Scientists have observed a Sun-like star gobble up a planet for the first time, confirming predictions that Earth will meet the same fate in 5 billion years.
Scientists at MIT, along with Harvard University and Caltech, have observed some hints of stars just before and shortly after an event that consumes entire planets, but they haven’t caught an event yet.
Published in the journal Nature, the planetary extinction appears to have occurred in our own galaxy, about 12,000 light-years away, near the Eagle Cluster. Astronomers have discovered an explosion from a star that grew 100 times brighter in 10 days before quickly disappearing. This white-hot flash was strangely followed by a cooler, longer-duration signal. Scientists have calculated that this combination could be the result of a single event: a star engulfing a nearby planet.
„We looked at the final stages of the engulfment,” said lead author Kishale Di, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research.
Scientists estimate that it may have been a hot, Jupiter-sized world that orbited close to, then was pulled into, the dying star’s atmosphere and, finally, at its core.
A similar fate will befall Earth, although the Sun is expected to burn up and burn up the inner planets of the Solar System for another 5 billion years.
„We’re looking at the future of Earth,” Dee said.
„If some other civilization were watching the Americas from 10,000 light-years away as the Sun engulfed the Earth, they would see the Sun suddenly brighten, eject some material, dust around it, and return to where it was.” D added.
The study’s MIT co-authors include Diepto Sagraparti, Anna-Christina Eilers, Erin Cara, Robert Simcoe, Richard Deek, and Andrew Vanderburgh, as well as colleagues at Caltech, Harvard, and the Smithsonian Center for Astrophysics, among others.
Hot and cold
Researchers discovered the eruption in May 2020. But it took another year for astronomers to piece together an explanation for what the explosion might have been.
A search of data taken by the Zwicky Transient Facility (ZTF) at Caltech’s Palomar Laboratory in California showed the initial signal. The ZTF is a survey that scans the sky looking for stars that change rapidly in brightness, which can be signatures of supernovae, gamma-ray bursts, and other stellar events.
De was looking at the ZTF data for signs of explosions in galactic binaries — two stars orbiting each other, one frequently pulling mass from the other and resulting in brief flashes.
„One night, out of nowhere, I noticed a star that had brightened by a factor of 100 in a week,” Dee recalled.
„It was unlike any starburst I’ve ever seen in my life,” Di added.
Hoping to pinpoint the source with more data, he looked at observations of the same star taken by the Keck Observatory in Hawaii. Keck telescopes take spectroscopic measurements of starlight, which scientists can use to determine a star’s chemical composition.
But what D found confused him even more. Most binaries produce interstellar material such as hydrogen and helium when one star corrodes another, yielding nothing new. Instead, Dee saw signs of „strange molecules” that exist only at very cold temperatures.
„These molecules are only found in stars that are very cool,” Dee said.
„When a star gets brighter, it usually gets hotter. So, low temperatures and bright stars don’t go together,” Di added.
A happy coincidence
It was then clear that the signal was not a stellar binary. I decided to wait for more answers to come out. About a year after his initial discovery, he and his colleagues analyzed observations of the same star, this time taken with an infrared camera at the Palomar Observatory. In the infrared band, astronomers can see signals from cooler objects, in contrast to the white-hot, optical emissions that arise from binaries and other extreme stellar events.
„That infrared data made me fall off my chair,” Dee said.
„The near-infrared source was very bright,” Di added.
After its initial hot flash, the star seemed to continue to blow cool energy over the next year. That cooler material may be gas from the star that has been ejected into space and condensed into dust, cool enough to be detected at infrared wavelengths. These data suggested that the star may have merged with another star rather than become brighter as a result of a supernova explosion.
But when the team analyzed the data further and combined it with measurements taken by NEOWISE, NASA’s infrared space telescope, they came to a more surprising realization. From the compiled data, they estimated the total amount of energy released from the star’s initial explosion, and found it to be surprisingly small — about 1/1,000 the size of any stellar merger observed in the past.
„That means everything connected to the star must be 1,000 times smaller than any other star we’ve seen,” Dee says. „It was a happy coincidence that Jupiter’s mass was 1/1,000 the mass of the Sun. That’s when we realized: It’s a planet that’s crashed into its star.”
With the fragments in place, scientists were finally able to explain the initial explosion. The bright, hot flash could be the final moments of a Jupiter-sized planet being pulled into the ballooning atmosphere of a dying star. As the planet fell into the star’s core, the star’s outer layers exploded and settled into cold dust over the next year.
„For decades, we’ve been able to see back and forth,” Dee says. „Earlier, when planets are still orbiting very close to their star, and later, when a planet is already submerged, and the star is giant, what we’re missing is that you have to capture a planet in action. This rule in real time. That’s what makes this discovery so exciting.”
This research was supported in part by NASA, the US National Science Foundation, and the Heising-Simons Foundation.