New astronomical findings from NASA indicate that the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), experienced a brief period of activity approximately 200 years ago. This revelation comes from observations made by the Imaging X-ray Polarimetry Explorer (IXPE), which detected X-ray emissions illuminating nearby molecular clouds.
For centuries, Sgr A* remained relatively dormant, showing no significant signs of activity. However, recent data suggests that this colossal black hole emitted a powerful X-ray outburst that lit up its surroundings before returning to a state of inactivity. The study detailing these findings was published in the journal Nature.
The unexpected brightness of large molecular clouds near the black hole was pivotal to this discovery. These clouds, which are typically cold and dark, were expected to emit only faint X-ray signals. Instead, the observations revealed intense emissions, leading researchers to theorize that these clouds might be echoing an ancient X-ray flash from the black hole.
“One possible explanation for the glowing of these giant molecular clouds is that they are reflecting a long-gone X-ray flash,” explained Frédéric Marin, an astronomer at the Strasbourg Astronomical Observatory and lead author of the study. “This suggests that our supermassive black hole was not completely inactive a few centuries ago.”
The IXPE is specifically designed to measure the polarization of X-ray light, allowing scientists to analyze the direction and intensity of the electric field within the light waves emitted by these clouds. Observations were conducted during February and March of 2022 and were combined with data from other observatories, including Chandra and XMM-Newton.
“The angle of polarization acts like a compass, pointing us toward the mysterious and vanished source of illumination,” said Riccardo Ferrazzoli, an astrophysicist at the National Institute for Astrophysics in Italy. “And what lies in that direction? None other than Sgr A*.”
The data confirmed that the light detected in the clouds was a reflection of a brief and intense eruption originating from the black hole or its vicinity, potentially caused by a sudden consumption of gas or cosmic dust.
According to the research team”s estimates, this outburst occurred roughly 200 Earth years ago, placing it in the early 19th century. In astronomical terms, this is a recent event, providing a unique opportunity to analyze how black holes alternate between periods of calm and bursts of activity.
Steven Ehlert, a scientist involved with the IXPE project, stated that the mission aims to repeat these observations to reduce uncertainties in their measurements and refine calculations regarding the intensity and duration of this event. These future observations will also assist in mapping the three-dimensional distribution of the molecular clouds surrounding the black hole.
“IXPE is playing a key role in helping us better understand the timescale over which the black hole at the center of our galaxy changes,” Ehlert remarked. “We know that such changes can occur in active galaxies and supermassive black holes on a human timescale. We are learning more about their behavior over time and their history of outbursts.”
The IXPE mission is a collaboration between NASA and the Italian Space Agency, involving scientists from twelve countries. Managed by NASA”s Marshall Space Flight Center, the spacecraft is operated by Ball Aerospace in Colorado alongside the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder.
This international collaboration allows scientists to gain new insights into the past of our galaxy. What was once a dark and silent region now reveals traces of intense recent activity. Sgr A*, the dormant heart of the Milky Way, had a fleeting awakening just two centuries ago, reminding us that even cosmic giants can stir in the blink of an eye.
