Sagittarius A*: A glimpse of the violent past of Milky Way's giant black hole

The X-ray emission shown here is from a process called fluorescence. Iron atoms in these clouds have been bombarded by X-rays, knocking out electrons close to the nucleus and causing electrons further out to fill the hole, emitting X-rays in the process. Other types of X-ray emission exist in this region but are not shown here, explaining the dark areas.

X-ray Image of Sagittarius A* [Credit: NASA/CXC/APC/Universite
Paris Diderot/M.Clavel et al]

This is the first time that astronomers have seen both increasing and decreasing X-ray emission in the same structures. Because the change in X-rays lasts for only two years in one region and over ten years in others, this new study indicates that at least two separate flares were responsible for the light echoes observed from Sgr A*.

There are several possible causes of the flares: a short-lived jet produced by the partial disruption of a star by Sgr A*; the ripping apart of a planet by Sgr A*; the collection by Sgr A* of debris from close encounters between two stars; and an increase in the consumption of material by Sgr A* because of clumps in the gas ejected by massive stars orbiting Sgr A*. Further studies of the variations are needed to decide between these options.

The researchers also examined the possibility that a magnetar - a neutron star with a very strong magnetic field - recently discovered near Sgr A* might be responsible for these variations. However, this would require an outburst that is much brighter than the brightest magnetar flare ever observed.

A paper describing these results has been published in the October 2013 issue of the journal Astronomy and Astrophysics and is available online.

Source: Chandra X-ray Center [October 24, 2013]