In just a few thousand years the star would ascend out of the galactic plane and hurtle deep into intergalactic space. The persistent tug of our Milky Way's dark matter halo would slow it down but the star would never fall back into the Galaxy.

Using ESO's Very Large Telescope, astronomers have recorded a massive star moving at more than 2.6 million kilometres per hour (1160 km/sec). Credit: ESO.

We do in fact know about a number of such hypervelocity stars, some of which may be moving fast enough to exceed galactic escape velocity . Consider this: Ordinary stars in the Milky Way have velocities in the range of 100 kilometers per second, while some hypervelocity stars near galactic center show velocities of ten times that, closing on 1,000 km/sec. Meanwhile, a team led by Tilmann Piffl (Leibniz Institute for Astrophysics, Potsdam) that has been working with high-velocity stars has calculated escape velocity for objects in the vicinity of our own Solar System. The team uses data from the Radial Velocity Experiment (RAVE) survey.

###### An entirely new class of galaxy-escaping hypervelocity stars

Every once in a while, the Milky Way's supermassive black hole flings a wayward star into…

The result: We would need 537 kilometers per second to get our payload fast enough to escape the galaxy. That's a high speed, of course, but in terms of small craft, it's not a lot higher than some studies have shown a solar sail could reach using an extremely tight 'Sundiver' maneuver to let itself be whipped out of the Solar System. Piffl's team has catalogued hypervelocity stars moving at 300 km/sec, and we also know of unbound hypervelocity stars (although it's a tricky call because of uncertainties about the mass distribution of the galaxy). Even some neutron stars are fast-movers: RX J0822-4300 was measured to move at 1500 km/sec in 2007.

Not all hypervelocity stars come from encounters with the black hole at galactic center. In work described at the American Astronomical Society meeting in January, Kelly Holley-Bockelmann and grad student Lauren Palladino found what may be a new class of hypervelocity stars moving with sufficient speed to escape the galaxy (see Stars at Galactic Escape Velocity ). Says Holley-Bockelmann:

"It's very hard to kick a star out of the galaxy. The most commonly accepted mechanism for doing so involves interacting with the supermassive black hole at the galactic core. That means when you trace the star back to its birthplace, it comes from the center of our galaxy. None of these hypervelocity stars come from the center, which implies that there is an unexpected new class of hypervelocity star, one with a different ejection mechanism."

As we learn more about what creates hypervelocity stars, can we imagine far future technologies that might help us exploit them? If so, an intergalactic journey opens up. A civilization that somehow harnessed a hypervelocity star for such a journey — or one that arose on a planetary system that had been already flung into intergalactic space — would experience eons in the space between the galaxies, periods that dwarf the lifetime of human civilizations. Villard speculates about the astronomers of such a civilization trying to discover their place in the universe as their 'worldship' exited the Milky Way, globular clusters peppering the sky, the galaxy's spiral arms winding out from a nucleus looking like ɺ fuzzy headlamp.'

Inevitably larger telescopes would yield a view of the universe that revealed myriad other pinwheel structures. Spectroscopy would show they are racing away too. Still the aliens literally wouldn't know if they're coming or going. A long-lived civilization's science archive would note the shrinking and dimming of the Milky Way over geologic time. They might conclude that the eerie pinwheel is speeding away from them. And without a cosmological or stellar framework, they would have no idea of cosmic evolution. They would not even be able to calibrate the vast distance to the Galaxy.

But let's assume for the sake of argument that a civilization might knowingly set out on a hypervelocity star system, its futuristic powers vast enough to shape the encounter between the star and the galactic black hole so as to direct its journey to the proper destination. Any culture that did this would knowingly be splitting into different evolutionary lines given the immensity of the distances and time involved, leaving behind its own species to grow into another over the course of millions of years. Whether and why any species might choose to make this kind of a journey is an exercise left to the reader, and to the imagination of science fiction writers.

We've seen stars manipulated for a variety of purposes in science fiction, as a matter of fact. Tomorrow I'll wrap up this week of speculations on intergalactic travel with a look at some of the methods that have been employed to move stars around, and the possible SETI implications that arise from all this.

The Piffl paper is "The RAVE survey: the Galactic escape speed and the mass of the Milky Way," submitted to Astronomy & Astrophysics ( preprint ). The Palladino paper is "Hypervelocity Star Candidates in the SEGUE G and K Dwarf Sample," The Astrophysical Journal Vol. 780, No. 1 (2014), with abstract and preprint available.

