This star survived a supernova to continue shining bright

Challenging long held theories about supernovas.
Loukia Papadopoulos

So far, science has dictated that when a star goes through a supernova, it disappears completely. However, that may not always be the case. 

Scientists have spotted a powerful star that managed to survive a supernova to keep on shining brightly. In fact, the star was even brighter after the supernova than it had been before, according to a press release by UC Santa Barbara published on Thursday. The event is the thermonuclear supernova SN 2012Z, and the sighting was made with Hubble data.

An unexpected observation

“We were expecting to see one of two things when we got the most recent Hubble data,” first author Curtis McCully, a postdoctoral researcher at UC Santa Barbara and Las Cumbres Observatory, said.

“Either the star would have completely gone away, or maybe it would have still been there, meaning the star we saw in the pre-explosion images wasn’t the one that blew up. Nobody was expecting to see a surviving star that was brighter. That was a real puzzle.”

SN 2012Z consisted of a strange type of thermonuclear explosion, sometimes called a Type Iax supernova. This explosion is dimmer and weaker than the more traditional Type Ia. It has even been theorized that it is a failed Type Ia supernovae.

Now, observations of SN 2012Z may just confirm this theory.

SN 2012Z was first detected in 2012 in the nearby spiral galaxy NGC 1309. After careful observation over many years, the researchers believe that the half-exploded star got brighter after the supernova because it puffed up to a much bigger state.

The supernova wasn’t powerful enough to alienate all the material, so some of it fell back into what is called a bound remnant. Now, the team even expects that, over time, the star will resume its initial state. 

“This star surviving is a little like Obi-Wan Kenobi coming back as a force ghost in Star Wars,” said co-author Andy Howell, adjunct professor at UC Santa Barbara and senior staff scientist at Las Cumbres Observatory. 

"Nature tried to strike this star down, but it came back more powerful than we could have imagined. It is still the same star, but back in a different form. It transcended death.”

The Chandrasekhar limit

It was long believed that Type Ia supernovae explode when a white dwarf star reaches a certain limit in size, called the Chandrasekhar limit. But that theory has been debunked over time as many supernovae have been found to be less massive than this, and new ideas have surfaced indicating that there are other things causing them to explode.

In this case, the researchers believe that this growth to the ultimate limit is exactly what happened to SN 2012Z.

“The implications for Type Ia supernovae are profound,” said McCully. “We’ve found that supernovae at least can grow to the limit and explode. Yet the explosions are weak, at least some of the time. Now we need to understand what makes a supernova fail and become a Type Iax, and what makes one successful as a Type Ia.”

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