What is the long term fate of the gas giants?

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If I'm not mistaken, it is believed that the reason for such turbulent weather on the 4 outer gas giant planets is that the internal pressure is so great that it is generating heat, which is causing convection, which causes extreme weather.

Will these planets forever generate heat, or at some point will they freeze up?

What will Jupiter look like a trillion years from now?

The timescale on which Jupiter cools is reasonably well understood and predicted by the current generation of evolutionary models.

Jupiter's luminosity is provided mostly by gravitational contraction. For a planet that only contains gas governed by the perfect gas law, the appropriate timescale for this contraction (or indeed for the luminosity to fall significantly) is given by the Kelvin Helmholtz timescale. $$au = eta frac{GM^2}{RL},$$ where $M$ and $R$ are Jupiter's mass and radius and $L$ is its current power output (or luminosity), and the parameter $eta sim 1$. This timescale is a few $10^{11}$ years.

However, giant planets like Jupiter are not governed by perfect gas laws. The gas in the centre of Jupiter is dense enough that electrons become degenerate. Degenerate electrons fill the available energy levels up to the Fermi energy. Their consequent non-zero momenta of the electrons exerts a degeneracy pressure that is independent of temperature. As a result, the rate of contraction slows and the release of gravitational potential energy slows; the planet is able to cool and remain in hydrostatic equilibrium without the same degree of contraction.

One can express this change using the $eta$ parameter. For Jupiter $eta simeq 0.03$ (Guillot & Gautier 2014) - i.e. the timescale for the luminosity to fade is 30 times quicker than the naive Kelvin-Helmholtz time and Jupiter's luminosity will scale as the reciprocal of its age and will fall by a factor of a few in $10^{10}$ years. In a trillion years, the luminosity of Jupiter will be lower than it is now by roughly a factor of 250.

From what I know, the heat was mostly generated when the gas giants are created. Some of this was from the friction caused by internal pressure. However, this heat is not being generated anymore, as it was only generated as matter fell into the planet.

They presumably do generate heat from radioactive elements in the core (though nobody has ever been down and checked if there are any :P), and will also receive a 'boost' from solar heating.

Over time, however, each heat source will diminish. The latent heat from birth will be dissipated into space in the form of radiation, the radioactive elements will decay, and the star it's orbiting will die off.

So I guess that Jupiter will no longer have its dramatic weather in a trillion years.

In "one trillion" years Jupiter's fate will be affected by how violent our Sun becomes when it transforms in Red Giant, 5000 million years (5Gy) from now.

With our Sun being so big and brilliant, it will heat Jupiter quite a lot more than now. But also the mass lose will make Jupiter spiral out towards a bigger orbit, while capturing some extra mass.

So in "one trillion" years Jupiter will be a bigger, colder and denser (as well pointed by Rob Jeffries in his answer), more external planet around a white dwarf.

Ask Ethan: Is There a Way To Save Our Galaxy From Its ‘Inevitable’ Fate?

Galaxies that have formed no new stars in billions of years and have no gas left inside them are . [+] considered 'red-and-dead.' A close look at NGC 1277, shown here, reveals that it may be the first such galaxy in our own cosmic backyard. Our galaxy will follow suit, and the stars will die out and then be ejected, leading to the end of our Local Group as we know it.

NASA, ESA, M. Beasley (Instituto de Astrofísica de Canarias), and P. Kehusmaa

Our Universe, as it exists today, puts us in an incredibly privileged position. Had we come into being just a few billion years earlier, we’d be unable to detect the existence of dark energy, and thus we’d never know the true fate of our Universe. Similarly, were we born tens of billions of years in the future — just a few times the present age of the Universe — our local group would be just one giant elliptical galaxy, with no other galaxies visible beyond our own for hundreds of billions of light-years. As far as we can tell, our Universe is dying, and a “heat death” awaits us. There may be no way to stop it, but could we somehow, with an advanced enough technology, delay it? That’s the question of Patreon supporter John Kozura, who wants to know:

“After reading your posting about the natural death of the Universe as we passively watch, I got to thinking: what could an extremely advanced, Type III level civilization could proactively do to make a galaxy/local cluster run "efficiently" for longer to their benefit. are there ways we could act as a sort of large scale Maxwell's demon to manage entropy and efficiently control the energy budget of the galaxy?”

If we do nothing, our fate is sealed. But even within the laws of physics, we might be able to save our galaxy for longer than any other one in the Universe. Here’s how.

A series of stills showing the Milky Way-Andromeda merger, and how the sky will appear different . [+] from Earth as it happens. This merger will occur roughly 4 billion years in the future, with a huge burst of star formation leading to a red-and-dead, gas-free elliptical galaxy: Milkdromeda. A single, large elliptical is the eventual fate of the entire local group. Despite the enormous scales and numbers of stars involved, only approximately 1-in-100 billion stars will collide or merge during this event.

NASA Z. Levay and R. van der Marel, STScI T. Hallas and A. Mellinger

If you want to save the Universe, you first have to understand what you’re saving it from. Right now, there are some

400 billion stars in the Milky Way, plus even more in our neighboring galaxy, Andromeda. Both us and our nearest large neighbor are still forming stars, but at a much lower rate than we did in the past. In fact, the total star formation rate of the galaxies around today is about a factor of

20 smaller than it was at its peak, some 11 billion years ago.

However, both the Milky Way and Andromeda have copious amounts of gas left in them, and we’re on a collision course.

29 Intelligent Alien Civilizations May Have Already Spotted Us, Say Scientists

Meanwhile all the other galaxies, galaxy groups, and galaxy clusters continue to accelerate away from us. At that point, star formation in our future home, Milkdromeda, will be merely a trickle, but we’ll have more stars present within it than ever before, numbering in the trillions.

The starburst galaxy Messier 82, with matter being expelled as shown by the red jets, has had this . [+] wave of current star-formation triggered by a close gravitational interaction with its neighbor, the bright spiral galaxy Messier 81. Although starbursts will form tremendous numbers of new stars, they will also deplete the gas present, preventing large numbers of future generations of stars.

NASA, ESA, The Hubble Heritage Team, (STScI / AURA) acknowledgement: M. Mountain (STScI), P. Puxley (NSF), J. Gallagher (U. Wisconsin)

If we do nothing, the stars that come into existence will simply burn out once enough time passes by. The most massive stars only live for a few million years, while stars like our Sun might have a lifetime more like

10 billion years. But the least massive stars — the red dwarfs that barely have enough mass to ignite nuclear fusion in their cores — might continue their slow burning for as many as

100 trillion (10 14 ) years. So long as there’s fuel in their cores to burn, or enough convection occurring to bring new fuel into the core, nuclear fusion will continue.

Given that 4 out of every 5 stars in the Universe is a red dwarf, we’ll have lots of stars for a very long amount of time. Given that there may be even more brown dwarfs out there than stars, where brown dwarfs are a little bit too low in mass to fuse hydrogen into helium the way normal stars do, and that some 50% of all stars are in multi-star systems, we’ll have inspirals and mergers of these objects for even longer periods of time.

Whenever two brown dwarfs merge together to form a massive enough object — more than about 7.5% the present mass of our Sun — they’ll ignite nuclear fusion in their cores. This process will be responsible for the majority of stars in our galaxy until the Universe is hundreds of quadrillions (

The inspiral and merger scenario for brown dwarfs as well-separated as the systems we've already . [+] discovered would take a very long time due to gravitational waves. But collisions are quite likely. Just as red stars colliding produce blue straggler stars, brown dwarf collisions can make red dwarf stars. Over long enough timescales, these 'blips' of light may become the only sources illuminating the Universe.