This article originally appeared at Centauri Dreams and is republished here with permission.

## ‘Lopsided’ Supernova Could Be Responsible for Rogue Hypervelocity Stars

Hypervelocity stars have been observed traversing the Galaxy at extreme velocities (700 km/s), but the mechanisms that give rise to such phenomena are still debated. Astronomer Thomas M. Tauris argues that lopsided supernova explosions can eject lower-mass Solar stars from the Galaxy at speeds up to 1280 km/s. “[This mechanism] can account for the majority (if not all) of the detected G/K-dwarf hypervelocity candidates,” he said.

Several mechanisms have been proposed as the source for hypervelocity stars, and the hypotheses can vary as a function of stellar type. A simplified summary of the hypothesis Tauris favors begins with a higher-mass star in a tight binary system, which finally undergoes a core-collapse supernova explosion. The close proximity of the stars in the system partly ensures that the orbital velocities are exceedingly large. The binary system is disrupted by the supernova explosion, which is lopsided (asymmetric) and imparts a significant kick to the emerging neutron star. The remnants of supernovae with massive progenitors are neutron stars or potentially a more exotic object (i.e., black hole).

Conversely, Tauris noted that the aforementioned binary origin cannot easily explain the observed velocities of all higher-mass hypervelocity stars, namely the B-stars, which are often linked to an ejection mechanism from a binary interaction with the supermassive black hole at the Milky Way’s center. Others have proposed that interactions between multiple stars near the centers of star clusters can give rise to certain hypervelocity candidates.

There are several potential compact objects (neutron stars) which feature extreme velocities, such as B2011+38, B2224+65, IGR J11014-6103, and B1508+55, with the latter possibly exhibiting a velocity of 1100 km/s. However, Tauris ends by noting that, “a firm identification of a hypervelocity star being ejected from a binary via a supernova is still missing, although a candidate exists (HD 271791) that’s being debated.”

Tauris is affiliated with the Argelander-Institut für Astronomie and Max-Planck-Institut für Radioastronomie. His findings will be published in the forthcoming March issue of the Monthly Notices of the Royal Astronomical Society.

The interested reader can find a preprint of Tauris’ study on arXiv. Surveys of hypervelocity stars were published by Brown et al. 2014 and Palladino et al. 2014.

## How do Hypervelocity Stars End up Breaking The Speed Limit?

The Sun is racing through the Galaxy at a speed that is 30 times greater than a space shuttle in orbit (clocking in at 220 km/s with respect to the galactic center). Most stars within the Milky Way travel at a relatively similar speed. But certain stars are definitely breaking the stellar speed limit. About one in a billion stars travel at a speed roughly 3 times greater than our Sun – so fast that they can easily escape the galaxy entirely!

We have discovered dozens of these so-called hypervelocity stars. But how exactly do these stars reach such high speeds? Astronomers from the University of Leicester may have found the answer.

The first clue comes in observing hypervelocity stars, where we can note their speed and direction. From these two measurements, we can trace these stars backward in order to find their origin. Results show that most hypervelocity stars begin moving quickly in the Galactic Center.

We now have a rough idea of where these stars gain their speed, but not how they reach such high velocities. Astronomers think two processes are likely to kick stars to such great speeds. The first process involves an interaction with the supermassive black hole (Sgr A*) at the center of our Galaxy. When a binary star system wanders too close to Sgr A*, one star is likely to be captured, while the other star is likely to be flung away from the black hole at an alarming rate.

The second process involves a supernova explosion in a binary system. Dr. Kastytis Zubovas, lead author on the paper summarized here, told Universe Today, “Supernova explosions in binary systems disrupt those systems and allow the remaining star to fly away, sometimes with enough velocity to escape the Galaxy.”

There is, however, one caveat. Binary stars in the center of our Galaxy will both be orbiting each other and orbiting Sgr A*. They will have two velocities associated with them. “If the velocity of the star around the binary’s center of mass happens to line up closely with the velocity of the center of mass around the supermassive black hole, the combined velocity may be large enough to escape the Galaxy altogether,” explained Zubovas.

In this case, we can’t sit around and wait to observe a supernova explosion breaking up a binary system. We would have to be very lucky to catch that! Instead, astronomers rely on computer modeling to recreate the physics of such an event. They set up multiple calculations in order to determine the statistical probability that the event will occur, and check if the results match observations.

