FBOTs - Fast Blue Optical Transients are a new type of cosmic explosions. So new, that we only know of three.
Space - wast, and dark seems to be quiet, and almost dead. But in reality, it is full of dramatic cosmic explosions that destroy everything nearby with their enormous energy. And there are many kinds of explosions - it almost seems like there was a bizarre show full of destructive monsters.
Raffaella Margutti from Northwestern University in the USA and her colleagues are now bringing a new monster into the scene. And this one is almost ultra-extreme. These are Fast Blue Optical Transients (FBOT explosions) - very bright events that fire off an incredible amount of energy in a very short amount of time. FBOTs shine extremely bright in the blue visible part of the electromagnetic spectrum but we can also easily observe them in the x-ray and radio part of the spectrum. They appear suddenly and then disappear at the same rate - radiating out so much energy that it is almost unimaginable.
FBOTs are to a degree similar to other extreme cosmic explosions such as supernovae, gamma-ray bursts, and fast-radio-bursts. But they do differ in a few key parameters. For example, an FBOT happens in a much shorter period of time that's even a fast-radio-burst which itself usually lasts for a couple of milliseconds. Or another interesting difference is the fact that FBOTs include hydrogen in them while gamma-ray bursts do not
FBOTs seem to be quite rare. At this time we know only of three - "The Cow, Koala", and the CSS161010 explosion which is yet to get a cute animal nickname. The first was the "The Cow" or AT2018COW which we observed in June of 2018. It shined a hundred times brighter than a regular supernova and disappeared after just 16 days.
Just a few months later after "The Cow" astronomers tracked down an even more extreme explosion. ZTF18abvkwla or "Koala". By analyzing its radiation in the radio wave part of the spectrum they concluded that Koala was ten times brighter than The Cow. And it disappeared even faster than The Cow. But the strangest known FBOT explosion is CSS161010. We actually observed it back in 2016 but only now have experts discovered its truly extreme side. It is estimated that this explosion fired off about 10 percent of our Sun's mass at more than half the speed of light.
So... what exactly are FBOTs? Their research is quite problematic because they suddenly appear and quickly disappear. And we only found three of them. Nonetheless, they do have a few things in common. All three come from small galaxies with stars with low metallicity. And there are indications that there is either a black hole or a neutron star at the core of these explosions. This suggests that FBOTs could be a rare type of supernova. Another possibility is that they occur when a star is eaten by a black hole or possibly some other extremely energetic phenomenon. But to truly know, we will need more FBOTs to study.
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