500 million light years from Earth, astronomers have observed a supernova caused by a cosmic collision.
It’s a first. Astronomers have detected a phenomenon that was until then only at the theoretical stage: a supernova generated by the collision of a star with a black hole, or a neutron star. Their study was published in the journal Science on September 3.
Well, it’s not the easiest cosmic phenomenon to understand but already, what is a supernova? It is the explosion of a star which then gives off a light whose power is comparable to that of an entire galaxy, or hundreds of billions of stars. There are two families of supernovae: SN II and SN Ia.
This set of phenomena following the implosion of a star at the end of its life unfold according to possible scenarios:
– or by the thermonuclear explosion of a white dwarf star following an accretion of matter torn from a neighboring star (or even a collision with the latter).
The case detected by astronomers is the first: it is therefore a supernova called “heart failure”. Understand: at the end of life. “She’s a star dying of old age,” says Dillon Dong, a researcher at the California Institute of Technology (Caltech) and lead author of the study. “Theorists had predicted that it could happen, but this is the first time that we see one,” he said.
The event occurs when a massive star depletes its hydrogen, and can no longer continue thermonuclear reactions. Crushed under its own weight, it eventually collapses on itself, before exploding violently. “What we have found is that massive stars can actually die much sooner,” the researcher comments.
By analyzing radio signals collected by the Very Large Array Sky Survey, aka “VLASS” in 2017 and 2018, they found a peak in radiation much more intense than the others. They then delved into the archive data, and managed to link it with an explosion of gamma rays coming from the same place … in 2014. In this way, they were able to trace the whole history of this phenomenon which has started … 300 years earlier.
Gregg Hallinan, researcher at Caltech retraces his journey which corresponds to the 4 stages schematized above: “The sequence of events can be read clockwise, starting from the top left: the neutron star or the black hole orbits around its “normal” companion star (light blue). (1) After getting sufficiently close, the neutron star or black hole enters the atmosphere of its companion, throwing gas towards it. outside in an expanding spiral. (2). When the intruder reaches the core of the companion, the material briefly forms a disc which propels an ultra-rapid jet outwards. Nuclear fusion which held the core of the star against its own gravity is disrupted, triggering a collapse and subsequent supernova explosion. (3) The material thrown by the supernova explosion catches up with the material thrown by the previous interaction (2014), causing strong waves of shock that produce radio waves dating from 2017. “
Because beyond the discovery, it is the very interest of VLASS, which makes it possible to identify and catalog millions of radio signals not yet attributed to particular phenomena, which is put forward.