A rare glimpse of a star before it went supernova defies expectations

An uncommon glimpse of a star earlier than it exploded in a fiery supernova seems to be nothing like astronomers anticipated, brand new research suggests.

Images from the Hubble Space Telescope reveal {that a} comparatively cool, puffy star ended its life in a hydrogen-free supernova. Until now, supernovas without hydrogen had been thought to originate solely from extraordinarily sizzling, compact stars.

The discovery “is a very important test case for stellar evolution,” says Sung-Chul Yoon, an astrophysicist at Seoul National University in South Korea, who was not concerned within the work. Theorists have some concepts about how huge stars behave properly earlier than they blow up, however, such hefty stars are scant within the native universe and lots of are nowhere close to able to go supernova, Yoon says. Retroactively figuring out the star accountable for a supernova offers a chance to check eventualities of how stars evolve properly earlier than exploding.

Finding these stars, nevertheless, is troublesome, explains Charlie Kilpatrick, an astronomer at Northwestern University in Evanston, Ill. A telescope will need to have checked out that actual area of the sky within the years main as much as the supernova. And the explosion will need to have occurred shut sufficient for mild from its a lot fainter supply star to have reached a telescope.

Although each situation is difficult to fulfill, Kilpatrick is undaunted by the hunt. After scientists found a supernova in December 2019, in a galaxy referred to as NGC 4666 about 46 million light-years away, he and colleagues rushed to test previous Hubble observations from the identical area of the sky. They needed to seek out the star behind the explosion, dubbed SN 2019yvr.

After pouring over photographs and cross-checking observations with these from ground-based telescopes, the crew discovered their quarry: a star on the identical spot because the supernova noticed about 2.6 years earlier than the explosion. It seemed to be a yellow star about 6,500° Celsius and about 320 occasions wider than the solar.

“I was kind of puzzled by all that,” Kilpatrick says. The supernova SN 2019yvr lacked hydrogen, so its progenitor was anticipated to be hydrogen-deficient, too. But “if a star lacks a hydrogen envelope, then you expect to be seeing the deeper inside of the star to the hotter layers,” Kilpatrick says. That is, the star ought to have appeared extraordinarily sizzling and blue and compact — possibly 10,0000 to 50,000° C, and no more than 50 occasions wider than the solar. The cool, massive, yellow progenitor of SN 2019yvr, then again, appeared to be padded with lots of hydrogen. The researchers report the outcomes on May 5 within the Monthly Notices of the Royal Astronomical Society.

For this sort of star to have produced a supernova like SN 2019yvr, it will need to have shed a lot of its hydrogen earlier than blowing up, Kilpatrick says. But how?

He and colleagues have given you a pair of eventualities. The star may have expelled a lot of its hydrogen into the house via violent eruptions, presumably attributable to some instability within the star’s core or interference from one other star close by. Or maybe the star’s hydrogen may have been stripped off by one other star that was in orbit around it.

To whittle these potentialities down, Jan Eldridge, an astrophysicist at the University of Auckland in New Zealand, suggests turning the Hubble telescope again on that space of the sky. Astronomers ought to first ensure that the star was seen 2.6 years earlier than SN 2019yvr actually is gone now, says Eldridge, who was not concerned within the work. Researchers may additionally test whether or not a star that when orbited SN 2019yvr’s progenitor nonetheless stays.

“They’ve found a mystery, and they’ve got some solutions,” Eldridge notes. Trying to determine how such an unlikely star pulled off this specific supernova, she says, “is going to be fun.”