The giant blackhole at the core of the Milky Way became 75 times brighter in just 2 hours, and scientists have no idea why

Compared to an active nucleus which spews out light and heat, Sagittarius A*, the supermassive black hole at the heart of the Milky Way, is usually quite calm, displaying minimal fluctuations in its brightness.

On May 13 scientists observing with the Keck Telescope on the summit of Mauna Kea in Hawaii noticed the black hole growing 75 times brighter in the near-infrared band of the light spectrum. Sgr A* is the closest black hole to us, located just 26,000 light-years from Earth.

A time lapse was captured showing the scene condensed down into a few seconds:

Tuan Do, a UCLA astronomer told ScienceAlert that he didn’t even know what he was looking at initially.

He explained:

I was pretty surprised at first and then very excited.

The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sgr A* that bright. Over the next few frames, though, it was clear the source was variable and had to be the black hole. I knew almost right away there was probably something interesting going on with the black hole.

In a forthcoming study set to be published in The Astrophysical Journal Letters, Do explains the Milky Way’s supermassive black hole ‘reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths’.

The scientists are still unsure about what exactly caused the black hole to suddenly light up but data is being gathered in an attempt to figure it out.

According to ScienceAlert, black holes themselves don’t emit radiation which we can detect but the surroundings do when the black hole’s gravitational forces generate immense friction, which produces radiation.

The radiation translates as brightness when we view it with a telescope so when the surroundings of a black hole flare like they did on May 13 it’s a sign something may have come close enough to be grabbed by its gravity.

One possibility is an object thought to be a gas cloud, known as G2, which approached within 36 light-hours of Sagittarius A* in 2014. If it is a gas cloud the proximity should have torn the object apart, but nothing happened. However, scientists have suggested the recent sudden brightness was a delayed reaction.

Keck/UCLA Galactic Center Group

Another possibility is the star S0-2, which is on a 16-year elliptical orbit around Sgr A* and last year made its closest approach.

Do said:

One of the possibilities is that the star S0-2, when it passed close to the black hole last year, changed the way gas flows into the black hole and so more gas is falling on it, leading it to become more variable.

Astronomers will continue to observe the supermassive black hole in the coming weeks to gather more data and the team are currently awaiting results from other telescopes which have been observing Sgr A* in the last few months.