Three years ago, astronomers bore witness to a strange bright blue flare coming out of the spiral arm of a faraway galaxy 200 million light-years away. A survey in Hawaii was the first to see it, so it promptly sent out global alerts telling other telescopes to turn their giant eyes toward it.
And when they did that, they saw a dazzling flash 10 times brighter than a typical supernova before it faded over months, with leading theories speculating that the explosion may have created a subject like a black hole or neutron star.
Scientists called this mysterious stellar explosion 'the Cow', or AT2018cow, and now, they may finally have an explanation for what caused it in the first place.
A cosmic mystery
In a new study, researchers led by Dheeraj Pasham at the Massachusetts Institute of Technology took a closer look at the explosion to uncover its mysteries.
Based on previous research, "it still was not clear whether AT2018cow was a stellar explosion powered by a newborn compact object, or whether it was powered by shocks produced during a stellar explosion, interacting with the dense ambient medium," Pasham told Space.com. "Another hypothesis was that AT2018cow could have resulted from an intermediate-mass black hole weighing 10,000-100,000 solar masses ripping a star apart."
To uncover the mystery, the researchers looked at how the brightness of the x-rays from the source changed over time to see if there was a timeline where they varied regularly. After all, the explosion wasn't just a dazzling flash of light; it also included pulses and intense X-rays, with hundreds of millions of them being traced back to the same object. There was a rhythm to the pulses, too: They happened every 4.4 milliseconds throughout the course of 60 days.
Using the pulses as a starting point, scientists calculated that the source of the x-rays must be smaller than 621 miles (1,000 km) wide and have a mass of fewer than 800 suns. This would imply that it is a compact object, such as a small black hole or neutron star, and that the mystery flash occurred as a star died and gave birth to a baby black hole or neutron star. Then it ate the material around it, engulfing the star and generating powerful bursts of energy as it went.
"We have likely discovered the birth of a compact object in a supernova,” says Pasham, according to The Independent. "This happens in normal supernovae, but we haven’t seen it before because it’s such a messy process. We think this new evidence opens possibilities for finding baby black holes or baby neutron stars."