Black holes have always been of interest to astronomers, but their nature remains a mystery. One of the most studied black holes, Sagittarius A* (Sgr A*), is located in the center of our Milky Way galaxy and, until recently, was thought to be inactive. However, a new study published in Nature shows that Sgr A* is not as dormant as previously thought.
Researchers from various countries discovered that about 200 years ago, the black hole woke up to devour several nearby space objects and then fell asleep again. NASA’s IXPE space observatory recorded X-ray echoes of this powerful burst of activity. As the researchers note, Sgr A* has always been viewed as an inactive black hole.
The supermassive Sagittarius A* black hole is four million times more massive than the Sun. It is 27,000 light-years from Earth, at the center of the Milky Way spiral. Last year, astronomers published the first-ever image of a black hole – or rather, the glowing ring of gas surrounding its blackness.
According to Frederic Marin, a researcher at the Strasbourg Astronomical Observatory in France and the first author of the study, most supermassive black holes at the center of their galaxies go into hibernation after absorbing all nearby matter. However, Sgr A* came out of hibernation and absorbed the gas and dust that were unlucky enough to be within its reach. His frenzy lasted from a few months to a year before he went back into hibernation.
When the black hole was active, it was at least a million times brighter than it is today. Its awakening was noticeable because nearby galactic molecular clouds began to emit significantly more X-ray light. The burst of X-rays was “as if a lone firefly hidden in a forest suddenly became as bright as the sun,” the French research agency CNRS said in a statement.
Astronomers using NASA’s IXPE (Imaging X-ray Polarimetry Explorer) space observatory tracked the X-ray beam and found it pointed directly at Sgr A*. The gravitational pull of black holes is so strong that nothing can escape, including light. But when matter is sucked beyond the final boundary of a black hole, known as the event horizon, it releases enormous amounts of heat and light before disappearing into darkness.
What exactly caused Sgr A* to briefly emerge from its dormant state remains unclear. Maybe a star or a cloud of gas and dust got too close? Astronomers hope that further observations from the IXPE observatory will help them better understand what happened.