MELVYN B. DAVIES, NATURE 462, 991-992 (2009)

But once the Universe reaches that age, another process will come to dominate: gravitational interactions between the stars and stellar remnants in our galaxy. Every once in a while, two stars or stellar corpses will pass close by one another. When this occurs, they will either:

• interact with each other but both remain in the galaxy,
• collide and merge together,
• tidally disrupt one or both members, potentially getting torn apart in a cataclysmic tidal disruption event,
• or — and this is the most interesting possibility — they could cause one member to become more tightly gravitationally bound to the galactic center, while the other member becomes more loosely bound, or even ejected entirely.

That last possibility, on long timescales, will dominate the fate of our galaxy. It might take

10 20 years, but that’s the point where practically all the stars and stellar remnants will either be sent into stable orbits that will decay via gravitational radiation, inspiraling around the galactic center until everything merges into one enormous black hole, or ejected into the abyss of intergalactic space.

As a black hole shrinks in mass and radius, the Hawking radiation emanating from it becomes greater . [+] and greater in temperature and power. Once the decay rate exceeds the growth rate, Hawking radiation only increases in temperature and power. As black holes lose mass due to Hawking radiation, the rate of evaporation increases. After enough time goes by, a brilliant flash of 'last light' gets released in a stream of high-energy blackbody radiation that favors neither matter nor antimatter.

Beyond that time, orbital decay from gravitational radiation and black hole decay from Hawking radiation are the only two processes that will matter. An Earth-mass planet in an Earth-sized orbit around a stellar remnant with the mass of our Sun will take around

10 25 years to spiral in so that they merge the most massive black hole in our galaxy, while a black hole of the mass of our Sun will take around

10 67 years to evaporate. The most massive black hole in the known Universe might take upwards of

10 100 years to fully evaporate, but that’s pretty much all we’ll have to look forward to. In a sense, if we take no further interventions, our fate is sealed.

But what if we wanted to avoid this fate, or at least push it out into the future as far as possible? Is there anything we could do about any or all of these steps? It’s a big question, but the laws of physics allow for some truly incredible possibilities. If we can measure and know what the objects in the Universe are doing to an accurate enough precision, then perhaps we can manipulate them in some clever way to keep things going a little bit longer.

The key to making it happen is to start early.

If a large asteroid strikes Earth, it has the potential to release an enormous amount of energy, . [+] leading to local or even global catastrophes. At

450 meters long along its long axis, asteroid Apophis could release about 50 times the energy of the Tunguska blast: minuscule compared to the asteroid that wiped out the dinosaurs, but many times larger than even the most powerful atomic bomb detonated in history. The key to stopping an asteroid collision is early detection and early action to begin deflection procedures.

Think about an analogous problem: what would we do if we discovered an asteroid, comet, or other significantly massive object were on a collision course for Earth? You’d ideally want to deflect it, so that it would miss our planet.

But what’s the best, most efficient way to do this? It’s to “correct” the course of this body — not the Earth, but the lower-mass object that’s headed towards us — as early as possible. A tiny change in momentum early on, which arises from a force that you’d exert on this body over a duration of time, will deflect its trajectory by a much more significant amount than that same force will even a tiny bit later. When it comes to gravitational dynamics, an ounce of prevention is much more effective than a pound of cure a little bit later.

This is why, when it comes to planetary defense, the most important things we can do are:

• identify and track every object above a certain hazardous size as early as possible,
• characterize its orbit as exquisitely precisely as we can,
• and understand which objects it will interact with and pass close to over time, so that we can project its trajectory accurately very far into the future.

This way, if something’s going to hit us, we can intervene at the earliest stages possible.

The NEXIS Ion Thruster, at Jet Propulsion Laboratories, is a prototype for a long-term thruster that . [+] could move large-mass objects over very long timescales.

There are multiple strategies we can take to deflect an object by a small amount over a long period of time. They include:

• attaching a “sail” of some sort to the object we want to move, reliant on either solar wind particles or the outward flux of radiation, to change its trajectory,
• creating a combination of ultraviolet lasers (to ionize atoms) and a strong magnetic field (to funnel those ions in a particular direction) to create a thrust, thus changing its trajectory,
• attaching a passive engine of some sort to the object in question — like an ion thruster — to slowly accelerate a solid body in the desired direction,
• or to simply move other, smaller masses near the vicinity of the object we want to deflect, and letting gravity take care of the rest, like a game of cosmic billiards.

Different strategies might be more or less effective for different objects. The ion thruster might work best for asteroids, while the gravitational solution might be absolutely necessary for stars. But these are the types of technologies that can generally be used to deflect massive objects, and that’s what we’d want to do to control their trajectories in the long run.

At the centers of galaxies, there exists stars, gas, dust, and (as we now know) black holes, all of . [+] which orbit and interact with the central supermassive presence in the galaxy. On long enough timescales, all such orbits will decay away, leading to consumption by the largest remaining mass. At the galactic center, this should be the central supermassive black hole in our Solar System, that should be the Sun. Small changes induced by us in a particular direction, however, could extend those timescales by multiple orders of magnitude.

What I can envision in the far, far future, is a network of a combination of these that find and seek out solid masses throughout the Universe — asteroids, Kuiper belt and Oort cloud objects, planetesimals, moons, etc. — all of which have their own atomic clocks on board, and strong enough radio signals to communicate with one another over large distances.

I can envision that they would measure the matter within our galaxy — the gas in the Milky Way, the stars and stellar remnants in Milkdromeda, the “failed stars” that will merge to form subsequent stars in the late-time Universe, etc. — and they could calculate which trajectories they would need to take in order to maintain the maximum amount of baryonic (normal) matter within our galaxy.

If you can shepherd these objects into stable orbits for longer, so that the process of violent relaxation — where low-mass objects get kicked out over time while higher-mass objects sink to the center — it would be a way to maintain the matter that we have for longer, and that would enable our galaxy to survive, in a sense, for much longer periods of time.

The ancient globular cluster Messier 15, a typical example of an incredibly old globular cluster. . [+] The stars inside are quite red, on average, with the bluer ones formed by the mergers of old, redder ones. This cluster is highly relaxed, meaning the heavier masses have sank to the middle while the lighter ones have been kicked into a more diffuse configuration or ejected entirely. This effect of violent relaxation is a real and important physical process, but it may be controllable with enough large masses in a network with appropriate thrusters attached.

You can’t stop entropy from increasing, but you can prevent entropy from increasing in a particular way by performing work in a particular direction. So long as there’s energy to extract from your environment, which you can do so long as stars and other sources of energy are close by, you can use that energy to direct in what ways your entropy increases. It’s sort of like how, when you clean your room, the overall entropy of the “you + room” system increases, but the disorder in your room goes down as you put energy into it. It was your inputs that changed the situation of the room, but you paid the price yourself.

Similarly, the shepherding probes attached to various masses would pay the price in terms of energy, but they could keep masses in a much more stable long-term configuration. This could lead to:

• more gas remaining within the Milky Way to participate in future generations of star-formation,
• more stars and stellar remnants remaining in Milkdromeda and fewer large masses falling in towards the central black hole in our galaxy,
• and longer lifetimes for stars and stellar remnants, increasing the amount of time that mergers and the ignition of new stars can occur.

When two brown dwarfs, far into the future, finally do merge together, they will likely be the only . [+] light shining in the night sky, as all other stars have gone out. The red dwarf that results will be the only primary light source left in the Universe at that time.

user Toma/Space Engine E. Siegel

In theory, there’s a way to maximize the duration that we’ll still have stars (and sources of power) in whatever’s left of our Local Group very far into the future. By tracking and observing these clumps of matter floating through space, we can calculate — or have artificial intelligence calculate — the optimal set of trajectories to deflect them onto, maximizing the amount of mass, the number of stars, and/or the energy flux of starlight within our future galaxy. We might be able to increase the duration over which we’ll have usable energy, stars with rocky planets around them, and even, potentially, life, by factors of 100 or even greater amounts.