Astronomers from the University of Leicester did just this. Their model includes multiple input parameters, such as the number of binaries, their initial locations, and their orbital parameters. It then calculates when a star might undergo a supernova explosion, and depending on the position of the two stars at that time, the final velocity of the remaining star.

The probability that a supernova disrupts a binary system is greater than 93%. But does the secondary star then escape from the galactic center? Yes, 4 – 25% of the time. Zubovas described, “Even though this is a very rare occurrence, we may expect several tens of such stars to be created over 100 million years.” The final results suggest that this model ejects stars with rates high enough to match the observed number of hypervelocity stars.

Not only do the number of hypervelocity stars match observations but also their distribution throughout space. “Hypervelocity stars produced by our supernova disruption method are not evenly distributed on the sky,” said Dr. Graham Wynn, a co-author on the paper. “They follow a pattern which retains an imprint of the stellar disk they formed in. Observed hypervelocity stars are seen to follow a pattern much like this.”

In the end, the model was very successful at describing the observed properties of hypervelocity stars. Future research will include a more detailed model that will allow astronomers to understand the ultimate fate of hypervelocity stars, the effect that supernova explosions have on their surroundings, and the galactic center itself.

It’s likely that both scenarios – binary systems interacting with the supermassive black hole and one undergoing a supernova explosion – form hypervelocity stars. Studying both will continue to answer questions about how these speedy stars form.

The results will be published in the Astrophysical Journal (preprint available here)

## THE B⚫IS: Tracking HypervElocity Blackh⚫le-Origin stars

We are THE B⚫IS! We shall be studying the nature and origins of high velocity stars stars which are, through several possible mechanisms, ejected from their home system at incredible speeds.

The most well documented of these mechanisms is called the Hills’ Mechanism. In the Hills’ mechanism a binary star system undergoes an interaction with a black hole in which one of the stars is captured by the black hole and the partner star subsequently flies off at high velocity. Such interactions have been observed to result in stars travelling with velocities of up to 1000km/s relative to the rest of the galaxy.

We shall be analysing data from GAIA and building simulations in order to model the origins of high velocity stars and build on our understanding of this fascinating phenomenon.

Today the project began in earnest. After a short delay settling a territorial dispute with the dastardly TEABAG (a neighbouring group project) interlopers we settled down at our work stations.

We have made significant progress with the simulation, with a now functional n-body simulation capable of modelling a non-binary star system, along with momentum conserving collisions resulting in an idealised confluence of mass.

Our head data analyst, Josh Smith, also made progress with plotting software TOPCAT, producing a HR diagram of the stars in our catalogue.

We are also fortunate to provide you with an exclusive interview with THE B⚫IS own coding lead, Nathan Wright. Brimming with enthusiasm, obviously eager to get back to work, we sat down to begin the interview.

‘I really enjoy fun.’

Rhys: “Hi, thanks for joining me here today for this interview.”

Nathan: “What?”

Rhys: “So you’re THE B⚫IS’ coding lead, what exactly does that entail?”

Nathan: “I’m currently opening SPYDER…”

Keenan: “No you’re not. Your screen says no internet!”

Nathan: “I’m also opening Chrome…”

Rhys: “Well it is obvious that you’re very busy, before we conclude can I get a comment on how you feel about the project in general?”

Nathan: “I really enjoy… fun.”

Join us next week for an exclusive interview with THE B⚫IS administrator, Keenan Wright, and the thrilling conclusion to the greatest dilemma of our time: Will Nathan ever connect to eduroam?

I know our readers must have been very on edge, so let me begin by allaying your doubts and assuring you that Nathan did, in fact, successfully connect to eduroam.

Tensions with TEABAG are running high, with the territorial disputes resulting in advances and retreats along the contested border. We have successfully captured an unscrupulous TEABAG spy, undoubtedly trying to steal our technology in order to fuel the forces of bourgeois reaction.

Captured TEABAG spy. Who knows what evil schemes have been enacted by this saboteur.

Today has been very fruitful with regards to progress with the project. On the coding front, Nathan has successfully implemented the Barnes-Hut algorithm, allowing our simulation to operate significantly faster by breaking it into subdivisions.

George, Antonio and Josh have successfully reduced our database of over 3 million stars to 67 viable hypervelocity stars. They plotted a graph, apparently called Carl, showing a right-ascension, declination sky-view in order to show the spread of these stars.

