Astronomers have known the fate of planets like Mercury, Venus, and Earth when their host stars are about to die, but never have they observed it happening in space — until now.
Using the Gemini South telescope in Chile, scientists have seen the first evidence of a bloated old star absorbing an exoplanet as it puffs out during its final death throes. The event was observed in a long, low-energy outburst — the sign of a planet skimming a star's surface.
In the past, astronomers have found evidence of stars that have consumed planets, sometimes by doing a sort of post-mortem autopsy on what's left of the dead star. But new research published in the journal Nature presents the first direct evidence of star-eats-planet as it happened. The group hopes the event will provide other researchers with helpful clues to discover other stars consuming planets elsewhere in the universe.
"Our interpretation...provides evidence for a missing link in our understanding of the evolution and final fates of planetary systems," the study's authors wrote.
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During the event approximately 12,000 light-years away from Earth in the direction of the constellation Aquila, the dying star, about the size of the sun, absorbed a planet up to ten times the mass of Jupiter, according to the study.
"Our interpretation … provides evidence for a missing link in our understanding of the evolution and final fates of planetary systems."
Unlike giant stars that explode into a supernova and collapse into a black hole, a medium star like the sun suffers a more tortured end by dying slowly. A so-called "planetary nebula" — a confusing misnomer because stars cause them, not planets — is a phenomenon made from the molted layers of an elderly star. Such spectacular clouds of gas and dust occur when a star withers away as it loses nuclear fuel.
What remains of the star's core grows cold. Then, the light goes out.
Do stars eat planets?
"For decades, we’ve been able to see the before and after," said Kishalay De, an MIT researcher and the lead author, in a university news release. "Before, when the planets are still orbiting very close to their star, and after, when a planet has already been engulfed, and the star is giant. What we were missing was catching the star in the act, where you have a planet undergoing this fate in real-time. That’s what makes this discovery really exciting."
Astronomers expect this is the future of the sun in about 5 billion years.
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It would be impossible to watch a single star go through its entire lifecycle for obvious reasons: That would take billions of years, said Paul Sutter, a professor at Stony Brook University and author of How to Die in Space, in an interview with Mashable last year. But experts have been able to predict such a grotesque end for a planet by studying many stars at different intervals and how they interact with their surroundings as they age.
"It's like taking a snapshot of everyone on the Earth in one moment. You can't capture one person's lifetime, but you can see people being born, you can see people playing soccer in elementary school, and you can see people getting married. You can see people dying, getting sick," said Sutter, who wasn't involved in the new study. "You can reconstruct the life cycle of a person by putting together all these separate pieces, so we have a general picture of how stars evolve and how they live."
Will the sun eat Earth?
Evidence suggests that as the sun eventually goes through this slow demise, Earth will likely face the same destiny as the planet observed by the research group.
"We're not exactly sure how big the sun will get — there is a little bit of uncertainty, in that either it will completely engulf the Earth or it will merely come up to basically the edge of our orbit," Sutter said previously. "It would incinerate the Earth anyway."
The new study confirms that when a sun-like star nears the end of its life, it expands into a red giant, 100 to 1,000 times its original size, eventually overtaking nearby planets. Such events are thought to be rare, occurring only a few times each year throughout the galaxy.
The outburst caused by the star engulfing the planet lasted about 100 days, according to the study.
"I think there's something pretty remarkable about these results that speaks to the transience of our existence," said Ryan Lau, a NOIRLab astronomer and co-author, in a statement. "After the billions of years that span the lifetime of our Solar System, our own end stages will likely conclude in a final flash that lasts only a few months."
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