You cannot ever defeat the second law of thermodynamics, as entropy will always increase. But that doesn’t mean you simply have to give up, and let the Universe run amok in whatever direction nature would take it. With the right technology, we can minimize the rate at which stellar ejections occur and maximize the total number of stars that will ever form, as well as the duration that they’ll persist for. If we can survive our technological infancy and truly become a spacefaring, technologically advanced civilization, we might be able, in a sense, to save our galaxy in a way that no other galaxy is ever saved. If a super-intelligent civilization is out there, this might be the evidence they’d look for to know, even from across the now-unreachable Universe, that they truly weren’t alone.

Fannie-Freddie Fate a Mystery After High Court Market Shock

(Bloomberg) -- In one fell swoop, the Supreme Court crushed Fannie Mae and Freddie Mac shareholders and gave President Joe Biden carte blanche to rewrite the rules for the U.S.’s massive housing market.

Left unanswered was the same question that’s befuddled Washington for more than a decade: Will anyone ever figure out what to do with Fannie and Freddie, which backstop a whopping $5.7 trillion of mortgages? The high court’s decision Wednesday largely shot down investors’ claims that Obama era regulators exceeded their authority when they decided to send nearly all of Fannie and Freddie’s profits to the U.S. Treasury -- a ruling that could save the federal government more than$100 billion. The justices also made clear that the president can remove the head of the Federal Housing Finance Agency, Fannie and Freddie’s overseer.

Within hours, the White House said Biden would oust FHFA Director Mark Calabria, a libertarian economist who was installed by former President Donald Trump. And Capitol Hill Democrats started demanding that the FHFA refocus Fannie and Freddie on making housing more affordable -- a top priority for progressives.

Read More: Fannie-Freddie Ruling Marks Latest Blow to Funds in Doomed Trade

Once the dust settled, Fannie and Freddie shares had both plunged more than 32%, the biggest one-day slide for the companies since February 2017. The bleeding was even worse for various share classes of preferred stock owned by major hedge funds, triggering losses that in some cases exceeded 60%.

Among firms likely hurt by the high court’s decision were Paulson & Co., Pershing Square Capital Management and Fairholme Funds Inc., which have sought for years to get their hands on Fannie and Freddie’s profits.

With a new FHFA appointee, Biden will in effect be able to control the standards and cost of loans backed by Fannie and Freddie, which make up around half of the mortgage market.

In a statement released late Wednesday, the FHFA said the White House had named Sandra Thompson the regulator’s acting director. She had been the FHFA’s deputy director of the division of housing mission and goals. Biden hasn’t nominated a permanent successor to Calabria and any candidate would have to be confirmed by the Senate.

While Calabria had moved to shrink Fannie’s and Freddie’s footprint, many housing analysts expect Biden to use Fannie and Freddie to make loans cheaper and easier to get for minority groups and less-well-off borrowers, who historically have found it more difficult to buy a home.

In addition to borrowers, those decisions affect lenders, mortgage-bond investors, and issuers of privately-backed mortgages that compete with Fannie and Freddie.

“Today’s decision gives President Biden the opportunity to make sure that we have an FHFA director who is committed to addressing the housing needs of renters and homeowners, and to making our housing system work for everyone,” Senate Banking Committee Chairman Sherrod Brown, an Ohio Democrat, said in a statement.

Read More: Biden to Oust Fannie-Freddie Regulator After Court Ruling

Fannie and Freddie are crucial to housing because they buy loans from lenders and package them into bonds while guaranteeing payment to investors if homeowners default. The process keeps the mortgage market humming and ensures borrowing rates remain low.

Fannie and Freddie got into trouble when the housing market tanked in the run-up to the Great Recession, prompting the government to take them over and rescue them with $187.5 billion in taxpayer funds. The firms have since become profitable again, paying out billions of dollars in dividends to the Treasury. Determining the future of companies, including how they might function outside of U.S. control, is the biggest policy decision remaining from the 2008 financial crisis. The shareholders’ loss before the Supreme Court removes any pressure, at least for now, for Biden to break from the status quo, said Jim Vogel, an analyst at FHN Financial. That means Fannie and Freddie could remain in federal conservatorship for the foreseeable future, a situation that the Trump administration tried and failed to bring to an end. Investors had hoped that a win at the Supreme Court would put pressure on Biden to settle the cases and release the companies from government control. Read More: Fannie and Freddie Shareholders Mostly Lose Again The ruling “appears to lay to rest many of the lingering questions and ‘what-ifs’ surrounding how long Fannie and Freddie could continue their status as a ward of the federal government,” Vogel said. “The status quo can continue as long as the administration and Congress would like.” Fannie and Freddie shareholders still have on-going lawsuits in other cases proceeding under different legal theories that they plan to continue fighting. “The SCOTUS decision does not address claims by shareholders for just compensation under the Takings Clause or for damages for breach of their shareholder contracts,” Boies Schiller Flexner attorney Hamish Hume, who represents investors in another case, said in an email “We continue to vigorously litigate those claims in lower courts and believe they will ultimately prevail.” Whatever path the Biden administration takes on Fannie and Freddie, Compass Point Research & Trading’s Isaac Boltansky doesn’t anticipate major changes to housing finance. “While our nation’s mortgage-finance system is a Frankenstein’s monster, and it is far from perfect, it continues to function well,” Boltansky said in an email. “Congress has neither the interest nor the capacity to fix something that is not broken.” Natural Gas and Its Fate in the COVID-19 World Could natural gas prices suffer the same fate as crude oil’s descent to below zero? What was once considered a useless byproduct of crude oil production, natural gas has turned into a vital energy source as nations transition to the so-called bridge fuel. Like everything else in this economy, the commodity has fallen victim to the Coronavirus pandemic. Since crude prices crashed to below zero for the first time in its history in April, analysts have been pondering if natural gas could suffer the same fate in the coming months. Will prices slump to negative territory? Look at the data. A Case of Supply and Demand Over the last five years, U.S. natural gas production has skyrocketed as companies took advantage of prices that peaked at about$6. In 2019, output topped 100 billion cubic feet, and it looked like it was only going to climb higher due to enormous global demand. But then COVID-19 happened, triggering an international supply glut and an immense North American and European supply build.

Recently, two reports were published that offered some insight into the state of natural gas today.

The first was the Energy Information Administration’s (EIA) weekly stockpile reading that showed an increase of 93 billion cubic feet in domestic inventories for the week ending June 5. This brought the total level of stockpiles to 2.807 trillion cubic feet, up 748 billion cubic feet from last year, and 421 billion cubic feet above the five-year average. The EIA is also predicting a 16% decrease in output.

The second was an assessment from the International Energy Agency (IEA). It forecast that worldwide consumption would plunge 4% this year, more than double the last significant drop during the 2008 financial crisis. This would represent the largest decline since the prevalence of natural gas in the second half of the 20 th century. The IEA also lowered its global demand projection for 2025, from 1.8% to 1.5%. Fatih Birol, the IEA’s executive director, summarized the situation in the report:

“The record decline this year represents a dramatic change of circumstances for an industry that had become used to strong increases in demand. The Covid-19 crisis will have a lasting impact on future market developments, dampening growth rates and increasing uncertainties.”

America’s energy giants are slowly adapting to the situation. The Baker Hughes natural gas rig count has slipped below 80, while U.S. firms are curtailing operations and laying off thousands of workers. But it could take longer than expected to rebalance the market since it is estimated to be oversupplied by 20% under current conditions. But do not be dismayed. There is plenty of hope due to economies reopening, hotter temperatures, and higher electricity generation.

Subzero or Hot Air?

The $64,000 question – or is it -$64,000? – is if natural gas prices could mirror crude oil from April and nosedive below zero. This specter hangs over the industry, but could it happen?

Last month, the sector got a taste of what it would be like in this economy. The next-day natural gas prices at the Waha Hub in the Permian basin in West Texas slumped below zero for the second time in a month. Producers and investors are now waiting with bated breath to see if it could explode industrywide.

