The supermassive black hole in the center of our Milky Way Galaxy, known as Sagittarius A* (or Sgr A*), may seem quiet, but it does have its moments of activity. Sometimes, it devours a blob of molecular gas or even a star, which can lead to x-ray flares being emitted into space.
Located at a distance of 26,000 light-years from Earth, Sgr A* is the closest supermassive black hole to us. However, studying its nearby environment is challenging due to its intense gravitational pull, which distorts the view of surrounding objects. Despite these difficulties, astronomers have found a way to observe the effects of the black hole’s flares on nearby molecular clouds.
Recently, researchers from Michigan State University, Grace Sanger-Johnson, and Jack Uteg, delved into the study of these flares and their light echoes. By examining the echoes of past flares, they were able to uncover evidence of Sgr A*’s activity in the distant past when it consumed material. The x-ray emissions from these events traveled for centuries before bouncing off a nearby molecular cloud, creating a light echo that eventually reached Earth after approximately 26,000 years.
Through their research, Sanger-Johnson and Uteg shed light on the historical activity of Sgr A* and provided insights into the frequency of these outbursts. They analyzed data from the NuSTAR mission, which focuses on high-energy x-ray and gamma-ray emissions, and identified nine more outbursts in addition to the previously known ones.
The study of these flares not only allows astronomers to understand the immediate environment around the black hole but also provides valuable information about the physical conditions within this extreme environment. By compiling a database of Sgr A* flares, researchers aim to gain further insights into the properties of these events.
Uteg’s work involved tracking the echoes of past flares by analyzing data from a giant molecular cloud called “the Bridge.” The observation of increased X-ray brightness in the Bridge led researchers to infer that it was a delayed reflection of past x-ray outbursts from Sgr A*. This information helped astronomers estimate the brightness of Sgr A* during past outbursts and understand the impact of these events on the surrounding environment.
The findings of these studies offer a new perspective on observing black holes and provide valuable information about the frequency and effects of flares from Sgr A*. By continuing to study these phenomena, researchers hope to unravel more mysteries surrounding the center of our Milky Way Galaxy.