The Cow: a mysterious explosion in space
On Earth, more than 350 thousand babies are born each day. If you think that is a lot, take a look at our Universe. In space, more than 100 million stars are born each day. But recently, something mysterious was born, something that astronomers have never seen before.
The new-born was an extremely bright explosion. When astronomers discovered it, they were baffled. Imagine how excited you must be when you find out something new in the Universe! They started looking at it with telescopes from all over the world, including ALMA. But to this day, they still don’t know what it is.
To find out what the new object is, it sometimes helps to first figure out what it is not. The strange explosion looked much, much brighter than the explosive death of a star, a ‘normal’ supernova. So, this was not the explanation. Was it a hypernova, astronomers wondered? Hypernovas are even more extreme than supernovas. They are caused by the death of a more massive object, such as a black hole or an extremely massive star. But hypernovas only last seconds, and this peculiar explosion lasted for weeks. So, this couldn’t be the explanation either.
The astronomers used their imagination to come up with ideas to explain the explosion. They all agreed that there must be a powerful engine in the center of this object. This engine could be a rapidly-rotating dead star with a strong magnetic field, a so-called magnetar. Or the motor could be a black hole that was feeding itself from surrounding material.
The magnetar or the black hole could have been born right after a supernova explosion. This would be very exciting because such a birth has never been seen before! Astronomers can’t yet say which explanation is the right one. To do that, they have to study this object in more detail. They are also using ALMA to try and find other objects that look similar. Hopefully, we will know more soon!
The explosion is called AT2018cow, also known as ‘The Cow.’ This has nothing to do with cows—astronomers have to use an alphabetic method to name the objects they find. This object happened to get the letters ‘c o w’. The Cow explosion occurred in a galaxy 200 million light-years from Earth and was 10-100 times brighter than a typical supernova.
The Cow was first detected on 16 June 2018 with the ATLAS telescope in Hawai’i. The mysterious explosion then immediately got the attention of astronomers worldwide, and more telescopes were pointed at that object. Anna Ho from Caltech led a team using ALMA, among other telescopes, in Chile. Rafaella Margutti from Northwestern University led a team that used telescopes ranging from gamma rays to radio waves, including the Very Large Array, to study the object. The astronomers presented their findings of the object at the American Astronomical Society’s meeting in Seattle, Washington, in January 2019.