Two years ago evidence of a major cosmic eruption reached Earth in the form of a light blue lightning bolt. It was called “the cow” and looked like a supernova – the dramatic death of a star – but it happened even faster than the well-known star death. Now a team of astronomers believe they have reduced the list of cosmic suspects to just two: the X-rays were emitted either by a small black hole or a neutron star. The team’s results are released today in natural astronomy.
“The amount of energy was orders of magnitude higher than that of the typical core collapse supernova,” said Dheeraj Pasham, an astronomer at MIT and lead author of the new paper, in an MIT release. “The question was, what could this additional source of energy produce?”
First, the team simulated noises from the object about 50,000 times, Pasham Gizmodo said in an email. They found that there was only a 0.02% chance that the signal they saw was a diversionary maneuver. The impulses came from an object called AT2018cow – or the cow for short – located 200 million light years from Earth. This nickname was just a coincidence of the astronomical naming; There is a similar object called the koala. Both objects are Fast Blue Optical Transients (FBOT), a rare class of objects known to look like supernovae but are more fleeting and 100 times brighter.
While the cow’s identity remains unknown, the research team that examined the object determined that it was either a black hole or a neutron star based on the frequency of its X-ray pulses, which occurred every 4.4 over a 60 day period Milliseconds occurred.
The frequency of the pulses gave the researchers a sense of its size – no more than about 998 km in diameter, with a mass of no more than 850 suns. But since the diameter of the sun is about 1,392,083 km, this makes the cow extremely compact.
Black holes and neutron stars are the densest known objects in the universe, and both occur at the end of the stellar life cycle. Black holes are those enigmatic objects with gravitational fields so strong that even light cannot escape them, while neutron stars are dead stars with so strong gravity that electrons collapse on protons, effectively making a star entirely made up of neutrons.
Pasham told Gizmodo that the object rotates about 224 times per second. (The cow is a pulsar, which means that it periodically flashes a signal that can only be seen on Earth when it is pointed in our direction. Since the cow’s X-ray flash frequency was 224 Hz, the researchers know that it is turns so fast.).
If the researchers were able to determine exactly how dizzyingly fast the object was rotating, they would be able to determine with certainty what it is. “I think the cow is just the beginning of what’s to come,” said Pasham. “More such objects would open a new window into these extreme explosions.”
Whatever the object, astronomers saw its birth in 2018. As they examine more data from the cow and similar objects, their identity may become less mysterious.
Publisher’s Note: The release dates in this article are for the United States but will be updated with local Australian dates as we know more.