At the beginning of May, the billionaire chairman of China’s ENN Energy warned that prices could turn negative because of maximizing storage capacities. Wang Yuso refrained from naming any market or benchmark, but he did think these prices would be temporary.

Jonathan Stern, a senior research fellow at the Oxford Institute of Energy Studies, recently told Reuters that if natural gas prices became negative, it would be short-lived and serve as a wakeup call for suppliers. Stern believes any situation involving subzero pricing would happen before storages max out.

Not everyone is convinced. The Bank of America recently raised its natural gas price forecast for next year from $2.45 to$2.75. BofA analysts cited accelerating production cuts. Shell CEO Ben van Beurden is confident that the industry is making the necessary adjustments and that it would return to balance next year. He told Bloomberg:

“We will obviously flex our investment program to be aligned with where we believe the sector will go, but the profitability of the business and the outlook of this business is going to be as good as what you saw before the pandemic.”

Year-to-date, prices are down more than 20% to around \$1.75 per million British thermal units (btu).

The Comeback Kid

America’s ascent to the top of the energy food chain has been nothing short of remarkable, proving a handful of essential elements. The first is that it highlights Saudi America’s ingenuity – spotlighting the power of the free market. The second is that it shows what happens when the federal government moves even one step out the door. Thirdly, the peak oil crowd keeps getting it wrong. The final benefit is that it triggered the militant climate alarmists who only want wind farms and solar power. Natural gas behaves in a cyclical pattern like other commodities. Prices are down now, but they will inevitably make a comeback and help pad the bottom line for producers and investors alike. As more markets transition to this fuel, natural gas will be supreme again.

German

Autor:innen: Sandip V George , Sneha Kachhara , Ranjeev Misra , and G. Ambika

Institut des Erstautors: University Medical Center Groningen (UMCG), Department of Psychiatry, Interdisciplinary Center Psychopathology and Emotion regulation (ICPE), Niederlande

Status: Veröffentlicht in Astronomy & Astrophysics [ open access]

Wenn ich persönlich einen astronomischen Wunsch frei hätte, dann würde ich wünschen, dass Beteigeuze noch zu meinen Lebzeiten zur Supernova wird.

Beteigeuze kann jeden Moment explodieren, zwischen jetzt und in 100 000 Jahren. Das ist für Astrophysiker:innen fast dasselbe wie “jetzt”. Natürlich sind die Chancen, dass ich dieses große Ereignis miterleben werde, gemessen an der menschlichen Lebensspanne, gering.

Nichtsdestotrotz sorgte Beteigeuze im Jahr 2019 für Aufsehen, als er plötzlich so stark abdunkelte, dass der Unterschied mit bloßem Auge erkennbar war (siehe Abb. 1). Später wurde er kontinuierlich wieder heller.
Die Erklärung, dass Staub einen Teil des Lichts des Sterns in unsere Richtung abblockte, hat sich seitdem etabliert.

Abb. 1: Beteigeuzes normale Helligkeit (links) und seine Verdunkelung Anfang 2020 (rechts) (Quelle: H. Raab, Wikimedia)

Große Sterne, kurzes Leben

Verglichen mit unserer Sonne ist Beteigeuze wirklich ein Riese. Sein Radius ist irgendwo zwischen 600 und 880 Mal größer als der der Sonne, und wäre Beteigeuze an der Stelle der Sonne, würde sich die Umlaufbahn des Jupiters immer noch unterhalb seiner Oberfläche befinden.

Aber obwohl er unseren Heimatstern in fast allen Aspekten übertrifft, gibt es eine Kategorie, in der unsere Sonne die Nase vorn hat: das Alter. Beteigeuze ist gerade einmal 8 Millionen Jahre alt und gilt bereits als Fall für den stellaren Sensenmann. Zum Vergleich: Die Sonne existiert seit rund 4 Milliarden Jahren und befindet sich vermutlich etwa in der Halbzeit ihres Lebens.

Die Größe von Beteigeuze führt dazu, dass der für die Kernfusion in seinem Inneren notwendige Brennstoff schneller verbraucht ist und lässt ein gewaltsames Ende vorausahnen, wenn seine massiven Gravitationskräfte den Kampf gegen die Strahlungsenergie gewinnen und er kollabiert. Dieser gewaltsame Tod von massereichen Sternen wie Beteigeuze wird als Supernova bezeichnet.

Vorwarnung

Die Autor:innen des heutigen papers haben einen Blick auf die langfristige Entwicklung von Beteigeuze geworfen, vom Beginn der modernen Beobachtungen des Sterns in den 1980er Jahren an.

Frühwarnungen für eine bevorstehende Veränderung innerhalb eines dynamischen Systems (Sterne sind keine unveränderlichen Objekte, sie sind ständigen Veränderungen und inneren Bewegungen unterworfen) lassen sich erkennen, wenn man lange Zeit die Lichtkurve eines Objekts vor einem Ereignis, in diesem Fall der Verdunkelungsepisode, beobachtet.
Frühere Arbeiten haben darauf hingewiesen, dass, wenn Staub dafür verantwortlich wäre, ein Überschuss an infrarotem Licht nahe der Verdunkelung sowie eine Verringerung des polarisierten Lichts aufgrund des Durchgangs durch den Staub hätte beobachtet werden müssen. Beide Bedingungen konnten nach detaillierten Messungen und Analysen nicht erfüllt werden.

Jedes dynamische System kann in mehreren möglichen Zuständen existieren. Diese Zustände entwickeln sich nach einem bestimmten Muster und existieren für eine bestimmte Parameterkombination. Bestimmte Übergänge zwischen den Zuständen – kritische Übergänge genannt – bedeuten große Änderungen im dynamischen Verhalten des Systems. Sie können durch nur kleine Veränderungen der Parametern des Systems verursacht werden.

Die Autor:innen argumentieren, dass das Verdunkelungsereignis aufgrund eines kritischen Übergangs in der Pulsationsdynamik von Beteigeuze aufgetreten sein könnte. Das bedeutet, dass die Natur der Systemdynamik eine drastische Änderung erfuhr.

Zeiten des Wandels

Andere Arbeiten haben gezeigt, dass mehrere Größen einer Zeitreihe (wie z. B. die Lichtkurve) die auf einen kritischen Übergang des Systems zugeht, zunehmen. Drei dieser Größen, die in dieser Arbeit untersucht werden, sind die Autokorrelation, die Varianz und die sogenannte Detrended Fluctuation Analysis (DFA). Wenn die Veränderung der Helligkeit von Beteigeuze tatsächlich auf einen kritischen Übergang in der Pulsationsdynamik zurückzuführen ist, dann sollte sich das in diesen Größen niederschlagen.

Die Autokorrelation ist, einfach ausgedrückt, die Ähnlichkeit eines zu verschiedenen Zeiten beobachteten Signals als Funktion des zeitlichen Abstands dazwischen. Dies ermöglicht die Herausarbeitung von sich wiederholenden Mustern, wie z. B. periodischen Signalen, die sonst vom Rauschen überdeckt werden würden.
Die Varianz misst die Streuung der Datenpunkte um ihren Mittelwert.
Die DFA wandelt die Daten zunächst in eine kumulative (also jede Messung wird zur vorherige addiert) Amplitudenzeitreihe um. Der quadratische Mittelwert der Abweichung ist die Schwankung des linearen Trends und sollte als Potenzgesetz über die Zeit ansteigen. Der Exponent hiervon wird als Hurst-Exponent bezeichnet.

Die Untersuchung dieser drei Quantoren wurde auch in Bereichen außerhalb der Astronomie angewandt, z. B. in der Ökologie, den Ingenieurwissenschaften und der Psychiatrie. Die Autoren der heutigen Arbeit kommen also aus verschiedenen Bereichen, darunter Medizin, komplexe Systeme, Physik und Astrophysik, um ihr Fachwissen optimal einzusetzen.