Carl“. This graph plots all 3 million of the stars in our database. In this graph the blue dots represent stars with a velocity over 500km/s, but these stars are too close to Sag A* to ensure that their velocity has been imparted by one of the mechanisms we are studying and not just because they have such a small orbital radius with regards to the galactic centre. The yellow dots represent stars with velocities greater than 500km/s that are sufficiently far from Sag A* that we can confidently conclude that they are hypervelocity stars which have experienced one of the mechanisms that our report is investigating.

In the meantime, me and Keenan have written the introduction of the report, summarising the 5 mechanisms which are known to give rise to high velocity stars, 3 of which can potentially give rise to hypervelocity stars.

Speaking of Keenan, I was fortunate enough to get an interview with him, included below:

“As sitting Minister of Defence… I cannot comment”

Rhys: “Thanks you for joining me for this interview”

Keenan: “Oh, is it happening now?”

Rhys: “Yes well i’m sure you’ve got a loaded schedule so lets get on with it”

Keenan: “Sure thing”

Rhys: “So what is your role within the group exactly?”

Nathan: “Is that right, is it?”

Keenan: “I hope so. It’s what i’ve been doing…”

Rhys: “So what does that entail exactly?”

Keenan: “Doing the administration stuff… Notes, schedules… etc.”

Rhys: “Right well, err, thanks for that elaboration, how do you think the group project is going overall?”

Keenan: Shrugs “Amazing, we are… except Nathan, Antonio, Rhys, Josh and George, the rest are amazing.”

Keenan: “No, get rid of that, that was off the record!”

Rhys: “…So do you have any comments on the escalating tensions with TEABAG?”

Keenan: “It would not be proper for me to comment at this time. As sitting minister of defence… I cannot comment.”

Nathan: “You’re useless Keenan”

Rhys: “Well, i’ll let you get back to your work now, i’m sure you have lots to do.”

Keenan: “Yeah, i’m currently writ-“

Rhys: “Join us next week for an exciting interview with group coordinator George Greenyer.”

Lastly, we used a random list generator to determine the order of our names on the report. As fate would have it, yours truly was selected as Author One. Accusations of possible rigging have been denied by Author One.

Update: BREAKING NEWS!

The captured TEABAG spy made an unsuccessful escape attempt . The prisoner was killed in the process.

And nothing of value was lost…

Nathan is missing. His status is unknown. Suggested possibilities range from being blown into the ocean by Storm Ciara to capture by TEABAG espionage agents. We will provide updates on this story as new information becomes available.

In the meantime, TEABAG have made several acts of aggression against our peaceful land in an attempt to avenge their deceased would-be-escapee. They have launched an attack on our Dea-Peace Star and have undergone a significant military build-up on their side of the border. The possibility of de-escalation seems increasingly unlikely.

Our benevolent Peace Star, still ablaze in the aftermath
of the brutish attack by TEABAG

On the project front, we have successfully made our own diagrams to provide additional clarity to our explanations of the Bound Scenario and Slow Intruder Scenario. These were made by yours truly on the incredibly professional application MS Powerpoint.

This magnificent diagram depicts the Bound Scenario mechanism, in which a black hole approaching a black-hole/star system destabilises the orbit in such a way that the star is ejected at high velocity. This equally magnificent diagram depicts the slow intruder scenario, in which a star passes through a black hole binary of unequal mass, and its trajectory is therefore attracted towards the more massive black hole, in this case, BH2.

Onto our data analysis. Antonio has produced the following graph of our catalogue of 3 million stars, depicted in a Gaussian distribution of their total velocities. From this graph we can calculate that the portion of stars we are considering to be hypervelocity stars (Over 500km/s) are of

10σ standard deviations from the average velocity of our catalogue.

Logarithmic Gaussian distribution of the
total velocities of our star catalogue.

We now present our exclusive interview with PI/Coordinator George Greenyer.

“Yeah. He’s dead. I mean, I definitely don’t know that, but he might be dead.
Probably.”

George: What do you want to know?

Rhys: So… Nathan is missing…

George: Yeah. He’s dead. I mean, I definitely don’t know that, but he might be dead. Probably.

Rhys: Is that a particularly big loss for the project?

George: It’s been quite nice actually, it has been much calmer and everyone is being quite nice to each other.

Rhys: So your role is PI/Coordinator, right?

George: Yes.

Rhys: What does the PI actually stand for? I’m assuming it’s not private investigator…

George: It’s actually a state secret.

Rhys: Ok. I’ll ask no more then. Can you tell us anything about what your role entails though, or is that classified as well?

