Astronomers Spot Mysterious Flash From Our Galaxy's Supermassive Black Hole

Rodiano Bonacci
Agosto 13, 2019

The supermassive black hole at the heart of the Milky Way, Sagittarius A*, is relatively quiet.

In news that reads like the beginning of a dire science fiction novel Sagittarius A*, the supermassive black hole at the centre of our galaxy, has emitted a large burst of infrared radiation brighter than anything ever produced by that black hole.

An attempt to prove Einstein's hallmark theory of gravity revealed something even freakier: an unprecedented flash from the black hole at the centre of our galaxy. But when the surroundings of a black hole flare that brightly, it's a sign something may have gotten close enough to be grabbed by its gravity.

Sagittarius A*-the Milky Way's central black hole-is normally quite subdued, with low levels of activity recorded over years.

The galaxy, Holm 15A, sits around 700 million light-years away, making it somewhat hard to study in detail, but what scientists know for sure is that the black hole in its heart is the largest ever discovered. A team of researchers used the data gathered by the WM Keck Observatory in Hawaii over four nights in May.

While a black hole itself does not release light or any other energy, the periphery does as the huge forces involved grind on what's in the accretion disk. That's the brightest we've ever seen Sgr A* in near-infrared wavelengths. Black holes themselves don't emit any radiation that can be detected by our current instruments, but the stuff nearby does when the black hole's gravitational forces generate enormous friction, in turn producing radiation. It's thought to be at least twice as large as the previous largest black hole detected by scientists. In fact, researchers believe the black hole in Holm 15A is at least 10,000 times as massive as our home galaxy's black hole. There is a possibility this is a delayed reaction to that event.

But - have a look at the timelapse again. They said the increase in brightness could suggest a change in activity at the supermassive black hole.

According to the researchers, the sudden flash is as mysterious as it is anomalous, but they hypothesize that it could be spurred by the close approach of a star called S0-2. It made its closest approach yet a year ago, coming within 17 light hours of the event horizon.

Scientists have been observing Sgr A* for years now, most recently including data from the Event Horizon Telescope and the High-resolution Airborne Wideband Camera-Plus.

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

Currently, scientists are gathering as much information as they can. However four other telescopes - including Spitzer, Swift, Chanrdra, and ALMA - have been making observations over the summer, with their data still to be released.

There are only a few weeks left before the black hole will be visible from the Keck Observatory.

The paper has been accepted into The Astrophysical Journal Letters, and is available on arXiv.

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