More Transients

Hercules climbs into good view in the east and northeast a couple of hours after sunset. His torso is outlined by a lopsided square of stars known as the Keystone.
The constellation produced a big bang that was seen last June. It was cataloged as AT2018cow, and nicknamed “the Cow.”
The Cow was a fast-evolving luminous transient — a class of objects first seen only in the last few years. They flare up in a few days — far quicker than a typical supernova, which is a huge stellar explosion. And astronomers are having a tough time deciding what powers them.
A transient discovered in 2015, by the Kepler space telescope, flared up in just two days. Some astronomers suggested it was a supernova, but an odd one: The blast ran into gas around the star, producing a brilliant shock wave.
A couple of years later, another team produced another explanation for these transients: the merger of two stellar corpses known as white dwarfs.
The Cow produced even more possible explanations. One says that a