Astronomers witness the explosive death of a giant star for first time

For the first time, astronomers have observed the last days and death throes of a red giant star before its final collapse and massive explosion into a supernova.

Supernovas are usually only detected after they occur, although a few different types were discovered during the explosion process. In this case, the scientists discovered the star in its final stages about 130 days before it exploded, and were able to watch it grow gradually, and then finally explode.

“It’s like watching a time bomb,” astrophysicist Raffaella Margotti, senior author of a study on the supernova published last week in The Astrophysical Journal, said in a statement. “We’ve never been certain of such violent activity in a dying red giant star that we see it produce such a luminous emission, then collapse and ignite, until now.”

Margotti is now an associate professor of astronomy and physics at the University of California, Berkeley, but she conducted the study while working at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). In Evanston, Illinois.

The lead author of the new study is Margotti’s graduate student, astrophysicist Wayne Jacobson-Gallan, who was also at Northwestern for observations but has since joined UC Berkeley.

The star was discovered in the summer of 2020 during a survey conducted by the University of Hawaii’s Pan-STARRS telescope on top of the Haleakala volcano on Maui, Jacobson Gallan said.

Although the star was in a galaxy about 120 million light-years away – both the star and the galaxy are very faint To see it with the naked eye – data from Pan-STARRS showed that the star became much brighter than usual, he said.

Then the scientists observed the star with the Pan-STARRS telescope, which showed that it violently ejected large amounts of gas.

When the last supernova explosion occurred, they were able to capture the powerful flash it emitted – for a brief moment, it was brighter than all the other stars in that galaxy combined – thanks to CIERA’s ability to operate remote telescopes at the WM Keck Observatory atop Mauna Kea in Hawaii.

The supernova flash and subsequent observations showed that the star was surrounded by shells of gas when it exploded – likely the same gas it released in the month before the explosion.

A few other supernovae have been seen before, but not of this type. Jacobson Gallan said they were usually when a giant star collided with his duo.

But in this case, it appears that no other stars were involved in the explosion.

“These types of supernovae come from a massive star and usually a red giant,” he said. “And that’s what we saw – they’re one of the most common supernovae in the universe.”

Observations after the explosion indicated that the star was about 10 times larger than our sun – near the lower end of the star’s range that became a supernova.

Stars like our sun are too small to be supernovas. They will expand and then shrink into a white dwarf at the end of their lives.

Smaller stars also last for several billion years, Jacobson Gallan said, because they are not so large that they burn all their fusion fuel in a short time.

However, the red giants like the supernova in the study can only use up their fuel in a few hundred million years, and then collapse when they can’t do fusion anymore.

The latest supernova is caused by the “bounce” of the star’s outer shells from its core.

“This spreads outward and takes apart the whole star,” he said. “It’s ripping through the star and pushing all the layers out really fast.”

Supernovas are the final stages of many stars, and are responsible for seeding interstellar clouds of gas and dust with “heavy” chemical elements. The clouds from the eruptions then coalesce to form younger stars, like the Sun, and the elements — such as carbon, oxygen, silicon, and iron — are fused into their planets.

Previously, it was nearly impossible to observe the “aging” of massive stars, said Matt Nicholl, a lecturer in physics and astronomy at the University of Birmingham in the UK. “Before now, we’d never been able to directly study this crucial stage,” he said in an email.

Nicole was not involved in the latest study, but he led a team that discovered the brightest supernova ever.

He said that dedicated robotic telescopes such as Pan-STARRS can now scan the sky for explosive events such as supernovae, and more are likely to be found as the surveys become more effective.

Although Jacobson Gallan suggests that the star’s brightness before it became a supernova was a result of its final stages, Albert Zelstra, professor of astrophysics at the University of Manchester in the UK, said in an email that the brightness may have been. Not connected.

Zijlstra was not involved in the new study but is an expert on supernovae. He was part of a team that identified the star that exploded to create the supernova seen over China in AD 1181.

He points to a similar star, Eta Carinae, about 7,500 light-years away, which emits vast clouds of gas and gets brighter for many years at a time, but fades again without exploding.

“They saw a bright flash before the explosion, but there’s no way of knowing that the star didn’t do the same thing 10 years ago,” Zijlstra said. “So we don’t know if the two things are related or not.”

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