The supermassive black hole at the center of our galaxy has become unexpectedly active, with astronomers generally puzzled as to why Sagittarius A* has suddenly lit up with extreme brightness. Almost 26,000 light years from Earth, Sagittarius A* – or Sgr A* – is typically fairly restrained as supermassive black holes go, but this past summer that has all been flipped.
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. While the supermassive black hole itself isn’t visible, its so-called electromagnetic counterpart can be tracked.
While there’s always some variation in brightness as to the amount of near-infrared energy that emits, things have shifted to a whole new scale in 2019. Observations from the Keck Telescope have shown its been a record year for emissions, with one two hour period seeing Sgr A* getting 75x brighter than normal. Double brightness for extended periods has also been observed.
“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,” astronomer Tuan Do from the University of California Los Angeles told ScienceAlert about the observations. “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.”
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. In a timelapse from the May 13 observations, the black hole’s unexpected activity in the infrared is clear.
Luckily, there are plenty of sources for extra data to help fathom the cause of the change. 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. However four other telescopes – including Spitzer, Swift, Chanrdra, and ALMA – have been making observations over the summer, with their data still to be released.
While a black hole itself does not release light or any other energy, the periphery does as the immense forces involved grind on what’s in the accretion disk. That’s the mass of materials – including gases and dusts – that are drawn to the black hole but don’t make it past the event horizon. Passing stars, orbiting around the black hole because of its incredible gravity, can end up donating their material to the disk as they graze by those forces, and it’s theorized that this Sgr A* activity is because of an extra-large meal from one such pass.