Da es in den Daten zwischen 1980 und 1990 eine große Anzahl von Lücken gibt, werden die Trends für die Autokorrelation, Varianz und ⍺ für die Daten ab 1990 analysiert. Die resultierenden Diagramme sind in Abb. 2 dargestellt.

Abb. 2: Autokorrelationsfunktion, Varianz und Hurst-Exponent der Lichtkurve von Beteigeuze über die Zeit. In grau sind Messungen vor 1990, in grün nach 1990 eingezeichnet.
(Abb. 1 im heutigen paper)

Für alle drei Quantoren steigen die Werte über die Zeit an, bevor die Verdunkelungsepisode beginnt. Dies impliziert, dass ein dynamischer Übergang innerhalb von Beteigeuze zu der abnehmenden und anschließend zunehmenden Helligkeit 2019/2020 führte.
Andere Arbeiten weisen auf ein weiteres mögliches Verdunkelungsereignis Mitte bis Ende der 1980er Jahre hin, was die Änderung des allgemeinen Trends der drei Größen zu diesem Zeitpunkt erklären könnte.

Weitere Analysen, die unter anderem auf der Anzahl der sich wiederholenden Zustände des Systems basieren, wie deterministisch die Dynamik zu sein scheint und das Ausmaß der laminaren (d.h. nicht-turbulenten) Phasen, wurden von den Autoren durchgeführt. Diese Maße zeigen ebenfalls einen allmählichen Anstieg bis zur Verdunkelungsphase.

Eine neue Ära für Beteigeuze

Die Autor:innen kommen zu dem Schluss, dass die Signatur der bevorstehenden Veränderung im dynamischen System von Beteigeuze schon lange vor dem Ereignis zu beobachten war.

Es spricht einiges dagegen, dass eine Staubwolke für die Verdunkelung von Beteigeuze verantwortlich ist, während auch bereits gezeigt wurde, dass die effektive Temperatur des Sterns während des Ereignisses nicht signifikant gesunken ist, was höchstwahrscheinlich ein konvektionsgetriebenes Verdunkeln, also eine vorübergehende Abkühlung der Oberfläche, ausschließt.

Die Autoren betonen, dass die letzte verbleibende Option eine Änderung in der Pulsationsdynamik von Beteigeuze ist, die die Helligkeitsänderung 2019-2020 verursacht.
Es ist noch nicht eindeutig bewiesen, was zur Verdunkelung geführt hat, aber die Autor:innen erwähnen, dass ein solcher kritischer Übergang dauerhafte Veränderungen für das System bedeuten würde, die in der Zukunft nachweisbar wären. Eine kontinuierliche Beobachtung von Beteigeuze könnte uns also wichtige neue Informationen liefern und helfen, dieses Rätsel zu lösen.

Beteigeuze ist der 10. hellste Stern an unserem Nachthimmel, also leicht zu erkennen. Ich würde vorschlagen, ihn im Auge zu behalten. Nur für den Fall der Fälle.

Astrobite korrekturgelesen von Alex Gough
Bildquellen: NASA / ESA / E. Wheatley / STScI, H. Raab (Wikimedia), heutiges paper

At Last, Scientists Have Found The Galaxy's Missing Exoplanets: Cold Gas Giants

There are four known exoplanets orbiting the star HR 8799, all of which are more massive than the . [+] planet Jupiter. These planets were all detected by direct imaging taken over a period of seven years, with the periods of these worlds ranging from decades to centuries.

Jason Wang / Christian Marois

In the early 1990s, scientists began detecting the first planets orbiting stars other than the Sun: exoplanets. The easiest ones to see had the largest masses and the shortest orbits, as those are the planets with the greatest observable effects on their parent stars. The second types of planets were at the other extreme, massive enough to emit their own infrared light but so distant from their star that they could be independently resolved by a powerful enough telescope.

Today, there are over 4,000 known exoplanets, but the overwhelming majority either orbit very close to or very far from their parent star. At long last, however, a team of scientists has discovered a bevy of those missing worlds: at the same distance our own Solar System's gas giants orbit. Here's how they did it.

In our own Solar System, the planets Jupiter and Saturn produce the greatest gravitational influence . [+] on the Sun, which will lead to our parent star moving relative to the Solar System's center-of-mass by a substantial amount over the timescales it takes those giant planets to orbit. This motion results in a periodic redshift and blueshift that should be detectable over long enough observational timescales.

When you look at a star, you're not simply seeing the light it emits from one constant, point-like surface. Instead, there's a lot of physics going on inside that contributes to what you see.

• the star itself isn't a solid surface, but emits the light you see for many layers going down hundreds or even thousands of kilometers,
• the star itself rotates, meaning one side moves towards you and the other away from you,
• the star has planets that move around it, occasionally blocking a portion of its light,
• the orbiting planets also gravitationally tug on the star, causing it to periodically "wobble" in time with the planet orbiting it,

All of these, in some way, matter for detecting planets around a star.

At the photosphere, we can observe the properties, elements, and spectral features present at the . [+] outermost layers of the Sun. The top of the photosphere is about 4400 K, while the bottom, 500 km down, is more like 6000 K. The solar spectrum is a sum of all of these blackbodies, and every star we know of has similar properties to their photospheres.

NASA’s Solar Dynamics Observatory / GSFC

That first point, which might seem the least important, is actually vital to the way we detect and confirm exoplanets. Our Sun, like all stars, is hotter towards the core and cooler towards the limb. At the hottest temperatures, all the atoms inside the star are fully ionized, but as you move to the outer, cooler portions, electrons remain in bound states.

With the energy relentlessly coming from its environment, these electrons can move to different orbitals, absorbing a portion of the star's energy. When they do, they leave a characteristic signature in the star's light spectrum: an absorption feature. When we look at the absorption lines of stars, they can tell us what elements they're made of, what temperature they're emitting at, and how quickly they're moving, both rotationally and with respect to our motion.

The solar spectrum shows a significant number of features, each corresponding to absorption . [+] properties of a unique element in the periodic table or a molecule or ion with electrons bound to it. Absorption features are redshifted or blueshifted if the object moves towards or away from us.

Nigel A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF

The more accurately you can measure the wavelength of a particular absorption feature, the more accurately you can determine the star's velocity relative to your line-of-sight. If the star you're observing moves towards you, that light gets shifted towards shorter wavelengths: a blueshift. Similarly, if the star you're monitoring is moving away from you, that light will be shifted towards longer wavelengths: a redshift.

This is simply the Doppler shift, which occurs for all waves. Whenever there's relative motion between the source and the observer, the waves received will either be stretched towards longer or shorter wavelengths compared to what was emitted. This is true for sound waves when the ice cream truck goes by, and it's equally true for light waves when we observe another star.

A light-emitting object moving relative to an observer will have the light that it emits appear . [+] shifted dependent on the location of an observer. Someone on the left will see the source moving away from it, and hence the light will be redshifted someone to the right of the source will see it blueshifted, or shifted to higher frequencies, as the source moves towards it.

Wikimedia Commons user TxAlien

When the first detection of exoplanets around stars was announced, it came from an extraordinary application of this property of matter and light. If you had an isolated star that moved through space, the wavelength of these absorption lines would only change over long periods of time: as the star we were watching moved relative to our Sun in the galaxy.

But if the star weren't isolated, but rather had planets orbiting it, those planets would cause the star to wobble in its orbit. As the planet moved in an ellipse around the star, the star would similarly move in a (much smaller) ellipse in time with the planet: keeping their mutual center-of-mass in the same place.

The radial velocity (or stellar wobble) method for finding exoplanets relies on measuring the motion . [+] of the parent star, as caused by the gravitational influence of its orbiting planets. Even though the planet itself may not be visible directly, their unmistakable influence on the star leaves a measurable signal behind in the periodic relative redshift and blueshift of the photons coming from it.

