The Milky Way’s supermassive black hole just produced a brilliant, mysterious flash

The black hole often flickers, but outbursts are incredibly rare. A bright flash indicating a burst of activity was observed as scientists trained the lens on the black hole before it dimmed over the course of a couple of hours. While the black hole itself, by definition, does not emit light or detectable radiation, it is nonetheless surrounded by matter that may become excited by activity within the black hole, emitting electromagnetic waves detectable by Earth radio telescopes. "The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sagittarius A* that bright".

S0-2 has been spotted a mere 17 light-hours away from the center as recently as past year, and it's possible that the star's close relationship with the black hole has led to an increase in gas being swallowed up by it, which may have led to a burst of radiation visible using infrared.

Do's team's findings have been published in The Astrophysical Journal Letters, though work is still underway to figure out why, exactly, Sgr A*'s output changed so significantly.

Scientists have been watching Sagittarius A* for decades, but no one was sure what to make of it for much of that time; it was just a strong X-ray source deep in the Milky Way. It's possible a large volume of matter fell into the black hole's gravity well, and that caused the flash.

The first frame - taken right at the beginning of the observation - is the brightest, which means Sgr A* could have been even brighter before they started observing, Do said. As ScienceAlert reports, the research team has a couple of possibilities in mind. There's also a gas cloud called G2 that swing around Sagittarius A* in 2014. That's S0-2, a star on a long, looping, 16-year elliptical orbit around Sgr A*. It made its closest approach yet a year ago, coming within 17 light hours of the event horizon.

"One of the possibilities", Do told ScienceAlert, "is that the star S0-2, when it passed close to the black hole a year ago, changed the way gas flows into the black hole, and so more gas is falling on it, leading it to become more variable". "Additional multi-wavelength observations will be necessary to both monitor Sagittarius A* for potential state changes and to constrain the physical processes responsible for its current variability". Keck will be providing data for another few weeks, Do says, though after that point the Galactic center will not be at the right angle for observation again until 2020.

Do told ScienceAlert they are now waiting for data from other telescopes, including NASA's Spitzer and Chandra, to better understand what might have happened with Sagittarius A*.