Sunday, August 7, 2022

Strange star that survived thermonuclear supernova

A supernova is a cataclysmic explosion of a star. The thermonuclear supernova explosion of a white dwarf is believed to be the last event in the life of its progenitor star.

These thermonuclear supernovae, known as Type Ia supernovae, are some of the most important tools in astronomers’ toolkits for measuring cosmic distances. It is believed that the explosion completely opens the star to normal Type Ia supernovae (SN Ia), which are used as a standard candle for cosmology.

A team of astronomers examined the site of the peculiar thermonuclear supernova SN 2012Z with the Hubble Space Telescope. In a shocking revelation, he discovered that the star had survived the explosion.

Not only did it survive, but after the supernova the star was even brighter than it was before.

First author Curtis McCully, a postdoctoral researcher at the University of California, Santa Barbara and Las Cumbres Observatory, presented these findings at a press conference at the 240th meeting of the American Astronomical Society and published them in an article in The Astrophysical Journal.

The puzzling results provide new information about the origins of some of the universe’s most common yet mysterious explosions. It also clarified that there is a wider variety of white dwarf supernovae than the typical SN Ia.

Despite their significant importance to astronomy, the origins of thermonuclear supernovae are poorly understood. Astronomers agree that they are annihilating white dwarf stars (stars roughly the mass of the Sun packed into the size of Earth).

What caused the destruction of the white dwarf?

The reason is unknown. One theory suggests that the white dwarf steals matter from a companion star. When the white dwarf becomes too heavy, thermonuclear reactions ignite in the core, triggering a runaway explosion that destroys the star.

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What could be the reasons behind the survival and brightness of the star?

“Type Iax supernovae (SNe Iax) comprise the most populous class of peculiar white dwarf supernovae. Based on the prototype SN 2002cx, these are sub-luminous, low-velocity explosions compared to typical SNe Ia. Specifically, There is growing evidence that SNE IX may not destroy the star entirely, but may instead leave behind a bound remnant, in contrast to the expected complete disruption in SNE Ia, the study noted.

McCully and team think the semi-exploded star brightened as it reached a much larger state. The supernova wasn’t strong enough to blow away all the material, so some of it fell back into what’s called the bound remnant. Over time, they expect the star to gradually return to its initial state, only less massive and larger. Paradoxically, for white dwarf stars, the smaller their mass, the larger their diameter.

“This star survivor Obi-Wan Kenobi is coming back as a force ghost in Star Wars,” said co-author Andy Howell, assistant professor at UC Santa Barbara and senior staff scientist at Las Cumbres Observatory. “Nature tried to bring down this star, but it came back much more powerful than we imagined. It is still the same star, but back in a different form. It surpassed death.”

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Left: Color image of galaxy NGC 1309 before supernova 2012Z. Right: Clockwise from top right: supernova pre-explosion position; During the visit SN ~ 2012Z 2013; Differences between pre-explosion images and 2016 observations; The location of SN~2012Z in the latest comments in 2016. PHOTO CREDIT: MCCULLY ET AL.

For decades scientists thought that Type I supernovae explode when a white dwarf star reaches a certain limit in size, called the Chandrasekhar limit, which is about 1.4 times the mass of the Sun. This model has fallen out of favor somewhat over the years, as many supernovae are less massive than this, and new theoretical considerations have indicated that there are other things that are causing them to explode. Astronomers were unsure whether the stars ever approached the Chandrasekhar limit before the explosion. The authors of the study now think that this end-to-end increase is exactly what happened in SN 2012Z.

“The implications for a Type Ia supernova are profound,” says McCully. “We have found that supernovae can grow and explode, at least to the extent possible. Yet explosions are debilitating, at least occasionally. Now we need to understand why supernovae fail and Type Iax becomes, and what succeeds as Type I.”

Futuristic Approach:

“We encourage others to use our observations as constraints on their simulations to better understand the physical mechanism that produces SNE IX.” study is mentioned.

journal reference

  1. Curtis McCully, Saurabh W Jha, Richard A. Scalzo, D. Andrew Howell, Ryan J. Foley, Yaotian Zeng, Zheng-Wei Liu, Griffin Hosenzadeh, Lars Bildstein, Adam G. Rees, Robert P. Kirshner, GH Marion and Yasavo Camacho-Neves. Still brighter than pre-eruption, SN 2012Z did not disappear: a decade apart compared to Hubble Space Telescope observations. The Astrophysical Journal, Volume 925, No. 2. DOI: 10.3847/1538-4357/ac3bbd

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