Generally, discoveries in astrophysics are first predicted by theoretical scientists, and only later can someone observe and prove that prediction. This is the case of a bizarre supernova detected in 2017 and understood only now, with the publication of a new study in the journal Science.
It was during a survey of the Very Large Array Sky Survey (VLASS) radio telescope in 2017 that a very bright radio source was detected in a region where there was nothing in previous surveys conducted with the same instrument. The researchers analyzed data from the WM Keck Observatory, which studies the sky at optical and infrared wavelengths, and found there was a candidate for a supernova remnant.
However, it was not an ordinary supernova. First, the remaining material was expanding, interacting with dust and gas, causing shocks and generating heat. This produced electromagnetic radiation so bright that it is easy to detect, even if the event occurs in other galaxies.
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So the team of astronomers tracked the phenomenon, dubbed VT J121001+4959647, to a dwarf galaxy 480 million light-years away. If the event was a supernova, older data should reveal a star at the site, so they looked for data from previous surveys, and found a soft X-ray burst detected in 2014 by the Monitor of All Sky X-ray Image (MAXI) instrument , which is on the International Space Station.
These data were enough for the team to be able to describe the strange supernova, never seen before. The exploded star was probably part of a binary system, meaning there were two stars orbiting each other. One of them was more massive, so it collapsed first, becoming a neutron star or even a black hole.
The second star continued to do its star thing—that is, fuse elements at its core—but its companion (which was now a neutron star or black hole) was still around and in the same orbit. As the two objects gradually spiraled toward a collision, the dead star began to suck material from its still-living sister.
When the material from the lighter star is pulled by the companion, it ends up spreading out in all directions, forming a torus of gas and dust orbiting the two objects. This process started about 300 years ago, according to the research, until they finally met and started to merge.
This collision was not a quick and simple thing, because before the collision is complete, the core of the smaller star broke, due to the high gravity of the dead companion. This stopped the living star’s nuclear fusion process, which provides the external pressure needed to remain stable. In other words, the core collapsed and the star exploded in a supernova, but not before the broken core forms an accretion disk around the big sister.
Accretion disks can be highly energetic — in fact, it’s usually thanks to them that astronomers can detect a black hole. Another phenomenon that can occur in these cases is the emission of a relativistic jet, and that’s exactly what happened to the dead object. The jet passed through all the chaotic material around the binary system and projected itself into space.
Well, it was this bright jet that produced the X-ray glow detected by the MAXI instrument in 2014. The radio wave glow detected by the VLASS in 2017 was caused by the material ejected by the supernova, which exploded quickly at the end of the whole messy process. When the supernova material, at high speed, caught up with the previous material (the material released by the ruptured core), it crashed into it, causing it to glow.
Finally, the star’s explosion seemed inevitable, even if her dead companion wasn’t around, though she might live a little longer if she were a lone star. “All the pieces of this puzzle fit together to tell this incredible story,” said Caltech astronomer Gregg Hallinan. The article with the results was published in the journal Science.
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