Two new sources of X-ray flares — explosive bursts of X-rays — in galaxies near the Milky Way have been found by international scientists but what exactly caused the flares remains a mystery. The researchers say that although they don't know what the sources of the X-rays are, they are unlike any known object in the Milky Way and seem to be located in old star populations.
Prior to this study, two very brief X-ray flares with high luminosity were detected near the galaxy NGC 4697, in 2003 and 2007.
Jimmy Irwin and colleagues examined archival data from Chandra X-ray observations for 70 galaxies near the Milky Way to find similar flares. They investigated several thousand X-ray point sources and identified just two sources of similar flares. One of the sources flared once, the other flared five times.
The time it took the flares to rise was less than one minute each time, and the flares decayed over the course of about one hour. Unlike other astronomical objects that produce flares, such as those associated with gamma ray bursts or supernovae, these sources do not self-destruct in the process of flaring.
The discovery suggests that the sources, when not flaring, appear to be accreting in globular clusters or ultracompact dwarf galaxies near elliptical galaxies.