A mysterious flash of X-rays has been discovered by NASA’s Chandra Observatory in the deepest X-ray image ever obtained. This source likely comes from some sort of destructive event, but may be of a variety that scientists have never seen before, NASA said. The X-ray source, located in a region of the sky known as the Chandra Deep Field-South (CDF-S), has remarkable properties, it said.
Prior to October 2014, this source was not detected in X-rays, but then it erupted and became at least a factor of 1,000 brighter in a few hours. The event likely came from a faint, small galaxy about 10.7 billion light years from Earth, NASA said. For a few minutes, the X-ray source produced a thousand times more energy than all the stars in this galaxy. “Ever since discovering this source, we have been struggling to understand its origin,” said Franz Bauer of the Pontifical Catholic University of Chile. “It is like we have a jigsaw puzzle but we do not have all of the pieces,” said Bauer.
Two of the three main possibilities to explain the X-ray source invoke gamma-ray burst (GRB) events. GRBs are jetted explosions triggered either by the collapse of a massive star or by the merger of a neutron star with another neutron star or a black hole. If the jet is pointing towards the Earth, a burst of gamma rays is detected. As the jet expands, it loses energy and produces weaker, more isotropic radiation at X-ray and other wavelengths.
Possible explanations for the CDF-S X-ray source, according to the researchers, are a GRB that is not pointed towards Earth, or a GRB that lies beyond the small galaxy. A third possibility is that a medium-sized black hole shredded a white dwarf star. “None of these ideas fits the data perfectly, but then again, we have rarely if ever seen any of the proposed possibilities in actual data, so we do not understand them well at all,” said Ezequiel Treister, also of the Pontifical Catholic University.
The CDF-S source is likely associated with the destruction of a neutron star, white dwarf, or massive star, and is roughly 100,000 times more luminous in X-rays. It is also located in a much smaller and younger host galaxy, and is only detected during a single, several-hour burst. The research appears in the journal Monthly Notices of the Royal Astronomical Society.