The star that survived a supernova

Galaxy NGC 1309. Credit: NASA, ESA, The Hubble Heritage Team (STSCI/AURA) and A. Riess (JHU/STSCI)

A supernova is the catastrophic explosion of a star. Thermonuclear supernovae, in particular, signal the complete destruction of a white dwarf star, leaving nothing behind. At least that’s what the models and observations suggested.

So when a team of astronomers went to look at the site of the peculiar thermonuclear supernova SN 2012Z with the Hubble Space Telescope, they were shocked to find that the star had survived the explosion. Not only did it survive โ€“ the star got even brighter after the supernova than before.

First author Curtis McCully, a postdoctoral researcher at the UC Santa Barbara and Las Cumbres Observatory, published these findings in an article in The Astrophysical Journal and presented them at a press conference at the 240th meeting of the American Astronomical Society. The intriguing results give us new insights into the origins of some of the most common, yet mysterious, explosions in the universe.

These thermonuclear supernovae, also called Type Ia supernovae, are some of the most important tools in astronomers’ toolkits for measuring cosmic distances. Beginning in 1998, observations of these explosions revealed that the universe is expanding at an increasingly accelerating rate. This is believed to be due to dark energy, the discovery of which won the Nobel Prize in Physics in 2011.

Although they are of vital importance to astronomy, the origins of thermonuclear supernovas are poorly understood. Astronomers agree that they are the destruction of white dwarf stars โ€“ stars with roughly the mass of the sun packed into the size of Earth. What causes stars to explode is unknown. One theory posits that the white dwarf steals matter from a companion star. When the white dwarf gets too heavy, thermonuclear reactions ignite in the core and lead to a runaway explosion that destroys the star.

SN 2012Z was a strange type of thermonuclear explosion, sometimes called a Type Iax supernova. They are the weakest and weakest cousins โ€‹โ€‹of the more traditional Type Ia. Because they are less powerful and slower explosions, some scientists have theorized that they are failed Type Ia supernovae. The new observations confirm this hypothesis.

The star that survived a supernova

Left: Color image of Galaxy NGC 1309 before Supernova 2012Z. Right: Clockwise from top right: the pre-explosion position of the supernova; SN~2012Z during the 2013 visit; the difference between the pre-explosion images and the 2016 observations; the location of SN~2012Z in the last observations in 2016. Credit: McCully et al

In 2012, supernova 2012Z was detected in the nearby spiral galaxy NGC 1309, which had been studied in depth and captured in many Hubble images over the years leading up to 2012Z. The Hubble images were taken in 2013 in a joint effort to identify which star in the oldest images matched the star that exploded. The analysis of this data in 2014 was successful – scientists were able to identify the star in the exact position of supernova 2012Z. This is the first time that the progenitor star of a white dwarf supernova has been identified.

“We were expecting to see one of two things when we got the latest Hubble data,” McCully said. “Either the star would have disappeared completely, or maybe it was still there, which means the star we saw in the pre-explosion images was not the one that exploded. Nobody expected to see a surviving star that was brighter. heads.”

McCully and the team think the half-exploded star got brighter because it swelled to a much larger state. The supernova wasn’t strong enough to blow up all the material, so some of it fell into what’s called the bound remnant. Over time, they expect the star to slowly return to its initial state, only less massive and larger. Paradoxically, for white dwarf stars, the less massive they are, the larger they are in diameter.

“This surviving star is a bit like Obi-Wan Kenobi coming back as a force ghost in Star Wars,” said co-author Andy Howell, an adjunct professor at UC Santa Barbara and senior scientist at Las Cumbres Observatory. “Nature tried to take down this star, but it came back more powerful than we could have imagined. It’s still the same star, but back in a different form. It has transcended death.”

For decades, scientists thought that Type Ia supernovae exploded when a white dwarf star reaches a certain size limit, called the Chandrasekhar limit, about 1.4 times the mass of the sun. This model has fallen out of favor a bit in recent years, as many supernovae have been found to have less mass than that, and new theoretical ideas have indicated that there are other things that cause them to explode. Astronomers weren’t sure whether the stars got close to the Chandrasekhar boundary before exploding. The study authors now think that this growth to the ceiling is exactly what happened with SN 2012Z.

“The implications for Type Ia supernovae are profound,” says McCully. “We found that supernovas can at least grow to the limit and explode. However, explosions are weak, at least sometimes. Now we need to understand what makes a supernova fail and become a Type Iax, and what makes a good one. succeeded as a Type Ia.”

Image: Hubble captures the shredded remains of a cosmic explosion

More information:
Curtis McCully et al, Even brighter than pre-explosion, SN 2012Z hasn’t disappeared: Comparing Hubble Space Telescope observations a decade apart, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac3bbd

Provided by the University of California – Santa Barbara

Quote: The star that survived a supernova (2022, June 23) recovered June 24, 2022 from

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