A white dwarf survived his supernova explosion by becoming a “zombie” star

In about two weeks Nasa will publish the first spectroscopic images and data from James Webb Space Telescope makes it possible to begin the collection of scientific information with this new one eye on orbit of the noosphere. But the Hubble Telescope, its predecessor, has not yet said its last word, either with new observations or by analyzing in a new way those it has made in the past and which are archived for future generations.astrophysicists.

At this last point, a new proof of has just been given Curtis McCullya postdoc researcher at UC Santa Barbara and the Las Cumbres Observatory, who, along with his colleagues, published an article in the famous The Astrophysical Journal. Available at arXivit contains results from observations made with Hubble in the years 2000-2010, which were presented at a press conference on the occasion of the 240th.e meeting of the American Astronomical Society.

The researchers announced there that they had confirmed the existence of a new type of thermonuclear supernovae, a variant of the type of supernovae NS Ia produced with white dwarfs and which is called SN Iax. Less powerful than their cousins, but more than simple novices, they do not lead to the destruction of their star parent, and it’s a surprise that obscures our understanding of supernovae with white dwarfs.

SN Iax took place in January 2012 in the form of supernova SN 2012Z has been discovered within the framework of the research program Lick Observatory Supernova Searchin spiral galaxy neighbor to The Milky Way, NGC 1309

A supernova zoo

But before we examine this discovery further, let’s take a look at some explanations already given by Futura in a previous article. It is about what has been called for centuries Tycho Brahe and Johannes Keplerfamous builders of Heaven, “new stars”, abbreviated to novae, from Latin stella-nova which means “new star”. But it was not until the 1930s and the work of Walter Baade and Fritz Zwicky that we realized the differences between novices and supernovae. The first subclasses of today’s famous supernovae, SN I and SN II of the famous classification designed byastronomer German-American Rudolph Minkowski and Swiss astronomer Fritz Zwicky.

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

SN Ia are thermonuclear explosions of white dwarfs in binary systems while the much more powerful SN IIs are explosions produced by stars that are much heavier than Sun and which collapse gravitationally neutron starsor some black holes if they are large enough. In any case, the differences between supernovae (others would still be highlighted to this day) are on par with spectrum reflects the presence of certain elements in light explosions and in the variations and durations brightnesses (light curves) of these stellar disasters.

Classic SN Ia

Thus, type I supernovae have a spectrum that does not contain hydrogen, while type II supernovae have a spectrum that does. Among type I supernovae, three subclasses are distinguished so that if the spectrum shows the presence of silicon, we are talking about type Ia, but if the spectrum does not show any, we are looking at the abundance of helium. In the presence of a significant amount of He, one speaks of type Ib and conversely, in the presence of a small amount of helium, one speaks of type Ic.

The SN Iax type has therefore just been introduced for a few years now.

An animation showing the default model for an SN Ia, see explanations below. © Caastro

The classic model for an SN Ia was the following. It all starts in a binary system where one star is slightly more massive than the other but does not exceed 8 to 10 masses solar cells, evolve faster by first becoming one red dwarf. This leads to her losing a lot with win violent, to end up leaving a stellar in the form of a white dwarf containing less than 1.44 times the mass of the Sun.

If the two stars are close enough to each other when the other becomes a red giant again, it will tidal forces the gravity of the first mass from it. It forms one accretion disk around the white dwarf, which sees its mass increase by sinking, to form its outer layers, hydrogen and helium, while its core contains a mass carbon and oxygen. A series of thermonuclear reactions start when the mass of the white dwarf reaches 1.44 times the mass of the Sun, and a thermonuclear explosion then occurs, which completely destroys the white dwarf and leaves a supernova-restas can be seen in the animation in the video above.

A zombie star produced by an SN Iax

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

Finally, for some years, after being able to assess the mass of white dwarfs spawning supernovae SN Ia, it was discovered that it was lower than mace of chandrasekharso it has become necessary to review the mechanisms behind the thermonuclear explosion.

Surprisingly, in the case of SN 2012Z, the white dwarf not only survived an explosion in supernova mode, but it became brighter as seen in the insertion to the right of the image above, suggesting an increase in size. This phenomenon has been described as a “zombie” star, as it has somehow come to life again, while it basically remained the body of a star once on the main sequence.

One type of Iax supernova is less bright, and its light curve evolves more slowly, leading nuclear astrophysicists to believe that SN 2012Z was somehow a failed supernova whose details of thermonuclear reactions behind the explosion are still poorly understood. . It’s really disturbing, and at the moment it defies previous models of SN Ia, because in the case of SN 2012Z, the explosion happened with a tribal star, which we could identify on images from the Hubble archives, and whose mass was close to Chandrasekhars. Better yet, this is the first time that the white dwarf ancestor of a supernova has been identified.

In the UC Santa Barbara Declaration accompanying the discovery, McCully concludes that “ the implications for Type Ia supernovae are deep. We found that supernovae can at least grow to the extreme and explode. Still, the explosions are weak, at least some of the time. Now we need to understand what makes a supernova fail and become type Iax, and what makes a supernova succeed as type Ia “.

Are you reading ideas for the summer with Futura?

To celebrate the start of the holiday, we offer you Mag Futura at the advantageous price of 15 € instead of 19 €, ie. a reduction of 20% !

What is Mag Futura?

  • Our first paper journal of more than 200 pages to make science accessible to as many people as possible
  • 4 major scientific questions for 2022, from Earth to the Moon
  • Home delivery *

* Special offer valid until 19 July. Delivery takes place in France (excluding the metropolitan area of ​​France), Switzerland, Belgium.

Interested in what you just read?

Leave a Comment