Last summer, astronomers were astonished and puzzled by a mysterious, bright light, quite unlike anything they’d seen in the universe. It was 10 to 100 times brighter than a supernova, which were then the largest explosions ever seen by humans. And it flared up and largely died out in just 16 days, which, given that many light phenomena last for millions of years, is extraordinarily short.
Now, scientists believe that the explosion came from the precise moment a star collapsed to form either a black hole or a neutron star (which is an extremely small and dense star, typically around 30 km in radius, formed when a massive star collapses but doesn’t have enough gravitational pull to create a black hole.) “We know from theory that black holes and neutron stars form when a star dies, but we’ve never seen them right after they are born. Never,” Raffaella Margutti, astrophysicist at Northwestern University who led the research, said in a university press release.
Margutti’s team used hard X-rays (which were 10 times more powerful than normal X-rays) radio waves and gamma rays to study the explosion, which has been named AT2018cow, or “The Cow” (a nickname referencing the last three letters of its longer name, which comes from a randomized naming system used by Astronomer’s Telegram, a website where astronomers note interesting sightings.) Astrophysicists at ATLAS survey, an asteroid-impact early-warning system in Hawaii, first noticed The Cow in their telescope. Scientists around the world were then able to see the creation of this black hole or neutron star because far less material (or “ejecta mass,” in astronomy-lingo) was thrown out and swirling around the object than in a typical stellar explosion, according to their research published today (Jan. 10) in Astrophysical Journal. This meant the astronomers could look to the center of The Cow. “A ‘lightbulb’ was sitting deep inside the ejecta of the explosion,” Margutti said. “It would have been hard to see this in a normal stellar explosion. But The Cow had very little ejecta mass, which allowed us to view the central engine’s radiation directly.”
Astronomers were also able to The Cow because it was 200 million light years away—which, in universe scale, is just around the corner. “Two hundred million light years is close for us, by the way,” Margutti said. “This is the closest transient object [a relatively brief astronomical phenomenon, such as a supernova] of this kind that we have ever found.