A supermassive black hole is having a bit of an eating issue. It suddenly has so much material to feed on that it can’t swallow it quickly enough. This means the material is interacting with itself, emitting curious bursts of visible and ultraviolet light that then repeat in X-rays.
An international team of astronomers discovered that ASASSN-14li was emitting fluctuations of visible and UV photons. Around 32 days later, they found that the X-ray emissions from the hot gas was correlated to this time lag.
In a paper published in Astrophysical Journal Letters, the researchers suggest that this is due to self-interaction within the stream, and these interactions are being propagated closer to the black hole, where the gas is so hot it emits X-rays.
“In essence, this black hole has not had much to feed on for a while, and suddenly along comes an unlucky star full of matter,” lead author Dr Dheeraj Pasham of MIT said in a statement. “What we’re seeing is, this stellar material is not just continuously being fed onto the black hole, but it’s interacting with itself – stopping and going, stopping and going. This is telling us that the black hole is ‘choking’ on this sudden supply of stellar debris.”
ASASSN-14li is located 300 million light-years away and is known as a tidal disruption flare (TDF). Spotting one of these events is pretty difficult, so astronomers have assembled a network of telescopes (All Sky Automated Survey for SuperNovae or ASASSN) to check for TDFs over the full sky.
The way this particular supermassive black hole is feeding surprised scientists, who expected the accretion of material to be more continuous than they saw.
“For supermassive black holes steadily accreting, you wouldn’t expect this choking to happen," Pasham added. "The material around the black hole would be slowly rotating and losing some energy with each circular orbit. But that’s not what’s happening here. Because you have a lot of material falling onto the black hole, it’s interacting with itself, falling in again, and interacting again. If there are more events in the future, maybe we can see if this is what happens for other tidal disruption flares.”
The growth of supermassive black holes is related to the growth of galaxies as a whole, and the emissions from black holes can have widespread consequences. The intense radiation from black holes can be so powerful as to start hot winds that can quench star formation throughout a galaxy.