In a system with multiple planets, these patterns would simply superimpose themselves atop one another there would be a separate signal for every planet you could identify. The strongest signals would come from the most massive planets, and the fastest signals — from the planets orbiting most closely to their stars — would be the easiest to identify.

These are the properties that the very first exoplanets had: the so-called "hot Jupiters" of the galaxy. They were the easiest to find because, with very large masses, they could change the motion of their stars by hundreds or even thousands of meters-per-second. Similarly, with short periods and close orbital distances, many cycles of sinusoidal motion could be revealed with only a few weeks or months of observations. Massive, inner worlds are the easiest to find.

A composite image of the first exoplanet ever directly imaged (red) and its brown dwarf parent star, . [+] as seen in the infrared. A true star would be much physically larger and higher in mass than the brown dwarf shown here, but the large physical separation, which corresponds to a large angular separation at distances of under a few hundred light years, means that the world's greatest current observatories make imaging like this possible.

European Southern Observatory (ESO)

On the complete opposite end of the spectrum, some planets that are equal to or greater than Jupiter's mass are extremely well-separated from their star: more distant than even Neptune is from the Sun. When you encounter a system such as this, the massive planet is so hot in its core that it can emit more infrared radiation than it reflects from the star it orbits.

With a large enough separation, telescopes like Hubble can resolve both the main star and its large planetary companion. These two locations — the inner solar system and the extreme outer solar system — were the only places where we had found planets up until the explosion of exoplanets brought about by NASA's Kepler spacecraft. Until then, it was only high-mass planets, and only in the places where they aren't found in our own Solar System.

Today, we know of over 4,000 confirmed exoplanets, with more than 2,500 of those found in the Kepler . [+] data. These planets range in size from larger than Jupiter to smaller than Earth. Yet because of the limitations on the size of Kepler and the duration of the mission, the majority of planets are very hot and close to their star, at small angular separations. TESS has the same issue with the first planets it's discovering: they're preferentially hot and in close orbits. Only through dedicated, long-period observations (or direct imaging) will we be able to detect planets with longer period (i.e., multi-year) orbits.

NASA/Ames Research Center/Jessie Dotson and Wendy Stenzel missing Earth-like worlds by E. Siegel

Kepler brought about a revolution because it used an entirely different method: the transit method. When a planet passes in front of its parent star, relative to our line-of-sight, it blocks a tiny portion of the star's light, revealing its presence to us. When the same planet transits its star multiple times, we can learn properties like its radius, orbital period, and the orbital distance from its star.

But this was limited, too. While it was capable of revealing very low-mass planets compared to the earlier (stellar wobble/radial velocity) method, the primary mission only lasted for three years. This meant that any planet that took longer than about a year to orbit its star couldn't be seen by Kepler. Ditto for any planet that didn't happen to block its star's light from our perspective, which you're less likely to get the farther away from the star you look.

The intermediate distance planets, at the distance of Jupiter and beyond, were still elusive.

The planets of the Solar System are difficult to detect using present technology. Inner planets that . [+] are aligned with the observer's line-of-sight must be large and massive enough to produce an observable effect, while outer worlds require long-period monitoring to reveal their presence. Even then, they need enough mass so that the stellar wobble technique is effective enough to reveal them.

Space Telescope Science Institute, Graphics Dept.

That's where a dedicated, long-period study of stars can come in to fill in that gap. A large team of scientists, led by Emily Rickman, conducted an enormous survey using the CORALIE spectrograph at La Silla observatory. They measured the light coming from a large number of stars within about 170 light-years on a nearly continuous basis, beginning in 1998.

By using the same instrument and leaving virtually no long-term gaps in the data, long-term, precise Doppler measurements finally became possible. A total of five brand new planets, one confirmation of a suggested planet, and three updated planets were announced in this latest study, bringing the total number of Jupiter-or-larger planets beyond the Jupiter-Sun distance up to 26. It shows us what we'd always hoped for: that our Solar System isn't so unusual in the Universe it's just difficult to observe and detect planets like the ones we have.

While close-in planets are typically discoverable with stellar wobble or transit method . [+] observations, and extreme outer planets can be found with direct imaging, these in-between worlds require long-period monitoring that's just beginning now. These newly-discovered worlds, down the line, may become excellent candidates for direct imaging as well.

E. L. Rickman et al., A&A accepted (2019), arXiv:1904.01573

Even with these latest results, however, we still aren't sensitive to the worlds we actually have in our Solar System. While the periods of these new worlds range from 15 to 40 years, even the smallest one is nearly three times as massive as Jupiter. Until we develop more sensitive measurement capabilities and make those observations over decadal timescales, real-life Jupiters, Saturns, Uranuses and Neptunes will remain undetected.

Our view of the Universe will always be incomplete, as the techniques we develop will always be inherently biased to favor detections in one type of system. But the irreplaceable asset that will open up more of the Universe to us isn't technique-based at all it's simply an increase in observing time. With longer and more sensitive observations of stars, closely tracking their motions, we can reveal lower-mass planets and worlds at greater distances.

This is true of both the stellar wobble/radial velocity method and also the transit method, which hopefully will reveal even smaller-mass worlds with longer periods. There is still so much to learn about the Universe, but every step we take brings us closer to understanding the ultimate truths about reality. Although we might have worried that our Solar System was in some way unusual, we now know one more way we're not. Having gas giant worlds in the outer solar system may pose a challenge for detections, but those worlds are out there and relatively common. Perhaps, then, so are solar systems like our own.

Mass Loss from Red-Giant Stars and the Formation of Planetary Nebulae

When stars swell up to become red giants, they have very large radii and therefore a low escape velocity. [1] Radiation pressure, stellar pulsations, and violent events like the helium flash can all drive atoms in the outer atmosphere away from the star, and cause it to lose a substantial fraction of its mass into space. Astronomers estimate that by the time a star like the Sun reaches the point of the helium flash, for example, it will have lost as much as 25% of its mass. And it can lose still more mass when it ascends the red-giant branch for the second time. As a result, aging stars are surrounded by one or more expanding shells of gas, each containing as much as 10–20% of the Sun’s mass (or 0.1–0.2 MSun).

When nuclear energy generation in the carbon-oxygen core ceases, the star’s core begins to shrink again and to heat up as it gets more and more compressed. (Remember that this compression will not be halted by another type of fusion in these low-mass stars.) The whole star follows along, shrinking and also becoming very hot—reaching surface temperatures as high as 100,000 K. Such hot stars are very strong sources of stellar winds and ultraviolet radiation, which sweep outward into the shells of material ejected when the star was a red giant. The winds and the ultraviolet radiation heat the shells, ionize them, and set them aglow (just as ultraviolet radiation from hot, young stars produces H II regions see Between the Stars: Gas and Dust in Space).

The result is the creation of some of the most beautiful objects in the cosmos (see the gallery in Figure 3. These objects were given an extremely misleading name when first found in the eighteenth century: planetary nebulae. The name is derived from the fact that a few planetary nebulae, when viewed through a small telescope, have a round shape bearing a superficial resemblance to planets. Actually, they have nothing to do with planets, but once names are put into regular use in astronomy, it is extremely difficult to change them. There are tens of thousands of planetary nebulae in our own Galaxy, although many are hidden from view because their light is absorbed by interstellar dust.

Gallery of Planetary Nebulae.

As Figure 3 shows, sometimes a planetary nebula appears to be a simple ring. Others have faint shells surrounding the bright ring, which is evidence that there were multiple episodes of mass loss when the star was a red giant (see image (d) in Figure 3. In a few cases, we see two lobes of matter flowing in opposite directions. Many astronomers think that a considerable number of planetary nebulae basically consist of the same structure, but that the shape we see depends on the viewing angle (Figure 4). According to this idea, the dying star is surrounded by a very dense, doughnut-shaped disk of gas. (Theorists do not yet have a definite explanation for why the dying star should produce this ring, but many believe that binary stars, which are common, are involved.)

