of all types have a single explosion. However, now a group of astronomers believe they may have found a star that exploded twice as a type 1a supernova. Artist’s concept of a white dwarf receiving material from its companion star. Credit: NASA/CXC/M. Weiss Type 1a supernovae occur in these binary systems where the white dwarf steals material from its companion star. The companion can be anything from a massive star to another white dwarf. In any case, when that white dwarf ends up stealing enough material, and exceeds the Chandrasekhar limit (1.44 times the mass of the Sun), it explodes as a supernova. The Chandrasekhar limit is simply the maximum mass that a white dwarf can have. The type 1a supernova that is attracting attention is SN 2022joj. The authors of the study explain that this star was able to explode twice and, not only that, without having to exceed the Chandrasekhar limit to explode. Stars that explode twice are rare, but a few cases have been known. They happen when the white dwarf accumulates a layer of helium that burns. In these types of explosions, the white dwarf does not exceed the Chandrasekhar limit and the explosion is quite faint.
These types of supernovae that occur twice are known as subliminal supernovae. A very striking light curve Not only the dim glow is a sign of a double supernova. It also has a rare light curve, where red light manifests 11 days before peak brightness occurs. After that peak, it looks much more like a type 1a supernova. This, along with other aspects, has led the study authors to suggest that SN 2022joj could have suffered a double detonation. At different points in their evolution, different types of stars may have shells of different chemical elements. White dwarfs are no exception.
They can have outer shells of helium or hydrogen. The vast majority of white dwarf stars have an outer shell (or atmosphere) of hydrogen. The study authors suggest that SN 2022joj has an outer shell of helium. In this case, the white dwarf’s companion star has an outer shell of helium. SN 2022joj has therefore been stealing some of that helium, forming its own outer shell. This can trigger a helium detonation, even though the star has not passed the Chandrasekhar limit. An important aspect, moreover, is that this helium explosion creates another element: an isotope of nickel called 56Ni. All of that nickel is visible in the spectrometry of the star. When the helium shell explodes, it not only synthesises 56Ni, it also causes a powerful shock wave on the white dwarf. That wave can cause another detonation inside the star. This is the mechanism that causes a double detonation supernova. Analysis of the supernova supports this explanation, according to the study authors. A model that explains how a star could explode twice The characteristics of the supernova fit with the models of a double detonation of a white dwarf that has a solar mass and a thin layer of helium around it, between 0.01 and 0 .02 solar masses. Light curves are very useful because they tell astrophysicists what is happening in a star. The same thing happens here. The light curve of SN 2022joj has allowed researchers to obtain a lot of information. The light curve, in this case, is different from that of a common type 1a supernova. Despite this, certainty is not absolute. Artist’s concept of a supernova explosion. Credit: European Southern Observatory/M. Kornmesser Researchers are not entirely sure that it is a double detonation supernova. Although there are clues that a double explosion could have occurred, other indications do not point in that direction. In the spectrum of the nebula (of the supernova) there is a strong Fe III signal, which cannot be explained by a double detonation. Therefore, according to the researchers, more detailed models will be needed. Supernovae are very important in nature, they synthesize certain metals and spread them through space when they explode. Without them, there would be no rocky planets like ours.
So type 1a supernovae are important for their role in the universe. They are believed to synthesize most elements of the iron group, from titanium to zinc. As for whether we are really looking at a star that could have exploded twice, it seems that we will have to wait a little longer to have a concrete answer. It is nevertheless interesting, in any case, to see that there continue to be surprises in all fields of astronomy, also in that of the most violent explosions in the cosmos…
Study The study is E. Padilla González, D. Howell, G. Terreran et al.; “SN 2022joj: A Potential Double Detonation with a Thin Helium shell.” It is available for consultation on arXiv, at this link.