Whenever the monster at the center of the Milky Way feasts on material surrounding the supermassive black hole, it flares up. Astronomers have detected many flares from previously unobserved matter. Scientists are also investigating changes in the brightness of a molecular cloud that preserves evidence of past explosions by the Milky Way’s central supermassive black hole.
A description of a black hole. (Image credit: NASA SVS/GSFC).
New Delhi: Sagittarius A* or Sgr A* is the name of the supermassive black hole occupying the center of the Milky Way galaxy. All massive galaxies are now believed to harbor such supermassive black holes. However, Sgr A* is not a turbulent feeder like some other known supermassive black holes, and is not active. The more active the black hole, the brighter the accretion disk of matter. Whenever a supermassive black hole feasts, there are flares from surrounding objects.
An infrared view of the Milky Way and its bright black hole. (Image credit: NuSTAR/NASA).
Astronomers have now identified nine previously unobserved flares from Sgr A*. These bursts were observed in historical data collected by NASA’s Atomic Spectroscopic Telescope Array or Nustar X-ray telescope. These dramatic bursts of high-energy light have not been observed before. Each newly discovered event allows scientists to better understand the supermassive black hole at the center of the Milky Way and the intense environment surrounding it.
Echoes of a supermassive black hole
Near Sgr A* is a giant cloud of molecular gas known as 'The Bridge’. This cloud does not produce its own X-ray light. However, astronomers have picked up photons emanating from the bridge that could delay X-ray reflections from past bursts from Sgr A*. By measuring Sgr A*’s echoes from the bridge, scientists are creating a timeline of past activity by Sgr A*.
Scientists have been able to determine that 200 years ago, Sgr A* was five times brighter than it appears today, suggesting that it was eating up surrounding material more vigorously. Researcher Shuo Zhang He says, “This is the first time we have produced a 24-year timescale of variability for a molecular cloud surrounding our supermassive black hole, which has reached its peak X-ray luminosity. This allows us to tell the past activity of Sgr A* back to about 200 years ago. Our research team at MSU will continue this 'astroarchaeology game’ to further unravel the mysteries of the Milky Way’s core.