Hidden at the core of our Milky Way galaxy, the supermassive black hole Sagittarius A* or Sgr A*– a celestial behemoth far exceeding our Sun's mass by millions of times– has been historically characterized by its low luminosity compared to its counterparts in other galaxies. It seemed that this monstrous entity, situated over 25,000 light-years away from Earth, was on a cosmic hiatus, refraining from the active consumption of surrounding materials. However, recent data from NASA's IXPE (Imaging X-ray Polarimetry Explorer) telescope are painting a more dynamic picture, suggesting that the ancient sleeping giant woke up recently- about 200 years ago– to devour gas and other cosmic detritus it can reach.

This comes as Sgr A* became an object of scrutiny when earlier X-ray studies detected an unexpected luminosity around it. These studies revealed radiant gas clouds within its vicinity, a strange occurrence considering the usual dimness of most cosmic or "molecular" clouds. "We hypothesized that these vibrant molecular clouds could be an echo of a past X-ray flare, indicating that Sgr A* was not as dormant as we initially thought a few centuries back," said Frédéric Marin, an astronomer at the Astronomical Observatory of Strasbourg in France, and the leading voice in this groundbreaking research.

NASA's IXPE, an advanced telescope designed to measure the polarization of X-ray light, observed these mysteriously glowing molecular clouds in early 2022. Combining this data with additional information from NASA’s Chandra X-ray Observatory and archival observations from the European Space Agency’s XMM-Newton mission, astronomers were able to trace back the reflected X-ray signals to their origin. "Imagine the polarization angle as a compass, guiding us towards the original source of illumination," explained Riccardo Ferrazzoli, an astrophysicist at the Italian National Institute of Astrophysics in Rome. "Our compass pointed straight towards Sgr A*."

This meticulous examination of data suggested that the unusual radiance from the gas clouds was in fact a mirrored signal, a remnant of an intense, short-lived flare that was possibly the result of Sgr A* suddenly ingesting the surrounding cosmic materials. The team was able to estimate the initial flare's luminosity and duration, placing the event roughly around the beginning of the 19th century.

The research team, spearheaded by Steven Ehlert, IXPE project scientist at NASA's Marshall Space Flight Center, plans to refine these measurements by repeating the observations. Their future endeavors aim to provide more precise estimations about the flare's occurrence and its peak intensity and chart the three-dimensional distribution of the giant molecular clouds encircling the quiescent black hole.

It goes beyond mere astronomical curiosity

This ongoing study goes beyond mere astronomical curiosity; it seeks to shed light on the physical processes that could once again stir Sgr A* from its deep cosmic slumber. Ehlert noted, "Our exploration of the Milky Way's core is revealing how dynamic our galaxy's central black hole can be. It's evolving on a human timescale. As we uncover its history of activity and observe its changes over time, we are becoming better equipped to understand this cosmic giant."

NASA's IXPE mission, a collaboration with the Italian Space Agency and several international partners, is playing a critical role in advancing our understanding of these cosmic phenomena. The project continues to push the boundaries of our knowledge, bridging the vast distance between our planet and the dark heart of our galaxy.

Reference

●      LiveScience. (2023). Strange 'echo' from the Milky Way's central black hole reveals it briefly awoke 200 years ago. Available at- https://www.livescience.com/space/black-holes/strange-echo-from-the-milky-ways-central-black-hole-reveals-it-briefly-awoke-200-years-ago

●      Nasa TV. (2023). Milky Way’s Central Black Hole Woke Up 200 Years Ago, NASA’s IXPE Finds. Available at- https://www.nasa.gov/mission_pages/ixpe/feature/milky-way-s-central-black-hole-woke-up-200-years-ago-nasa-s-ixpe-finds