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.
While it is normal for the supermassive black hole to fluctuate slightly in brightness, the researchers found Sagittarius A*-which is four million times the mass of the sun-had gotten 75 times brighter than normal.
"It was probably even brighter before we started observing that night!" 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.
S0-2 has been spotted a mere 17 light-hours away from the center as recently as a year ago, 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.
But what? That's what astronomers are on a mission to find out.
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. It's under constant observation with instruments like the WM Keck Observatory in Hawaii used by the UCLA team. The odd brightening took place on May 13, and the team managed to capture it in a timelapse, two hours condensed down to a few seconds. 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 vast friction, in turn producing radiation. Another cause could be a change to its accretion state-how the black hole is drawing matter inwards. One is a large gas cloud that was recently observed just a few dozen light-hours away from the black hole which may have been drawn in ripped apart, and the other is a star known as S0-2.
The team is busily gathering data to try and narrow it down, but there are two immediate possibilities. If it was a gas cloud, this proximity should have torn it to shreds, and parts of it devoured by the black hole - yet nothing happened. There were no cosmic fireworks at the time, but we could be seeing a delayed reaction. See that bright dot at around 11 o'clock from the black hole? First, the aforementioned S0-2, which is in a long 16-year orbit of Sagittarius A*. Last year, it made its closest approach, coming within 17 light-hours of the black hole.
The only way to find out is having more data. They are now being collected, across a larger range of wavelengths. 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.