The faintest supernova ever seen has been spotted in a galaxy about 88 million light years away. It is so dim that it doesn鈥檛 seem to fit existing models produced to explain the faintest supernovae.
at the California Institute of Technology and his colleagues found the cosmic explosion, called SN 2021fcg, using the in California. At its peak, it put out about three times less than the previous record holder for faintest supernova.
鈥淚t鈥檚 at least 100 times fainter than a normal supernova of this type,鈥� says Karambelkar. 鈥淏ut even though this is dim for a supernova, it鈥檚 still 10 million times brighter than the sun.鈥�
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Generally, this kind of supernova, called a type Ia, occurs in binary star systems where a white dwarf gradually pulls matter from its companion star until it becomes too massive to support itself, at which point it explodes. However, SN 2021fcg is too dim to have formed via that mechanism.
There are two models that could explain its dimness. The first, which has been proposed for other unusually faint supernovae, is that a particular type of white dwarf could partially ignite, blowing off some of its plasma without completely exploding. However, that process is expected to create explosions about three times brighter than this one. The other model involves a white dwarf with a core made of carbon and oxygen smashing into another with a core of oxygen and neon, but is expected to cause explosions about three times dimmer than this one.
鈥淪N 2021fcg remains between these two, so it remains to be seen whether we can get either of those models to match this explosion,鈥� says Karambelkar. 鈥淲e were already struggling with explaining the luminosities of these [dim] supernovae, and now we have one that鈥檚 even fainter, so it鈥檚 a problem.鈥�
We will need more observations of faint supernovae and more detailed models to solve the problem, he says.
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