A curiously yellow star has caused astrophysicists to re-evaluate what is possible in our universe.
Led by Northwestern University, the international team used NASA’s Hubble Space Telescope to examine the massive star two and a half years before it exploded into a supernova. At the end of their life, cold yellow stars are usually shrouded in hydrogen, which conceals the star’s warm blue interior. But this yellow star, located 35 million light-years from Earth in the Virgo cluster of galaxies, mysteriously lacked that crucial layer of hydrogen when it exploded.
“We’ve never seen this scenario before,” said Charles Kilpatrick of Northwestern, who led the study. “If a star explodes without hydrogen, it should be extremely blue – really, really hot. It is almost impossible for a star to be this cold without having hydrogen in its outer shell. like that, and every model requires the star to have hydrogen, which from its supernova we know it doesn’t. It expands what is physically possible. “
The team describes the particular star and its resulting supernova in a new study, which was published today (May 5) in the Monthly notices from the Royal Astronomical Society. In the article, the researchers hypothesize that in the years leading up to its death, the star could have shed its hydrogen layer or lost it to a nearby companion star.
Kilpatrick is a postdoctoral fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern and a member of the Young Supernova Experiment, which uses the Pan-STARSS telescope in Haleakal ?, Hawaii, to catch supernovae just after they explode.
Catch a star before it explodes
After the Young Supernova experiment spotted the 2019yvr supernova in the relatively nearby spiral galaxy NGC 4666, the team used deep space images captured by NASA’s Hubble Space Telescope, which luckily observed this section already. of the sky.
“What massive stars do just before they explode is a great unsolved mystery,” Kilpatrick said. “It’s rare to see this kind of star just before it explodes into a supernova.”
Hubble images showed the source of the supernova, a massive star photographed just years before the explosion. While the supernova itself looked quite normal, its source – or progenitor star – was anything but.
“When it exploded, it looked like a very normal hydrogen-free supernova,” Kilpatrick said. “There was nothing exceptional about it. But the progenitor star did not correspond to what we know about this type of supernova.”
Direct evidence of violent death
Several months after the explosion, however, Kilpatrick and his team discovered a clue. When the ejecta from the star’s final explosion passed through its surroundings, they collided with a large mass of hydrogen. This led the team to hypothesize that the progenitor star could have expelled hydrogen a few years before its death.
“Astronomers suspected that the stars would undergo violent eruptions or death pangs in the years before we saw supernovae,” Kilpatrick said. “The discovery of this star provides some of the most direct evidence ever found that stars undergo catastrophic eruptions, which cause them to lose mass before an explosion. If the star had these eruptions, then it likely expelled its hydrogen several times. decades before exploding. “
In the new study, Kilpatrick’s team also presents another possibility: a less massive companion star could have removed hydrogen from the supernova’s progenitor star. The team, however, will not be able to search for the companion star until the supernova’s luminosity has dimmed, which could take up to 10 years.
“Contrary to its normal behavior right after it exploded, the hydrogen interaction revealed it to be some sort of bizarre supernova,” Kilpatrick said. “But it’s amazing that we were able to find its parent star in the Hubble data. In four or five years, I think we can find out more about what happened.”