Figure 4. Model to Explain the Different Shapes of Planetary Nebulae: The range of different shapes that we see among planetary nebulae may, in many cases, arise from the same geometric shape, but seen from a variety of viewing directions. The basic shape is a hot central star surrounded by a thick torus (or doughnut-shaped disk) of gas. The star’s wind cannot flow out into space very easily in the direction of the torus, but can escape more freely in the two directions perpendicular to it. If we view the nebula along the direction of the flow (Helix Nebula), it will appear nearly circular (like looking directly down into an empty ice-cream cone). If we look along the equator of the torus, we see both outflows and a very elongated shape (Hubble 5). Current research on planetary nebulae focuses on the reasons for having a torus around the star in the first place. Many astronomers suggest that the basic cause may be that many of the central stars are actually close binary stars, rather than single stars. (credit “Hubble 5”: modification of work by Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA credit “Helix”: modification of work by NASA, ESA, C.R. O’Dell (Vanderbilt University), and M. Meixner, P. McCullough)

As the star continues to lose mass, any less dense gas that leaves the star cannot penetrate the torus, but the gas can flow outward in directions perpendicular to the disk. If we look perpendicular to the direction of outflow, we see the disk and both of the outward flows. If we look “down the barrel” and into the flows, we see a ring. At intermediate angles, we may see wonderfully complex structures. Compare the viewpoints in Figure 4 with the images in Figure 3.

Planetary nebula shells usually expand at speeds of 20–30 km/s, and a typical planetary nebula has a diameter of about 1 light-year. If we assume that the gas shell has expanded at a constant speed, we can calculate that the shells of all the planetary nebulae visible to us were ejected within the past 50,000 years at most. After this amount of time, the shells have expanded so much that they are too thin and tenuous to be seen. That’s a pretty short time that each planetary nebula can be observed (when compared to the whole lifetime of the star). Given the number of such nebulae we nevertheless see, we must conclude that a large fraction of all stars evolve through the planetary nebula phase. Since we saw that low-mass stars are much more common than high-mass stars, this confirms our view of planetary nebulae as sort of “last gasp” of low-mass star evolution.

KELT-9b: Newly-Discovered ‘Hot Jupiter’ Hotter Than Most Stars

Artist’s illustration of the star KELT-9 (left) and its planet KELT-9b (right). The planet takes only 1.5 days to complete a revolution around its host star. Image credit: NASA / JPL-Caltech / Robert Hurt.

KELT-9b is a gas giant 2.8 times more massive than Jupiter but only half as dense.

The planet runs a close orbit to KELT-9, the hottest, most massive and brightest star yet found to host a transiting giant planet.

At approximately 17,850 degrees Fahrenheit (9,900 degrees Celsius, or 10,170 degrees Kelvin), the host star is at the dividing line between stars of type A and B.

Also known as HD 195689, the star is about 650 light-years away in the constellation Cygnus.

Another unique aspect to KELT-9b — the planet orbits the poles of KELT-9 rather than its equator.

“It’s unclear how KELT-9b obtained its peculiar orbit. In addition to being ridiculously close, the planet orbits about the poles of its parent star rather than its equator. One can only imagine how it got there,” said Justin Crepp, Freimann assistant professor of physics at the University of Notre Dame.

Because KELT-9b is tidally locked to KELT-9 — as the Moon is to Earth — the day side of the planet is perpetually bombarded by stellar radiation, and as a result is so hot that molecules such as water, carbon dioxide and methane can’t form there.

With a day-side temperature peaking at 7,820 degrees Fahrenheit (4,327 degrees Celsius, or 4,600 degrees Kelvin), KELT-9b is hotter than most stars.

The properties of the night side are still mysterious — molecules may be able to form there, but probably only temporarily.

Though KELT-9b is larger than Jupiter, it is not as dense. Prof. Crepp and his colleagues believe low surface gravity combined with its extremely high temperature contributes to an inflated and gaseous atmosphere.

UV radiation from KELT-9 is so brutal that the planet may be literally evaporating away under the intense glare, producing a glowing gas tail.

“KELT-9 radiates so much UV radiation that it may completely evaporate the planet,” said Keivan Stassun, professor of physics and astronomy at Vanderbilt University.

“Or, if gas giant planets like KELT-9b possess solid rocky cores as some theories suggest, the planet may be boiled down to a barren rock, like Mercury.”

“That is, if the star doesn’t grow to engulf it first. KELT-9 will swell to become a red giant star in about a billion years,” Prof. Stassun said.

“The long-term prospects for life, or real estate for that matter, on KELT-9b are not looking good.”

A paper reporting this discovery is published in the journal Nature.

B. Scott Gaudi et al. A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host. Nature, published online June 5, 2017 doi: 10.1038/nature22392

The Week That Shook Big Oil

At Chevron's shareholder meeting, investors voted to demand that the company reduce its contribution to climate change. The demand was short on specifics, but investors made it clear that it was not enough to use renewable energy to power oil and gas operations: Real action on climate change means selling less oil.

And a much bigger shareholder revolt took place at Exxon Mobil. Activist investors took on the giant and won, delivering a stinging rebuke to the company's management.

The hedge fund Engine No. 1 placed two new directors on the board of what was once the world's most influential oil company — to prepare it for a world that might stop burning oil and gas.

These events shook the oil industry to its core, upending assumptions about the future of the fuel that powers the global economy.

But this moment has been a long time coming. The scientific consensus that burning oil and gas is driving climate change has been firmly established for decades. For just as long, activists have wielded this scientific evidence in a fight against the world's massive oil and gas giants. They have sued in courts around the world. They have picketed. They have held die-ins.

And they've used the tools of business, arguing that oil and gas is a bad long-term investment.

In a world where governments are determined to tackle climate change, a lot of oil and gas investments might never pay off — they'd become "stranded assets," and companies would lose money.

Activists have presented this financial logic to corporate leaders. They have submitted shareholder proposals. Sometimes they've even won incremental victories.

But they've never had a week like this.

"What's different about this moment is that now we have technologies that are cheaper, cleaner and better, and so the market is recognizing that oil and gas are no longer indispensable," argues Fred Krupp of the Environmental Defense Fund. "The argument that used to be somewhat theoretical about stranded assets is now very tangible and real."

The cost of building new wind and solar power has fallen dramatically. Electric appliances and heat pumps could conceivably replace natural gas in homes. And after Tesla proved that battery-powered vehicles didn't have to be glorified golf carts, the entire auto industry is racing to pivot toward electric vehicles.

Meanwhile, governments around the world — particularly in Europe and China — have been promoting green technology through increasingly aggressive incentives and penalties. Outright climate denial, while still prevalent in countries like the United States, is no longer in the political mainstream.

And more and more investors, including giant, influential money managers like BlackRock, are focusing on climate change. Some groups cite moral reasons, while others focus on the bottom line.

"The biggest risk for us as investors is assuming the status quo and not seeing those risks or those technology disruptions that are around the corner," says Aeisha Mastagni of CalSTRS, the retirement fund for teachers in California. The group was a high-profile backer of the shareholder revolution at Exxon.

"I don't know what the price of oil is going to be tomorrow. I don't know exactly when the world's going to transition," she says. "But I do know that change is coming and Exxon Mobil needs to change with it."

This sense of impending change has reached some oil CEOs and boards of directors.

"Certainly in Europe, there has been a real awakening on the part of a growing number of directors," says Karina Litvack, who serves on the board of directors for the Italian energy company Eni and co-founded the World Economic Forum's Climate Governance Initiative.

"We're certainly not there with everybody, but . directors are aware of the urgency and the complexity and the scale of the climate challenge," she adds.

Increasingly aggressive carbon targets in Europe put pressure on American companies to follow suit meanwhile, as the Dutch court decision against Shell shows, the bar continues to be raised in Europe.

All these forces have converged to create a remarkable moment of reckoning for oil and gas giants.

This week's dramatic news does not suggest that the fight over climate change is over.

