MIT study says all black holes undergo similar accretion cycles

MIT researchers have been conducting a study into black holes of various sizes. On September 9, 2018, a fortuitous event occurred when astronomers spied a flash of light from a galaxy about 860 million light-years away. The source of the flash of light was a supermassive black hole approximately 50 times the mass of the sun that was normally very quiet.

The flash of light was created when the black hole consumed a star passing nearby in a rare event known as a tidal disruption event. As that stellar debris fell towards the black hole, an enormous amount of energy in the form of visible light was released. Researchers from MIT and other organizations use multiple telescopes to watch the events unfold. They observed something interesting in that the supermassive black hole exhibited properties that were similar to those of much smaller stellar-massive black holes.

The study results suggest that accretion, which is the way black holes evolve as they consume material, is independent of their size. Study author Dheeraj Pasham says that the team has demonstrated if you have seen one black hole, you've seen them all in a sense. Researchers note that when small stellar-mass black holes about ten times the sun's mass emit a burst of light, it's typically in response to an influx of material from a companion star.

The outburst of radiation sets off a specific evolution of the region around the black hole transforming it into a "soft" phase dominated by an accretion disk as stellar material is pulled into the black hole. As the influx of material declines, the black hole transitions into a "hard" phase where a white-hot corona takes over. Eventually, the black hole settles into a steady quiescence with the entire cycle lasting a few weeks to months.

For supermassive black holes, scientists believed the process would take too long to capture entirely because they typically feed slowly on gas in the galaxy's central regions. In supermassive black holes, the process normally happens on timescales of thousands of years. The entire process speeds up when the black hole experiences a sudden and massive influx of material, such as during a tidal disruption event when a star is close enough to the black hole that it can be tidally ripped to shreds. The star in this instance that was tidally disrupted was about the size of the sun generating an accretion disk about 12 billion kilometers wide.