A white dwarf survived a supernova explosion to become a ‘zombie’ star

In about two weeks, a file NASA will make the audience First images and spectroscopic data The James Webb Space Telescope Letting start collecting scientific information with this new eye on me orbiting Noosphere. But the Hubble telescope, which preceded it, has not yet said its last word, either through new observations or through analysis in a new way to those it has done in the past and which have been archived for future generations.astrophysicists.

On this last point, a new guide was introduced by Curtis McCauleya postdoctoral researcher at the University of California, Santa Barbara and the Las Cumbres Observatory, who together with his colleagues published an article in the famous journal Astrophysical Journal. Available at arXivcontains results from observations made with Hubble during the years 2000-2010 and which were presented at a press conference on the occasion of 240e American Astronomical Society meeting.

Researchers there announced that they had confirmed the existence of a new type of thermonuclear supernova, a different type of supernova. NS Ia produced with white dwarfs which are called SN Iax. Less powerful than their cousins, but more than simple supernovae, they do not lead to destruction star It is a surprise that confuses our understanding of white dwarf supernovae.

SN Iax happened in January 2012, in the form of Supernova SN 2012Z was discovered under the research program Lick Observatory Supernova Searchin spiral galaxy neighbor Milky WayAnd the NGC 1309.

Supernova Zoo

But before examining this discovery more closely, let’s take a look at some of the explanations already given by Futura in a previous article. It’s about what has been called for centuries since then Tycho Brahe And the Johannes KeplerFamous Heaven Builders, “New Stars”, and shortened to noveAnd the from latin Stella Nova It means “new star”. But it wasn’t until the 1930s and the works of Walter Bade and Fritz Zwicky that we realized the differences between supernovae supernovae. Soon the first subclasses of the supernovae that are popular today, SN I and SN II of the famous classification designed by him, were discovered.astronomer German-American Rudolf Minkowski and Swiss astronomer Fritz Zwicky.

Excerpts from the documentary From the Big Bang to the living (ECP Productions, 2010). Jean-Pierre Lumenet talks about the evolution of stars of the solar type, their transformation into red giants, and then into white dwarfs. © Jean-Pierre Luminet

SN Ia are thermonuclear explosions of white dwarfs in Binary systems Whereas the much more powerful SN IIs are explosions produced by stars much heavier than Sun And that crumbles the attractiveness of tender neutron starsor some black holes If it is big enough. In any case, the differences between supernovae (others will be highlighted to this day), are at the level Domain Which reflects the presence of some elements in light Explosions, variations and durations The luminous intensity (light curves) of these stellar catastrophes.

Classic SN Ia

Thus, type I supernovae have a spectrum that does not contain hydrogen while type II supernovae have a spectrum that does not contain hydrogen. Among Type I supernovae, three subclasses are distinguished, so that if the spectrum showed the presence of siliconWe’re talking about Type Ia but if the spectrum doesn’t show anything, we’re looking at the abundance of helium. In the presence of a large amount of He, one speaks of type Ib and vice versa, in the presence of a small amount of helium, one speaks of type Ic.

So the SN type Iax was introduced a few years ago now.

An animation showing the standard form of SN Ia, see explanations below. © Castro

The classic model of SN Ia was next. It all starts in a binary system where one star is slightly larger than the other, but no more than 8 to 10 masses Solar cells develop more quickly when they first become red dwarf. This leads to a loss of mass winds violently, ending up leaving an A-shaped astral corpse white dwarf It contains less than 1.44 times the mass of the Sun.

If the two stars are close enough to each other when the second star in turn becomes a red giant, then tidal forces The gravitational pull of the first snatch of it. form a Accumulation disk around a white dwarf whose mass is increased by swallowing, to form its outer layers, hydrogen and helium while its core contains a lot of carbon and oxygen. A series of thermonuclear reactions starts to race when the white dwarf’s mass reaches 1.44 times the mass of the Sun, and then a thermonuclear explosion occurs, completely destroying the white dwarf and leaving supernova remnantsAs evidenced by the animation in the video above.

Zombie Star was produced by SN Iax

This image began to blur about a decade ago. It was initially suspected that some SN Ia are actually occasional collisions of white dwarfs, and in fact, Notes support this scenario.

Finally, for several years, after being able to assess the mass of white dwarfs that spawn SN Ia supernovae, it was discovered that it was less than chandrasekhar scepterso that it became necessary to review the mechanisms underlying thermonuclear explosion.

Surprisingly in the case of SN 2012Z, the white dwarf not only survived a supernova-mode explosion, but also became much brighter as seen in the interior to the right of the image above, indicating an increase in size. The phenomenon has been described as a “zombie” star because it somehow came back to life, while essentially remaining the body of a star once in the main sequence.

A Type Iax supernova is less bright and its light curve develops more slowly, leading nuclear astrophysicists to believe that SN 2012Z was somehow a failed supernova, and the details of the thermonuclear reactions behind the explosion are still poorly understood. It’s really annoying, and for now, it challenges previous models of SN Ia because, in the case of SN 2012Z, the explosion occurred with a progenitor star that we can identify in images from the Hubble archives, whose mass was close to that of Chandrasekhar. Even better, it’s the first time that one gets to know the white dwarf ancestor of a supernova.

In the University of California Santa Barbara statement accompanying the discovery, McCauley concludes that “ The implications for Type Ia supernovae are profound. We found that supernovae, at least, can grow to the limit and explode. The bangs are still weak, at least for a while. We now need to understand what makes a supernova fail as a Type Iax, and what makes a supernova succeed as Type Ia “.

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