The supermassive black hole at the heart of the Milky Way is getting hungrier

Rendering of a star called S0-2 orbiting the supermassive black hole at the center of the Milky Way. It did not fall in, but its close approach could be one reason for the black hole’s growing appetite. Artist’s rendering by Nicolle Fuller/National Science Foundation

Last month, we learned that the supermassive black hole at the center of our galaxy was flaring, although no one was sure why. Now, astronomers from the University of California, Los Angeles (UCLA) have revealed more about what they think may be driving this unprecedented event.

Lying at the heart of the Milky Way, the Sagittarius A* or Sgr A* black hole is typically a relatively gentle giant. But when astronomers analyzed 13,000 observations of it from 133 nights since 2003, they found that on May 13 of this year the matter around the black hole glowed twice as brightly as usual. The same bright flaring was observed on two other nights this year as well. This indicates the black hole is consuming much more dust and gas on these nights than is usual.

“We have never seen anything like this in the 24 years we have studied the supermassive black hole,” Andrea Ghez, professor of physics and astronomy at UCLA and a co-author of the research, said in a statement. “It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.”

The first issue to address is whether this was a singular event or whether it indicates a dramatic change in Sgr A* over the long term. “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,” Mark Morris, another co-author of the paper, explained in the same statement.

Some of these unusual blobs of gas could have come from the star S0-2, which recently passed close to the black hole but did not get sucked in. As the star passed by during summer last year, it could have lost a large portion of gas which took some time to reach Sgr A* before falling in and causing the flares. Alternatively, the black hole could have sucked the outer layer off another object, called G2, which passed close by in 2014. Yet another theory is that large asteroids were drawn into the black hole and caused the flares.

In any case, the scientists reassured the public that Sgr A* may be hungry, but it is no danger to humanity. It is located 26,000 light-years away and would have to be 10 billion times brighter than the highest detected levels to affect us here on Earth.

The findings are published in Astrophysical Journal Letters.