George: Usually it means I yell at people and get them to do what I tell them, sometimes I help out but… mostly it’s just yelling at people.

Rhys: Have you been particularly productive so far today?

George: I have actually. I have successfully written working python code, which is madness for me.

Rhys: Yeah. I assume it’s been quite a while since you’ve used python?

George: Yeah, I tend to avoid things which cause me pain, like sharp objects, hot surfaces, and… python.

Rhys: Have you got any thoughts about the unscrupulous acts of aggression from TEABAG?

George: Well i’m looking at one right now, and I reckon I could take him!

TEABAG Interloper: If your code works you probably could…

Rhys: Alright, well I think that’s probably all for now, thanks for joining me for this interview.

George: You’re wel-

Rhys: Join me next week for an interview with ‘The All-Knowledgeable Lord President and Supreme Leader‘ Antonio Coulton.

In memoriam

I am sad to report that Nathan has been confirmed as having died in defence of the Peace Star. Fortunately Nathan’s training in the force has allowed him to come back more powerful than ever, as a force ghost.

Uh… No.

I was fortunate enough to have the opportunity to ask the freshly transparent Nathan a single question.

Rhys: Hey Nathan, can you give me a comment on what dying is like?

Nathan: Uh… No.

This new information on the realm beyond death is sure to cause many tumultuous debates in philosophical and theological communities.

Comrades, it is with a heavy heart that I must inform you that TEABAG have stooped to yet another new low. From our undercover operatives we have received intelligence proving beyond any doubt that TEABAG is manufacturing chemical weapons

Here is the incontrovertible proof that TEABAG is producing chemical weapons.

This flagrant violation of the Geneva convention so close to our border after the many unwarranted acts of aggression by TEABAG leaves us with no choice but to formally declare war against them. THE B⚫IS Central Committee does not make this decision likely, but have come, after much deliberation and debate, that it is the best path forward to ensure the prosperity and security of our peaceful nation. The civilians of TEABAG will also benefit from this our annexation of their territory will bring about great leaps forward in their quality of life and material conditions.

Apropos to the astrophysics project, myself and Keenan have discovered another high velocity star creating mechanism which we had previously overlooked. This mechanism involves the close passage of a dwarf galaxy past a larger galaxy. The interaction of tidal gravitational forces can result in a star being ejected from the dwarf galaxy into the halo of the larger galaxy as a high velocity star.

On the coding front, Nathan has been able to simulate the trajectories of 100s of suspected high velocity stars over a period of several billion years.

We now present our interview with Supreme Leader Antonio Coulton.

“If they can’t evolve fast enough, that’s their problem”

Antonio: Before we begin, I would just like to say that the alleged attack on the TEABAG medical tent has nothing at all to do with THE B⚫IS quite clearly this was an inside job as we do not have the means to carry out such an attack.

Rhys: Right well thank you for that clarification, I’m sure such information was eagerly awaited by the international community. Recent information has come to light regarding the manufacture of chemical weapons in TEABAG territory. Would you care to comment on this new intelligence?

Antonio: Of course. Such acts are not acceptable and THE B⚫IS will definitely be taking pre-emptive defensive action, including, but not limited to, espionage, propaganda campaigns and nuclear warfare.

Rhys: Do you have anything to say to allay the fears of those who worry such a war could result in the extinction of all human and teacup life?

Antonio: All humans and teacups of the world need not worry as we have only love nukes which will be spreading peace and compassion throughout the contested territory.

Rhys: Well i’m sure that will put everyone’s minds at rest. On a more positive note, the B⚫IS have recently embarked on a green initiative. Would you like to elaborate on what exactly is being done to ensure the sustainability of energy production within the nation?

Antonio: In the next ten years THE BOIS will construct 5 nuclear power stations as well as 2 new hydroelectric dams. In addition, we recently finished the construction of our nation’s first hydroelectric dam.

Rhys: Such an act surely fills the world’s hearts with hope that we can overcome the plight of impending climate disaster.

Antonio Indeed. We do love turtles.

Rhys: What are your thoughts on polar bears?

Antonio: I mean if they can’t evolve fast enough, that’s their problem.

Rhys: Nathan has recently become intangible and transparent, has this had any noticable effects on his productivity and dedication to the party line?

Antonio: Until the recent death of Nathan I never believed in ghosts, there just wasn’t a physical explanation. This is why, given the recent resurrection of Nathan as a force ghost, I will be dedicating all of my time to the research of ghosts. Nathan has now become much more productive as he no longer needs sustenance or sleep. He has successfully simulated the future trajectory of 100s of suspected high velocity stars.

