Astronomers have been watching the end of the world for thousands of years. Sky watchers noted the rare star suddenly bursting into light and then fading away over time. The stellar deaths can also destroy a star's planets. Black holes shredding entire stars and finding evidence for debris from shattered rocky worlds raining down on white dwarf stars are some of the things modern researchers can see.
There are only hints at a planet's death throes. The results of a new preprint study show the way to more direct observations of annihilation, forecasting the types of worlds that can be engulfed by their stars and the resulting boost in stellar brightness that ensues. Astronomers will be able to see the telltale flaring produced during a planet's final moments as it is devoured by its star. They may be able to find some that survive the plunge.
Yarza is a graduate student at the University of California, Santa Cruz. It is not comprehended in detail. Yarza and his colleagues modeled the interaction between planets and red giants.
Their results suggest that the largest planets, at least 10 times the size of Jupiter, can survive by blowing off their star's outer layers. A brief stellar flickering can be caused by smaller worlds. They should not get away from a hungry star. The research was presented at the American Astronomical Society meeting.
Our own sun is expected to become one five billion years from now, when it will be a red giant. When a star runs out of hydrogen fuel at its core and begins burning helium instead, it causes the star to swell to 100 times its previous size. The star can encompass any worlds that are close to it. Mercury and Venus will experience this. The star expels its outer layers, too, as it puffs up. Some planets can be avoided by drifting outward. In this way, the earth may eventually escape. Raising tides on the star that can suck away the tugging planet's momentum causes the world to spiral in to its potential doom. Not every planet is destined for disaster.
Whether a world succumbs or lasts depends on how it interacts with the red giant after it has been engulfed. A planet can sink into the stellar core, where it will be completely shredded, because of the tempestuous atmosphere inside a star. It slows the planet's descent and dumps energy into the gas when it passes through the stellar atmosphere. The star's outermost layer can expand and billow away if a planet stirs up the gas at the star's outskirts.
The graduate student who was not part of the new study says that if it can blow away the layers before it reaches the point of no return, it will survive.
To survive a planet needs to be precisely timed. The dense atmosphere of the star will be more resistant to being thrown away if that entry is too early. The star's outer layers become more diffuse as it sheds material. A planet entering a star later in the red giant phase is more likely to survive because it can peel away the star's outer layers.
The planet can be engulfed by the star for a long time. Yarza says that the more time the planet spends inside the star the longer it will be affected by drag forces. Exposure to atmospheric drag slows the planet's journey and gives it more time to blow off the stellar envelope. Only the largest planets are large enough to benefit.
Even though a planet can be swallowed, it can still leave traces of its fate.
Astronomers have noticed for a long time that some giant stars are rotating more quickly than expected. The souped-up stellar spins are probably caused by planets.
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Smadar Naoz, a researcher at the University of California, Los Angeles, was not a part of the study. As many as 40 percent of the fast-rotating stars in open clusters are consistent with having eaten planets, according to Naoz.
Red giants have recently eaten worlds in their outer layers. Yarza says that a small percentage of red giants are rich in the mineral. He says that it's strange because it's easy to burn in stars. A doomed planet falling into a star can be explained by a model. Pieces of the destroyed world can be seen if the stellar material welling up from beneath is visible.
Studies have shown that stars eating their planets can briefly light up. Yarza and his colleagues refined their earlier predictions by calculating how the energy of an engulfed planet is transferred into a star. Yarza says that even a Jupiter-sized planet can cause a blip in the sky.
Eva Villaver is a professor at Spain's Center for Astrobiology who studies how stars interact with their environments.
A researcher at the Rochester Institute of Technology who was not a part of the study said that the brightening effect should be visible with current instruments. If you have a decade of images, you can start looking for things that match the increased luminosity.
It is hard to catch a star at this time. We might get lucky. Astronomers believe that most stars are accompanied by at least one planet, based on extrapolations from surveys and the thousands of exoplanets now known. It seems that telescopes will show some red giants in unexpected ways, and with them, the gruesome fates of swallowed worlds.
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