- Astronomers discovered a distant star swallowing a planet for the first time ever.
- It’s a glimpse of the future: In 5 billion years, the sun will swell to engulf Earth.
- This star gulped a Jupiter-sized planet and left only dust. Earth’s death will be even less dramatic.
A distant, Jupiter-sized planet found itself in serious trouble when its star began to die — the same fate Earth will eventually face.
As the alien star burned through the last of its hydrogen fuel, it swelled to 100 times its original size, its atmosphere ballooning outward toward the orbiting planet. That world, meanwhile, was spiraling closer and closer to the swollen star with each orbit.
Finally, the dying star’s atmosphere engulfed the planet, then pulled it into its core. Swallowing the planet whole produced a burst of energy that expelled the star’s outer layers, causing it to expand and brighten rapidly.
The gas from the star’s ejected layers then cooled and condensed into a cloud of dust — the only remaining evidence that a planet was ever there.
That’s what astronomers have determined after watching the star, 12,000 light-years away, suddenly burst with white-hot light, growing 100 times brighter in just 10 days, before quickly fading and turning cold.
This is exactly how Earth will die. In about 5 billion years, when the sun burns out and swells, it will devour all the inner planets: Mercury, Venus, and Earth.
“We are seeing the future of the Earth,” Kishalay De, a postdoctoral fellow at MIT’s Kavli Institute for Astrophysics and Space Research, who led the discovery, said in a press release. “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.”
De and his colleagues at Harvard University, Caltech, and other institutions published their findings in the journal Nature on Wednesday.
Swallowing Earth will be a ‘minor’ feat for the sun
Scientists think that most planets will die this way. This is the first time they’ve seen it happen live, thanks to lucky timing and the sheer size of the planet.
Even for that giant world, though, it was “almost like the star ate that planet and forgot about it completely,” De said in a briefing with journalists on Tuesday.
Except for a veneer of dust, the star pretty much looked the same as it had before, one year after devouring its planet.
For the sun, swallowing Earth will be even more insignificant. The distant planet that just got absorbed by its star was about the size of Jupiter, which is more than 1,300 Earths.
By comparison, Mercury, Venus, and Earth will probably be “really minor perturbations to the power output of the sun,” Morgan MacLeod, a postdoc at the Harvard-Smithsonian Center for Astrophysics, and a co-author of the new study, said in the briefing.
“When the sun evolves and swallows the solar system planets, it might not really disturb that future sun at all,” he said.
Luckily, humans — and probably all other life forms — won’t be around to see that. At that point, Earth will have been inhospitable for tens of thousands of years. As the sun swells toward it, all the planet’s water will likely evaporate and it will become too hot for life as we know it.
Three clues pointed to the first glimpse of a star absorbing a planet
De first spotted the dying star while he was looking for novae — stars that devour so much gas from a neighboring star that it causes a nuclear explosion, erupting thousands of times brighter in a period of just weeks.
For any potential nova he spotted, he looked again with the Keck Observatory in Hawaii, which breaks down the wavelengths of light emitting from the star, to determine its chemical composition.
That’s when he began to scratch his head about this one star 12,000 light-years away. It was full of molecules that can only exist at very cold temperatures. That was the first clue that something was unusual about this star.
“That’s when we realized that it was nothing like a nova at all,” De said.
A nova should be surrounded by hot gas. This star was sitting in cold gas — which would be bright in infrared light. So De and his colleagues pointed an infrared camera at the star.
There was clue number two: It was blindingly bright in infrared, suggesting the star was surrounded in dust. It must have ejected that dust as part of the bright outburst that first drew De’s attention.
How long had the dust been there? NASA’s infrared space telescope, NEOWISE, would have a record of it. So De went back through its data.
That’s where they found the third clue: Dust had been clouding around the star for months before its bright outburst. This was definitely not a star eating another star. (It later turned out, this pre-eruption dust was material from the planet skimming the atmosphere of the star as it orbited closer and closer.)
They calculated the total energy output from all this dust and expelled gas from the star, and determined that the object the star was eating must be about 1,000 times smaller than a star — about the size of a planet.
“Since we’ve known that there are planets around other stars, it’s been almost an inevitable prediction that stars must engulf their planets as they evolve,” De said. “What we’ve never really seen before is the impact of the engulfment itself. And that was the missing piece in this entire puzzle.”