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In about 5 billion years, Earth.
Astronomers Witness a Star Devouring a Planet – “We Are Seeing the Future of the Earth”
As a star runs out of fuel, it will billow out to a million times its original size, engulfing any matter — and planets — in its wake. Scientists have observed hints of stars just before, and shortly after, the act of consuming entire planets, but they have never caught one in the act until now.
In a study that will appear in Nature, scientists at MIT, Harvard University, Caltech, and elsewhere report that they have observed a star swallowing a planet, for the first time.
The planetary demise appears to have taken place in our own galaxy, some 12,000 light-years away, near the eagle-like constellation Aquila. There, astronomers spotted an outburst from a star that became more than 100 times brighter over just 10 days, before quickly fading away. Curiously, this white-hot flash was followed by a colder, longer-lasting signal. This combination, the scientists deduced, could only have been produced by one event: a star engulfing a nearby planet.
“We were seeing the end-stage of the swallowing,” says lead author Kishalay De, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research.
What of the planet that perished? The scientists estimate that it was likely a hot, Jupiter-sized world that spiraled close, then was pulled into the dying star’s atmosphere, and, finally, into its core.
A similar fate will befall the Earth, though not for another 5 billion years, when the sun is expected to burn out, and burn up the solar system’s inner planets.
“We are seeing the future of the Earth,” De says. “If some other civilization was observing us from 10,000 light-years away while the sun was engulfing the Earth, they would see the sun suddenly brighten as it ejects some material, then form dust around it, before settling back to what it was.”
The study’s MIT co-authors include Deepto Chakrabarty, Anna-Christina Eilers, Erin Kara, Robert Simcoe, Richard Teague, and Andrew Vanderburg, along with colleagues from Caltech, the Harvard and Smithsonian Center for Astrophysics, and multiple other institutions.
The team discovered the outburst in May 2020. But it took another year for the astronomers to piece together an explanation for what the outburst could be.
The initial signal showed up in a search of data taken by the Zwicky Transient Facility (ZTF), run at Caltech’s Palomar Observatory in California. The ZTF is a survey that scans the sky for stars that rapidly change in brightness, the pattern of which could be signatures of supernovae, gamma-ray bursts, and other stellar phenomena.
De was looking through ZTF data for signs of eruptions in stellar binaries — systems in which two stars orbit each other, with one pulling mass from the other every so often and brightening briefly as a result.
“One night, I noticed a star that brightened by a factor of 100 over the course of a week, out of nowhere,” De recalls. “It was unlike any stellar outburst I had seen in my life.”
