A uncommon glimpse of a star earlier than it went supernova defies expectations

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

Photographs from the Hubble House Telescope reveal {that a} comparatively cool, puffy star ended its life in a hydrogen-free supernova. Till now, supernovas with out hydrogen have been thought to originate solely from extraordinarily scorching, compact stars.

The invention “is an important check case for stellar evolution,” says Sung-Chul Yoon, an astrophysicist at Seoul Nationwide College in South Korea, who was not concerned within the work. Theorists have some concepts about how huge stars behave proper 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 answerable for a supernova offers a possibility to check eventualities of how stars evolve proper earlier than exploding.

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

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

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

“I used to be type of puzzled by all that,” Kilpatrick says. The supernova SN 2019yvr lacked hydrogen, so its progenitor was anticipated to be hydrogen-deficient, too. However “if a star lacks a hydrogen envelope, you then anticipate to be seeing deeper inside the star to the warmer layers,” Kilpatrick says. That’s, the star ought to have appeared extraordinarily scorching and blue and compact — possibly 10,0000 to 50,000° C, and not more than 50 occasions wider than the solar. The cool, massive, yellow progenitor of SN 2019yvr, alternatively, gave the impression to be padded with a lot of hydrogen. The researchers report the outcomes Could 5 within the Month-to-month Notices of the Royal Astronomical Society.

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

He and colleagues have give you a pair eventualities. The star might have expelled a lot of its hydrogen into house by way of violent eruptions, presumably brought on by some instability within the star’s core or interference from one other star close by. Or maybe the star’s hydrogen might have been stripped off by one other star that was in orbit round it.

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

“They’ve discovered a thriller, and so they’ve acquired some options,” Eldridge notes. Attempting to determine how such an unlikely star pulled off this specific supernova, she says, “goes to be enjoyable.”

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