Black holes are regions of spacetime displaying gravitational acceleration so strong that nothing – even light – can escape. The supermassive black hole siting at the Milky Way’s core normally relatively predictable as it shapes the orbits of nearby stars. But in May, the area just outside the black hole’s event horizon – the threshold of no return for anything falling into the hole – suddenly flared with unprecedented intensity.
This was the third such outburst this year alone.
While black holes are, by definition, invisible, gas and dust sucked in by their enormous gravity are accelerated to extreme velocities, generating enormous heat that produces visible high-energy radiation before the material moves past the hole’s event horizon.
Andrea Ghez, University of California, Los Angeles (UCLA) professor of physics and astronomy and a co-senior author of a paper describing the incredible incidents, said: “We have never seen anything like this in the 24 years we have studied the supermassive black hole.
“It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.”
The UCLA astronomers analysed more than 13,000 observations of the black hole, known as Sagittarius A* (Sgr A*), that were captured since 2003 by the W.M. Keck Observatory in Hawaii and the European Southern Observatory’s Very Large Telescope in Chile.
And the 13 May event was twice as bright as any previous observation.
Combined with the two outbursts observer earlier in the year, astronomers now believe a feeding frenzy of sorts might be underway.
Tuan Do, the study’s lead author, said: “The first image I saw that night, the black hole was so bright I initially mistook it for the star S0-2, because I had never seen Sagittarius A* that bright.
“But it quickly became clear the source had to be the black hole, which was really exciting.”
A star called S0-2 made a close pass by Sgr A* last summer and it is possible the black hole’s enormous gravity tore off a vast amount of gas that is only now being sucked in.
Another possibility is an object called G2, which is likely a pair of binary stars, suffered a similar fate during a close flyby in 2014.
Mark Morris, UCLA professor of physics and astronomy and the paper’s co-senior author, said: “The big question is whether the black hole is entering a new phase, for example if the spigot has been turned up and the rate of gas falling down the black hole ‘drain’ has increased for an extended period, or whether we have just seen the fireworks from a few unusual blobs of gas falling in.
More observations are needed to pin down the nature of Sgr A*’s feast.
Professor Ghez added: “We want to know how black holes grow and affect the evolution of galaxies and the universe.
“We want to know why the supermassive hole gets brighter and how it gets brighter.”