New class of cosmic explosions discovered
Astronomers have discovered a new class of cosmic blasts with similar attributes to some supernovae (explosions of massive stars) and gamma-ray bursts, but also with significant differences.
The saga began in June of 2018 when astronomers saw a cosmic blast unlike any other seen before. The object, dubbed AT201cow ("The Cow"), drew worldwide attention from scientists and was studied extensively.
The Cow was a very powerful astronomical explosion, 10-100 times brighter than a normal supernova and occurred approximately 200 million light-years away in the Hercules constellation.
While the explosion shared some behaviours with supernova explosions, it differs in important aspects, particularly its unusual brightness and how rapidly it brightened and faded in just a few days.
Two additional blasts - one from 2016 and one from 2018 - also showed unusual characteristics
Two new explosions have recently been discovered called CSS161010, occurring in a galaxy about 500 million light-years from Earth, and ZTF18abvkwla ("The Koala"), occurring in a galaxy about 3.4 billion light-years away.
Both explosions were recorded using visible-light telescopes to scan large areas of night sky every evening.
Follow-up observations from the National Radio Astronomy Observatory indicated that the objects shared features with The Cow, concluding these events, called Fast Blue Optical Transients (FBOTs), as representing a type of stellar explosion different from others.
Whilst FBOTs begin in the same way as certain supernovae and gamma-ray bursts, differences proceed in the aftermath of the initial explosion.
The explosions of "ordinary" supernova send spherical blast waves of material into interstellar space as well as a rotating disk of material that briefly forms around the neutron star or black hole left after the explosion.
This rotating disk and the narrow jets of gamma rays it produces are called an "engine" by astronomers.
FBOTs also have such an engine, but unlike in gamma-ray bursts, it is encased by thick material (likely shed by the star just before its explosion).
When the thick material near the star is struck by the blast wave, it causes the bright visible-light burst that is visible soon after the explosion. This intense blue brightness is what initially made these objects appear so unusual.
The discovery and observations of more 'blue beasts' is an exciting prospect for scientists, astronomers and space enthusiasts.