Scientists claim that the supernova SN 2022joj may explode for the second time. The star system in which it exploded consists of an ordinary star and a white dwarf, on which the explosion occurred. Its spectrum shows that it can happen again.
When a white dwarf explodes as a supernova
Supernovae are a phenomenon when stars explode. In many cases, the explosion is so strong that most of the luminary is completely destroyed and only a black hole or pulsar remains from it. There is another type of supernova called Ia. They occur in close binary systems consisting of an ordinary luminary and a white dwarf.
This is exactly the supernova SN 2022joj, observed by scientists last year. It exploded in a distant galaxy, but astrophysicists still managed to study the curves of its brightness. And in them, they found strange characteristics that allowed them to assume that it could explode a second time.
Usually, the explosion of a white dwarf occurs after it has pulled its material from the second star in the system for a long time. Because of this, its mass increases and at some point crosses the so-called Chandrasekhar limit. It explodes like a supernova and only a pulsar remains from it, which cannot be seen at such a great distance.
Repeated explosions
However, it is quite rare for a white dwarf to turn into a supernova twice. This is due to the fact that it does not cross the Chandrasekhar limit. However, in order for this to happen, a rather rare situation is needed. The second star should be helium.
Usually white dwarfs have an outer shell of hydrogen. However, when they are located next to a helium star, the material that comes from it forms another layer, which is filled with the second-numbered element of the periodic table. At some point, the temperature and mass of helium exceed a certain critical mark, and it explodes, similar to how it happens on massive stars at the end of their existence.
A helium explosion causes a powerful shock wave that shakes the entire white dwarf and leads to other detonation processes. We see this event as a slightly dim type Ia supernova. After it fades out, the white dwarf continues to pull material from the companion star.
Whether SN 2022joj will explode for the second time
The idea that the supernova SN 2022joj could explode for the second time was suggested to scientists not only by the dimness of this supernova, but also by its unusual spectrum before the explosion. An unusual double peak of radiation was observed 11 days before the event. It started as red, but gradually shifted to the blue side. This is what scientists expected to see in the case of a helium explosion.
However, there is something in this supernova that does not fit into the proposed scenario. When a white dwarf explodes again, the isotope nickel-56 should be formed from helium. Type Ia is generally one of the main suppliers of heavy elements in the Universe.
However, in SN 2022joj, lines of twice ionized iron were noticed. It should not have been formed in such a scenario, and it is unclear where it came from. However, scientists are still convinced that their proposed explanation is correct.
According to phys.org
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