September 25, 2022

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Secrets of stars that eat their planets

Secrets of stars that eat their planets

The sun has fed life on earth, but it will not be hospitable forever. Five billion years into the future, the star of our solar system will grow so massive that Mercury, Venus, and possibly Earth will be swallowed whole.

It may seem like a shameful end to our beloved home. But scientists believe that this process of “planet immersion”, in which stars gobble up their planets, is common in the life cycle of stellar systems.

Researchers call them “cannibal stars” (although they are planets that eat them, not other stars), and they may explain mysteries in astronomy, strange orbital formations, and polluted starlight that have baffled scientists for years. But there’s a more basic attraction: Studying planetary swallows may help us understand Earth’s long-term fate and provide clues in the search for extraterrestrial life. What could be more humane than predicting the end of the world and thinking about whether we are alone in the universe?

said Ricardo Yarza, a graduate student in astronomy at the University of California, Santa Cruz, who studies planetary swallows. “It’s always interesting to imagine a civilization that realizes this, like us, and realizes that at some point you have to leave the house.”

Stars come in many varieties including thick dwarfs and hyper-shiny giants. The life expectancy and eventual fate of a star — and therefore any planets orbiting it — is related to its mass: red dwarfs may live for trillions of years, while massive stars explode within a few million.

Sun-sized stars They begin a death ritual when they run out of hydrogen, causing their boundaries to expand hundreds of times. During the “red giant” phase, many stars devour their deep planets before exhausting their remaining fuel.

Red giants, discovered about a century ago, sometimes appear in science fiction stories as ominous backgrounds For doomed civilizations or visions of our solar system the far future. Although we have often imagined the apocalypse creep of advanced stars, the actual process of planetary swallowing remains shrouded in mystery.

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as such As early as 1967For example, astronomers thought about the “ultimate fate of planetary matter” being swallowed up by stars. But they could only speculate, in part because scientists weren’t able to confirm that planets orbited other stars until the 1990s.

since then, Amazing 5000 exoplanets It was detected by missions such as NASA’s Kepler Space Observatory, ushering in a new understanding of the myriad ways in which star systems evolve and how they ultimately die. The next generation of observatories on Earth and beyond, including newly operating observatories James Webb Space Telescopewill depict these worlds in unprecedented detail, shedding light on the possibilities for hosting life.

The sheer abundance of known exoplanets, especially those in narrow orbits, suggests that the lives of many worlds would end within the stomachs of their host stars. But there are many gaps in astronomers’ knowledge because it is difficult to catch stars while devouring planets. Establishing models for engulfing events is also challenging, in part due to the extreme disparity between the sizes of stars and their planetary meals.

said Mr. Yarza, who introduced new search About it before the American Astronomical Society in June. “What happens to planets that swallow?” Do some of them survive? Will they all be destroyed? What happens to the star as a result of ingestion? “

To implement some of these scenarios, Mr. Yarza and colleagues modeled swallowing planets larger than Jupiter in their study, which were Submitted to The Astrophysical Journal. To account for discrepancies in the size of stars and planets, the researchers developed an approach that settled in the star’s gaseous outer region where planets swallow for the first time.

The findings suggest that stars with massive planets can sometimes gnaw on more than they can chew, with serious consequences for both bodies. While Earth-sized worlds devour them without fanfare, planets much larger than Jupiter can take in some stars inside.

Imagine one of these Uber planets where it has finally been overtaken by the fringes of the star that it has imprinted on for billions of years. The gases swirl in vortices where they meet the bodies. As the great scientist descends into hell, he transfers his momentum to the star. The instabilities that arise from this exchange can make the star so out of sight that it ejects its stellar atmosphere into space and subsequently collapses into a dead white dwarf.

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This sequence could explain the “confusing” observations of Planets in close orbits Mr. Yarza said about the white dwarfs. It is unclear how these worlds survived the death of their stars. New models hint at the answer: a sinking giant planet, after stimulating the expulsion of the star’s outer layers, could be pushed into a new, tighter orbit so that it would not be completely burnt up.

It gets even weirder: some giant planets releasing star-killing sparks may also create new worlds into existence as they are amplified in a stellar furnace. “You can have a planet that engulfs, and then it ejects some material, and that material can form a disk around the star forming a new planet,” Mr. Yarza said, describing the new planet as “rising from the ashes.” He added, “You have a planet that gets destroyed, but it does enough in the star that a new planet comes out of it.”

Other outlandish observations include a stellar version of the adage “you are what you eat”: stars become rich in planetary elements like lithium, allowing astronomers to identify cannibal stars by the chemical fingerprints imprinted in their light.

said Melinda Soares Furtado, a NASA postdoctoral fellow at the University of Wisconsin-Madison and co-author of a study book. “But the signatures that are left can be observed for much longer – even billions of years.”

Two-star systems, known as diodes, are ideal environments to look for evidence of sudden ingestion. Double stars are usually born together from the same cloud of gas and dust, which makes them chemically identical. But about 25% to 30% of sun-like stars in binaries have anomalous signals that are “a source of tension between theory and observations,” According to a 2021 study Published in Nature Astronomy.

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Lorenzo Spina, an astrophysicist at the Astronomical Observatory of Padua in Italy and author of that study, believes that these chemical differences could reveal remnants of disembodied worlds. Although it’s unclear how often planets experience this apocalypse – a collision course with a star – it could be a major factor in assessing the potential habitability of other systems.

“We don’t want this situation when we’re looking for a planetary system that could host life,” Dr. Spina said. “We want to find stars that host ‘boring’ planetary systems, let’s say, like our own planetary system, which we know hasn’t changed much in the past.”

On the flip side, dissolutions and mixtures of worlds in stars as they are submerged can open a rare window into the inner components of the outer planets.

“That would be great because the chemical makeup of the planet is really important for life to thrive, of course,” said Dr. Spina.

When thinking about these epic swallows, it’s hard not to wonder if any extraterrestrial civilizations have been unceremoniously thrown into their stars or forced to migrate into the depths of their star systems, moving into newly inhabitable worlds with the warmth of advancing red giants. Within five billion years, the frozen outer worlds of our solar system may be fed by the sun, even when its inner planets are consumed.

Dr. Soares Furtado said ingestion is “the fate of Mercury and Venus in our solar system, if you speed up the clock and look at what happens to the sun.” “You have Jupiter, Saturn, and Uranus all sitting in a nice habitable zone” all at once, she added.

With the new telescopes, she said, scientists will get “more glimpses of those later stages.”