The trigger of a mysterious cosmic kaboom has led to the classification of a new sort of space explosion nicknamed “the Cow” (AT2018cow).
This is an uncommon sort of core-collapse supernova that led to the formation of a compact cosmic object, both a neutron star or a small black hole.
The Cow was detected on 16 June 2018, and was immediately fascinating. It was incredibly brief, and incredibly bright, around 100 times brighter than a typical supernova. Due to the brightness initially it was thought to be coming from within the Milky Way. Astronomers were stunned when they figured out it actually emanated from a galaxy 200 million light-years away.Since the Cow, more explosions with a similar profile have been identified. They have been named Fast Blue Optical Transients, of FBOTs, and astronomers have been keen to get to the bottom of what causes them.
The data from NASA’s X-ray Telescope Neutron Star Interior Composition Explorer (NICER), which is attached to the International Space Station was analyzed.
In those data, the researchers found that something within the Cow was pulsing in soft X-rays, letting out a burst every 4.4 milliseconds, for the entire duration of the 60-day observing period. This periodicity sets pretty stringent constraints on the physical mechanism producing the X-rays; whatever it is can be no larger than 1,000 kilometers (621 miles) across.
The strength of the signal placed constraints on the object’s mass. It can be no greater than 800 times the mass of the Sun, which rules out tidal disruption of an intermediate-mass black hole. This suggested a core-collapse.
The periodic pulsations could be produced by different mechanisms, depending on what the compact object is. If it’s a neutron star, 4.4 milliseconds could be its spin rate. If it’s a black hole, the emission could be produced by fallback – material blasted out during the supernova falling back into the new-born black hole, generating X-ray emissions.
There are still some unanswered questions. Future studies of the Cow and other FBOTs could help to resolve these outstanding problems.