The star survives a violent supernova and becomes even brighter

A supernova is a bright, catastrophic star explosion. In particular, so-called thermonuclear supernovae signal complete destruction of a white dwarf star and leave nothing. At least that’s what computer models and space observations have suggested so far.

However, data from the Hubble Space Telescope have given a team of astronomers an unprecedented view of a particular thermonuclear supernova called SN 2012Z. They were shocked to discover that the star had survived the explosion. And more than that: the white dwarf not only survived, but its glow became even stronger.

Color images of the spiral galaxy NGC 1309 before and after the explosion of SN 2012Z. The left frame shows the pre-explosion image. The four panels to the right show the evolution of the supernova during the observations. Photo: NASA, ESA, Hubble Heritage Team (STSCI / AURA) and A. Riess (JHU / STSCI)

An article published in the scientific journal The Astrophysical Journal reports the results of the team led by Curtis McCully, a postdoc researcher at the University of California-Santa Barbara and the Las Cumbres Observatory. Their exciting results provide new insights into the origins of some of the most common – and mysterious – explosions in the universe.

Also called type Ia supernovae, thermonuclear supernovae are among the most important tools used by astronomers to measure cosmic distances. Since 1998, observations of these explosions have revealed that the universe is expanding at an ever-accelerating speed, which is attributed to a phenomenon called dark energy.

While thermonuclear supernovae are crucial to astronomy, their origins are still poorly understood. One theory claims that the white dwarf steals matter from a companion star. When the white dwarf becomes too heavy, thermonuclear reactions ignite in the nucleus, leading to a runaway explosion that destroys the star.

Supernova discovered compatible with type Iax

A weaker cousin of type Ia supernovae, SN 2012Z belongs to type Iax. Because they are less powerful and slower explosions, some scientists have theorized that Iax supernovae are failed Type Ia supernovae. The new observations confirm this hypothesis.

For years, the Hubble Telescope has been studying a spiral galaxy located 100 million light-years from Earth called NGC 1309. In 2012, SN 2012Z was discovered in this galaxy. During a study to determine which star in previous images caused the big bang, data analysis showed it was still there. This is the first time that the stem star of a white dwarf supernova has been identified.

“No one expected to see a brighter surviving star. It was a real headache,” McCully said, revealing that his team believes the “half-exploded” star became brighter because the supernova was not strong enough to blow up all the material in the air, so a part has fallen back to what it is. called rest.

Over time, they expect the star to slowly return to its original state, only less massive and larger. For white dwarf stars, the smaller they are, the larger their diameter.

“Nature tried to overthrow this star, but it came back stronger than we could have imagined,” said co-author Andy Howell, assistant professor at UC Santa Barbara and senior researcher at the Observatory of Las Cumbres. “It’s still the same star, but back in a different form. She passed away.

For decades, scientists believed that Type Ia supernovae exploded when a white dwarf star reached a certain size limit, called the Chandrasekhar limit, or about 1.4 times the mass of the Sun.

This model has fallen into disfavor in recent years, as many supernovae have proven to be less massive than this, and new theoretical ideas have indicated that there are other things that are causing them to explode. Astronomers did not know if the stars were approaching the Chandrasekhar boundary before they exploded.

The authors of the new study believe that this growth at the ultimate limit is exactly what happened with SN 2012Z. “The implications for Type Ia supernovae are profound,” McCully says. “We found that supernovae can at least reach the limit and explode. However, the explosions are weak, at least sometimes. Now we have to understand what makes a supernova fail and become Type Iax, and what does the successful as Type Ia.

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