In the sometimes-perverse lexicon of corporate America, the idea that the world will wage a successful battle against climate change is a "risk." Specifically, it's called "transition risk."

If the world decides to tackle climate change and transitions away from oil and gas, then a wide array of companies will need to adapt or go under. It may or may not happen, but if it happens, it will carry costs. So from a corporation's point of view, it's a risk.

Exxon Mobil has repeatedly argued that the odds of this happening were so low that it didn't merit planning for it.

Based on the investor revolt this week, Wall Street clearly thinks that a substantial shift away from oil and gas is possible.

Proxy advisory firms, companies that issue recommendations on how investors should vote on shareholder proposals, even used the word "inevitable." And since beliefs about what's possible can shape what's politically viable, this is no small development.

But there's no consensus on when this change would happen.

The oil industry points out that cutting production too early — before the world's demand for oil has actually decreased — would cause price spikes and shortages that would fall somewhere between disruptive and disastrous.

And for demand to drop quickly enough to ward off the worst effects of climate change would require massive investments in renewable power, widespread adoption of electric vehicles, lifestyle changes to cut energy demand, the political will to make disruptive policy changes and international cooperation among rivals and outright enemies.

The world is not currently on track for that kind of transformation.

In short, the fate of the climate is profoundly uncertain. But this week's boardroom and courtroom decisions point to an expanding sense of what's possible.

A massive shift away from fossil fuels is a prospect that Big Oil can no longer rule out.

The Week That Shook Big Oil

At Chevron's shareholder meeting, investors voted to demand that the company reduce its contribution to climate change. The demand was short on specifics, but investors made it clear that it was not enough to use renewable energy to power oil and gas operations: Real action on climate change means selling less oil.

And a much bigger shareholder revolt took place at Exxon Mobil. Activist investors took on the giant and won, delivering a stinging rebuke to the company's management.

The hedge fund Engine No. 1 placed two new directors on the board of what was once the world's most influential oil company — to prepare it for a world that might stop burning oil and gas.

These events shook the oil industry to its core, upending assumptions about the future of the fuel that powers the global economy.

But this moment has been a long time coming. The scientific consensus that burning oil and gas is driving climate change has been firmly established for decades. For just as long, activists have wielded this scientific evidence in a fight against the world's massive oil and gas giants. They have sued in courts around the world. They have picketed. They have held die-ins.

And they've used the tools of business, arguing that oil and gas is a bad long-term investment.

In a world where governments are determined to tackle climate change, a lot of oil and gas investments might never pay off — they'd become "stranded assets," and companies would lose money.

Activists have presented this financial logic to corporate leaders. They have submitted shareholder proposals. Sometimes they've even won incremental victories.

But they've never had a week like this.

"What's different about this moment is that now we have technologies that are cheaper, cleaner and better, and so the market is recognizing that oil and gas are no longer indispensable," argues Fred Krupp of the Environmental Defense Fund. "The argument that used to be somewhat theoretical about stranded assets is now very tangible and real."

The cost of building new wind and solar power has fallen dramatically. Electric appliances and heat pumps could conceivably replace natural gas in homes. And after Tesla proved that battery-powered vehicles didn't have to be glorified golf carts, the entire auto industry is racing to pivot toward electric vehicles.

Meanwhile, governments around the world — particularly in Europe and China — have been promoting green technology through increasingly aggressive incentives and penalties. Outright climate denial, while still prevalent in countries like the United States, is no longer in the political mainstream.

And more and more investors, including giant, influential money managers like BlackRock, are focusing on climate change. Some groups cite moral reasons, while others focus on the bottom line.

"The biggest risk for us as investors is assuming the status quo and not seeing those risks or those technology disruptions that are around the corner," says Aeisha Mastagni of CalSTRS, the retirement fund for teachers in California. The group was a high-profile backer of the shareholder revolution at Exxon.

"I don't know what the price of oil is going to be tomorrow. I don't know exactly when the world's going to transition," she says. "But I do know that change is coming and Exxon Mobil needs to change with it."

This sense of impending change has reached some oil CEOs and boards of directors.

"Certainly in Europe, there has been a real awakening on the part of a growing number of directors," says Karina Litvack, who serves on the board of directors for the Italian energy company Eni and co-founded the World Economic Forum's Climate Governance Initiative.

"We're certainly not there with everybody, but . directors are aware of the urgency and the complexity and the scale of the climate challenge," she adds.

Increasingly aggressive carbon targets in Europe put pressure on American companies to follow suit meanwhile, as the Dutch court decision against Shell shows, the bar continues to be raised in Europe.

All these forces have converged to create a remarkable moment of reckoning for oil and gas giants.

This week's dramatic news does not suggest that the fight over climate change is over.

In the sometimes-perverse lexicon of corporate America, the idea that the world will wage a successful battle against climate change is a "risk." Specifically, it's called "transition risk."

If the world decides to tackle climate change and transitions away from oil and gas, then a wide array of companies will need to adapt or go under. It may or may not happen, but if it happens, it will carry costs. So from a corporation's point of view, it's a risk.

Exxon Mobil has repeatedly argued that the odds of this happening were so low that it didn't merit planning for it.

Based on the investor revolt this week, Wall Street clearly thinks that a substantial shift away from oil and gas is possible.

Proxy advisory firms, companies that issue recommendations on how investors should vote on shareholder proposals, even used the word "inevitable." And since beliefs about what's possible can shape what's politically viable, this is no small development.

But there's no consensus on when this change would happen.

The oil industry points out that cutting production too early — before the world's demand for oil has actually decreased — would cause price spikes and shortages that would fall somewhere between disruptive and disastrous.

And for demand to drop quickly enough to ward off the worst effects of climate change would require massive investments in renewable power, widespread adoption of electric vehicles, lifestyle changes to cut energy demand, the political will to make disruptive policy changes and international cooperation among rivals and outright enemies.

The world is not currently on track for that kind of transformation.

In short, the fate of the climate is profoundly uncertain. But this week's boardroom and courtroom decisions point to an expanding sense of what's possible.

A massive shift away from fossil fuels is a prospect that Big Oil can no longer rule out.

But wait, aliens?!

It seems we left out an important possibility:

• Aliens: A technologically advanced alien civilization might be building something around their star.

Other sources have been reporting that KIC 8462852’s behavior could be evidence of an alien Dyson sphere or an alien megastructure. The researchers didn’t actually discuss this possibility in their paper, where they concluded the comets are currently the best explanation. But as the cometary explanation is not fully satisfying, lead author Tabetha Boyajian of Yale consulted with Jason Wright, an astrophysicist with Penn State University, who had studied ways to detect potential extraterrestrial constructions.

Wright posited that the dips in flux from the star might be due to an alien Dyson sphere. Dyson spheres, of Star Trek fame, are massive, hypothetical constructs built around a star to collect its energy through millions of solar panels.

“Aliens should always be the very last hypothesis you consider,” Wright told The Atlantic. “But this looked like something you would expect an alien civilization to build.”

Well, it does fit the bill. If aliens had built a partial Dyson sphere, it could explain the strange behavior. But that doesn’t mean that’s the correct explanation. As Wright says, it should be the very last hypothesis we consider. And we still have other plausible explanations, such as the comets.

Nonetheless, Wright is writing up a proposal to use the NRAO’s Green Bank Telescope, the world’s largest fully steerable radio telescope, to look for radio transmissions from the system. If accepted, the observation would take place in January. If it turns up something worth further study, it would then be turned over to the Very Large Array in New Mexico, which should be able to confirm if the radio waves come from a technological source.

It’s an interesting idea. While it’s sexier by far than comets, “We should also approach it skeptically,” Wright told Slate. It’s all well and good to investigate the possibility, as Wright is doing, but (despite the impending return of “The X-Files”) it’s not quite time to go "full Mulder" just yet.

If actual evidence exists, we might find out in January. The truth is out there, after all.