In about two weeks, thewill make public from allowing to begin the collection of scientific information with this new on of the noosphere. But the Hubble telescope, its predecessor, has yet to say 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. of .
On this last point, a new proof has just been given bya postdoctoral researcher at UC Santa Barbara and the Las Cumbres Observatory, who published with his colleagues an article in the renowned The Astrophysical Journal. Available on it contains results from observations carried out with Hubble during the years 2000-2010 and which were presented at a press conference on the occasion of the 240e 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 type supernovaeIa produced with white dwarfs and which are called SN Iax. Less powerful than their cousins, but more than simple novae, they do not lead to the destruction of their parent and it is a surprise that blurs our understanding of supernovae with white dwarfs.
The SN Iax occurred in January 2012, in the form of the Lick Observatory Supernova Searchin neighbor of the , 1309.SN 2012Z having been detected within the framework of the research program
A supernova zoo
But before examining this discovery more closely, let’s take a look at some explanations already given by Futura in a previous article. It concerns what has been called for several centuries sinceet famous builders of Heaven, “new stars”, abbreviated to , from latin new star 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 novae and . Quickly, were also discovered the first subclasses of supernovae today famous, the SN I and the SN II of the famous classification designed by the German-American Rudolph Minkowski and Swiss astronomer Fritz Zwicky.
Excerpt 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, then into white dwarfs. © Jean-Pierre Luminet
SN Ia are thermonuclear explosions of white dwarfs inwhile the much more powerful SN IIs are explosions produced by stars much heavier than the and which collapse gravitationally giving or some if they are big enough. In any case, the differences between supernovae (others were going to be highlighted until our days still), are at the level of the reflecting the presence of certain elements in the explosions and in the variations and luminous intensities (curves of light) of these stellar cataclysms.
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, we speak of type Ia but if the spectrum does not show any, we look at the abundance of helium. In the presence of a significant quantity of He, one speaks of type Ib and conversely, in the presence of a small quantity 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 standard 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 a star a little more massive than the other, but not exceeding 8 to 10solar cells, evolves more rapidly by first becoming a . This leads her to lose mass with violent, to end up leaving a stellar corpse in the form of a containing less than 1.44 times the mass of the Sun.
If the two stars are close enough to each other when the second one in turn becomes a red giant, thegravity of the first snatch mass from it. It forms a around the white dwarf which sees its mass increase by swallowing, to form its outer layers, hydrogen and helium while its core contains a lot of and oxygen. A series of thermonuclear reactions start racing when the mass of the white dwarf reaches 1.44 times that of the Sun and a thermonuclear explosion then occurs, completely destroying the white dwarf and leaving a as can be seen in the animation in the video above.
A zombie star produced by an SN Iax
This picture began to blur about a decade ago. It was first suspected that some SN Ia are in fact sometimes collisions of white dwarfs and, in fact,.
Finally, for some years, after being able to evaluate the mass of white dwarfs spawning supernovae SN Ia, it was discovered that it was lower than theso that it has become necessary to review the mechanisms behind the thermonuclear explosion.
Surprisingly in the case of SN 2012Z, not only did the white dwarf survive an explosion in supernova mode but it became brighter as seen in the inset to the right of the photo above, suggesting an increase in size. This phenomenon has been described as a “zombie” star since it has somehow come back to life, while basically remaining the corpse of a star once on the main sequence.
A type 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, for the moment, it defies previous models of SN Ia because, in the case of SN 2012Z, the explosion did occur with a progenitor star that we could identify on images from the Hubble archives, and whose mass was close to that of Chandrasekhar. Better, it is the first time that one identifies the white dwarf progenitor of a supernova.
In the UC Santa Barbara statement accompanying the discovery, McCully concludes that “ the implications for Type Ia supernovae are profound. We found that supernovae, at least, can grow to the limit 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 ».