An Israeli researcher discovered an unusual supernova

The source is apparently a new type of cosmic explosion - a rare coincidence in which double stars interfere with each other's development

In an article published in the express edition of the journal Science on Thursday, November 5, a group of researchers led by Dr. Dobi Poznansky from the University of Berkeley in California reports on the supernova named 2002bj and that it seems to be a new type of explosion.

"We have never seen a supernova so fast," says Poznansky, a postdoctoral student at Berkeley and a graduate of the astrophysics department at Tel Aviv University, "within three weeks it simply disappeared, many times faster than any supernova we have ever seen."

However the supernova was not very bright, and its spectral signature is very unique. "Helium, carbon, sulfur, maybe vanadium - a rare element that we have never detected in a supernova, everything points to a thermonuclear explosion of helium."

In a conversation with the science website, Poznansky says that the reason for the rarity of these supernovae is that not every star can develop a type Ia supernova. (point 1 and a), but only stars that are in a double system, and in unique circumstances. "Each star consumes hydrogen and then burns the helium and heavier elements, but ordinary stars, which would become white dwarfs, were usually white dwarfs made of carbon and oxygen. Only in binary systems where the stars interfere with each other's evolution can a helium white dwarf form. And this, only if the distance between them and the rate of absorption of the material are suitable, the conditions suitable for supernova "Ia" can be created.

"Supernovas of this type are also very fast. Not many surveys track changing objects, looking for phenomena that appear and disappear so quickly. This is actually a new field that was technologically difficult to carry out. The survey in his archives that revealed this phenomenon found 800 supernovae over 10 years, and only one was like this. If the survey was done using more modern telescopes of the type we are building today, we could find many more supernovae of this type." Poznansky explains.

"The observational differences between 2002bj and "normal" supernovae are not dramatic, but they are unequivocal," says Prof. Dan Maoz, head of the astrophysics department at Tel Aviv University.
Prof. Alexey Filippenko from Berkeley, one of the senior researchers in the field of supernovae and a partner in the study clarifies: "There are two basic types of supernovae: Ia which originate from the full explosion of a white dwarf type star, and core collapse supernovae in which a massive star consumes its nuclear fuel and collapses under the influence of its own gravity. 2002bj does not fit any of these scenarios.”

A white dwarf is a star formed at the end of the life of a normal star (like the sun for example). These stars are small and very compact. If the mass of a white dwarf increases beyond a certain limit (for example by absorbing material from a nearby star) it may explode - this is an Ia supernova. The other types of supernovae occur when stars much heavier than the Sun (at least 8 times) gravitationally collapse at the end of their lives.

Supernova 2002bj was discovered in 2002 and was mistakenly classified as a normal type II supernova. While examining data from such supernovae to measure the acceleration of the universe, Poznansky found 2002bj and was struck by its uniqueness. The supernova brightened in less than a week but faded over the next three weeks. In comparing the spectrum (a kind of chemical stamp; an indication of the materials and conditions in the observed essence) of 2002bj from the Keck telescope to about 1,400 other supernovae, it has no counterpart.

A search of the astronomical literature revealed a possible explanation. In a study published about two years ago, Prof. Lars Bildsten from the University of Santa Barbara, California, and his partners hypothesized that a pair of white dwarfs in a particular array called AM-CVn after the first star of this type to be discovered, may produce a "miniature" supernova. In these stars, helium flows from the smaller of the two white dwarfs towards its partner. When enough helium is collected on the edge of the star, the pressure and temperature conditions necessary for helium fusion are created in a short time. This explosion is expected to appear as a very fast supernova, but pales in comparison to the Iargilla supernova.

In a semi-Hethonian way, these supernovae were called ".Ia" (point one A) because they are about one-tenth the brightness and about one-tenth the time of supernova Ia. "One of the clues is that according to the calculations in ".Ia" supernovae, chromium can be formed that fades into lundium and then into titanium," says Poznansky, "this almost fits too well with our observations."

Prof. Dan Maoz adds: "For several years now, several groups of researchers have been looking for type ".Ia" supernovae and the like. It is amusing that Dovi found the most convincing example precisely in the data from seven years ago."
Prof. Bildsten is very excited: "The sky is the limit, so usually observers are ahead of the theory, which is why I am very proud of our research and predictions. Although the observations were made in 2002, Poznansky's inquisitive look was required in order to recognize the importance of the data and the discovery."

Later in his conversation with the science website, Poznansky says that these days a new and relevant Palomar Transient Factory survey is being conducted. This observatory belongs to the California Institute of Technology, and Poznansky is a partner in it along with many of the co-authors of the article. The survey is carried out using a large CCD camera that scans large areas of the sky every night. This camera is connected to a relatively small telescope - one and a half meters in diameter at Mitzpe Plumer. "The telescope is not big, but the camera is huge and this combination allows us to scan large parts of the sky every night. The survey began about six months ago and is planned to operate for at least three years.