Galactic gobble: Star swallows planet in one big gulp
Using a Maunakea telescope, scientists have, for the first time, caught a star in the act of swallowing a planet.
Astronomers on Wednesday reported their observations of what appeared to be a gas giant around the size of Jupiter or bigger being eaten by its star. The sun-like star had been puffing up with old age for eons and finally got so big that it engulfed the close-orbiting planet.
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It’s a gloomy preview of what will happen to Earth when our sun morphs into a red giant and gobbles the four inner planets.
“Something like this will happen to our solar system in about four to five billion years,” said Viraj Karambelkar, a grad student at the California Institute of Technology, and co-author of the study.
This galactic feast happened between 10,000 and 15,000 years ago near the Aquila constellation when the star was around 10 billion years old. As the planet went down the stellar hatch, there was a swift hot outburst of light, followed by a long-lasting stream of dust shining brightly in cold infrared energy, the researchers said.
Massachusetts Institute of Technology researcher Kishalay De spotted the luminous outburst in 2020 while reviewing sky scans taken by the California Institute of Technology’s Palomar Observatory. Those scans initially appeared to be a nova explosion, caused by a white dwarf star stealing matter from a companion star.
“But this seemed to come out of nowhere,” Karambelkar said, explaining that De had been specifically searching for binary star interactions, but had come across a similar-looking phenomenon occurring with a solitary star.
But additional observations using the W. M. Keck Observatory atop Maunakea revealed the truth: Instead of a star gobbling up its companion star, this one had devoured its planet.
An instrument at Keck, the Low Resolution Imaging Spectrometer, confirmed that the outburst had a different chemical composition and a cooler temperature than an interaction between two stars would have.
“If it was two stars, it should have been expelling hydrogen and helium, but this had a lot of weird molecules and cooler temperatures,” Karambelkar said.
While there had been previous signs of other stars nibbling at planets and their digestive aftermath, this was the first time the swallow itself was observed, according to the study appearing in the journal Nature.
Given a star’s lifetime of billions of years, the swallow itself was quite brief — Karambelkar said the process of the planet falling into the star likely took just a matter of days.
The findings are “very plausible,” said Carole Haswell, an astrophysicist at Britain’s Open University, who had no role in the research. Haswell led a team in 2010 that used the Hubble Space Telescope to identify the star WASP-12 in the process of eating its planet.
“This is a different sort of eating. This star gobbled a whole planet in one gulp,” Haswell said in an email. “In contrast, WASP-12 b and the other hot Jupiters we have previously studied are being delicately licked and nibbled.”
Astronomers don’t know if more planets are circling this star at a safer distance. If so, De said they may have thousands of years before becoming the star’s second or third course.
Now that they know what to look for, the researchers will be on the lookout for more cosmic gulps.
“Things like this shouldn’t be very rare,” Karambelkar said. “Based on what we know, like the sun should be doing this all the time.”
And eventually, our sun will do the same to Earth.
“All that we see around us, all the stuff that we’ve built around us, this will all be gone in a flash,” De said.
