Astronomers recently captured a supermassive black hole sip down a star. It flared in exactly the same way as its smaller cousins do when the black holes have a snack. It just took longer and was a million times brighter.
Astronomers have seen the feeding habits of small, black holes in star mass for decades. These black holes often orbit other stars and occasionally live off of them. As material approaches the black hole, it compresses and forms a thin accretion disk. The heat from this growth generated a “soft” form of radiation, usually ultraviolet. However, when the material from the disk is thin out, a white-hot corona emits “hard” radiation in the form of X-rays.
The whole process is over and finished in a few days.
Supermassive black holes also eat up on their surrounding material, but astronomers had long thought that it would be impossible to observe this process play out in real time because it would take millions of years to build a flare and transition to a “Soft”
But then TDE AT2018fyk happened. It’s the name given to a particular flare seen by the All-Sky Automated Survey for Supernovae (ASASSN) in September 2018. It was a tidal eruption event that happens when a giant black hole tears an entire star to shred before eating the living.
A team of astronomers led by Dheeraj “DJ” Pasham, a researcher at MIT’s Kavli Institute for Astrophysics and Space Research, followed up with further observations of the event.
“In a tidal disturbance incident, everything is abrupt,” Pasham says. “You suddenly have a bit of gas being thrown at you and the black hole suddenly wakes up and it’s like ‘there’s so much food – let me just eat, eat, eat until it’s gone.’ So it experiences everything in a short period of time. It allows us to examine all these different accession phases that people have known in black holes in stellar mass. ”
Over the course of two years, astronomers were able to see the whole messy story unfold: an initial flash, the formation of an accession disk with is “soft” UV emission, the transition to “hard” X-ray emission, and a final disappearance.
“We’ve demonstrated that if you’ve seen a black hole, you’ve seen them all in a way,” Pasham says. “When you throw a ball of gas at them, they seem to do more or less the same thing. They are the same animal in terms of their growth. ”
“People have known that this cycle takes place in black holes in stellar mass, which is only about 10 solar masses. Now we see this in something 5 million times bigger, ”says Pasham.
Besides being really cool, these observations are only the second time that astronomers have captured the formation of a corona around a black hole.
“A corona is a very mysterious entity, and in the case of supermassive black holes, people have studied established corons, but do not know when or how they form,” says Pasham. “We have demonstrated that you can use tidal disturbance events to capture corona formation. I am excited to use these events in the future to find out what exactly is the corona. ”