Rhys: It sounds like progress on the simulation is coming along well. Do you think the project is on track to finish on time?

Antonio: Hold on, let me consult my magic eight ball.

Rhys: Ok, i’ll give you a second.

Antonio: It says ‘most likely’
Rhys: Well that’s a relief. Thanks for taking time out of your very busy schedule for this interview. I’ll let you go back to governing the country now.

Antonio: Aye, absolu-

I must apologise for the late upload of this blog update, but we have been without internet, forced to retreat into underground bunkers in order to avoid an unscrupulous attack against us by TEABAG.

On the 27th George successfully produced a graph of escape velocity against distance from the galactic centre, as seen below:

I meanwhile derived an equation to calculate the net effect of dark matter on a simulated high velocity star, using geometric arguments and the following diagram to produce the subsequent equation.

Note that this is the final version of the equation produced on 05/03/2020. The one produced on 27/02/2020 had some which we have since corrected.

Nathan successfully managed to recreate the production of a high velocity star through the Hills’ mechanism in his code.

Finally, I interviewed Josh, as seen below.

Rhys: Thanks for joining me today.

Josh: Yeah, anytime.
Rhys: So how does it feel to be reaching the end of labs?
Josh: Stressful.
Rhys: Are you not relieved that you won’t have to come in for 7 hours anymore?
Josh: Yeah i’ll be relieved when it’s over, but i’ve not had time to get started on my section of the report. So it’s… not very good.

Rhys: So what exactly is your role within the group?
Josh: I am Error Man!
Rhys: And what type of superpowers does such a role bestow?
Josh: Err… what does that mean?
Rhys: … Nevermind I guess… Any general comments on the project?

Josh: I get frustrated that things aren’t moving as they have been, and ‘certain’ people haven’t been putting their equations in the data sheet
George: what are you looking at me for?
Josh:
Rhys: The conflict with teabag appears to have cooled down, any thoughts?
Josh: I try and stay out of these matters, i’m a conscientious objector. I am a man of peace.
Rhys: Does your principle of non-violence ever conflict with the obligation to use your error analysis superpowers for the greater good?
Josh: These are just words, they have no meaning.
Rhys: I didn’t realise you had transcended the medium of conversation, perhaps I too shall have to invest in the magic of error propagation

Rhys: So how do you respond to the allegations against you of revisionism and deviation form the party line?
Josh: No comment (leaves)
Rhys: I think that speaks for itself. Join me next week, for an the most exciting interview guest yet, Myself!

At the conclusion of this interview the air-raid sirens warned us of an impending TEABAG attack and we were forced to retreat to the nuclear bunkers.

Today we were finally able to exit the bunkers, with the radiation having reduced to bearable levels. In response to TEABAG’s attack against us we have responded in kind. Their land has now been reduced to rubble. The handful of survivors have been vassalised and we are now proud to announce the birth of a new nation THE DEMOCRATIC PEOPLE’S REPUBLIC OF TEAB⚫IS.

Meanwhile I have made corrections to the equation derived in the last update, which perhaps took a tad longer than it should have done.

Nathan has been simulating a wide array of stars using our now finalised code, with over 1000 stars being simulated as I type this.

And finally, here is our long awaited interview with myself:

Rhys: Hi Rhys, thank you for joining me here.

Rhys: To be honest I had somewhere else I wanted to be but I can’t seem to get away from you.

Rhys: So what is your role in the group?

Rhys: And what does that entail?

Rhys: I have to write a large portion of the report. I also have to write this crappy blog…

Rhys: Crappy?! I’ll have you know this blog has been reasonably well received!

Rhys: I think that’s more a comment on people’s low standards rather than the quality of the blog…

Rhys: I don’t really need all this negativity to be honest… Lets change topic. So… the war with TEABAG is over, THE B⚫IS have annexed their territory and absorbed the survivors into their populace. What are your thoughts on this?

Rhys: It’s a mixed bag. On the one hand a dark period in our short history is now behind us. However, I question the wisdom of the Supreme Leader‘s decision to immediately declare war against BAHAMAS. I think we could have done with a period of peace in order to rebuild our productive forces. Don’t tell him I said that though.

Rhys: Don’t worry, my lips are sealed. To be honest, I’m inclined to agree. With that I think the interview is finished. Thank you for joining me here today!