Astronomers who have been observing the black hole at the center of the Milky Way galaxy noticed something extraordinary they have not seen over the past 20 years they have been watching the object.

The black hole Sagittarius A* is usually very dim. Astronomers observe it by looking at the matter around it. When the black hole is more active than usual.

The black hole is usually on the quiet side despite it being 4 million times more massive than the sun. It may be a bright X-ray radio source because of the heating of matter in its accretion disk, but it is not active enough to be bright across most of the electromagnetic spectrum.

This, however, changed in May this year when astronomers using the Keck telescopes on Mauna Kea in Hawaii spotted an unusual pulse from the black hole.

Astronomers initially thought the flash came from a star in the same part of the sky, but it eventually became apparent that the source was Sagittarius A*. At some point, the black hole was 75 times brighter than usual in infrared.

Tuan Do, an astronomer at the University of California, Los Angeles, said the black hole was even brighter before they started observing.

Astronomers are not yet certain what caused this extraordinarily bright flaring, but they have some theories.

While the black hole itself do not emit radiation that can be detected on Earth, objects near it that are being torn to shreds due to gravity would. A large volume of matter may have fallen into the black hole’ gravity, which may have caused the flash.

The researchers think of two possibilities: the S0-2 star near the black hole made a close approach to the event horizon and a part of it may have been pulled away during its passage.

A gas cloud called G2 also swung around Sagittarius A* in 2014. Astronomers did not observe cosmic fireworks at the time, but the observed brightness could be a delayed reaction. 

“Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion-flow as a result of the star S0-2's closest passage to the black hole in 2018 or from a delayed reaction to the approach of the dusty object G2 in 2014,” the researchers wrote in their study, which will be published by the Astrophysical Journal Letters.