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

The explosion of a star is called a supernova. The destruction of a white dwarf star is signaled by thermonuclear supernovae. That's what models and observations said.

Astronomers were shocked to discover that the star had survived the explosion when they looked at the site with the Hubble telescope. The star was brighter than it had been before.

The findings were published in an article in The Astrophysical Journal and presented at a press conference. The results gave us new information about the origin of some of the most common explosions in the universe.

Astronomers use thermonuclear supernovae, also known as Type Ia supernovae, to measure distances. The universe has been expanding at an ever-increasing rate since 1998. Dark energy is thought to be the reason for this.

The origins of thermo nuclear supernovae are poorly understood. The destruction of white dwarf stars is similar to the destruction of the sun. There is no known cause of the stars exploding. There is a theory that the white dwarf is a thief. A runaway explosion destroys the star when the white dwarf gets too heavy.

SN 2012Z was a type of thermonuclear explosion. They are cousins of the more traditional type. Scientists theorize that they are failed Type Ia supernovae because of their slower explosions. This hypothesis is confirmed by the new observations.

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

The supernova 2012Z was found in a spiral galaxy, which had been studied in depth and captured in many Hubble images. In order to identify which star in the older images was the one that exploded, Hubble took images in 2013). The scientists were able to identify the star at the exact location of the 2012Z supernova. The progenitor star of a white dwarf supernova was identified for the first time.

When we received the most recent Hubble data, we were expecting to see at least one thing. The star we saw in the pre-explosion images was not the one that exploded. Nobody expected a star that was not dead to be brighter. That was a challenge.

The half-exploded star puffed up to a much bigger state, and that's what the team thinks. Some of the material from the supernova fell back into a remnant. They expect the star to return to its initial state slowly. White dwarf stars with less mass are larger in size.

The co-author of the book said that the star was like Obi-Wan in Star Wars. The star came back stronger than we could have imagined. The same star is back in a new form. It didn't end.

When a white dwarf star reaches a certain size, called the Chandrasekhar limit, it's known as a Type Ia supernovae. Many supernovae have been found to be less massive than this, and new theoretical ideas have indicated that there are other things causing them to explode. Astronomers didn't know if stars got close to the Chandrasekhar limit before they exploded. The authors believe that the growth to the ultimate limit is what happened to SN 2012Z.

The implications forType Ia supernovae are profound. It has been found that supernovae can grow to the limit. The blasts are weak at times. We need to understand what makes a supernova fail and what makes someone successful as a type Ia.

More information: Curtis McCully et al, Still Brighter than Pre-explosion, SN 2012Z Did Not Disappear: Comparing Hubble Space Telescope Observations a Decade Apart, The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac3bbd Journal information: Astrophysical Journal