– A mysterious flash of X-rays has been discovered by NASA’s Chandra X-ray Observatory in the deepest X-ray image ever obtained.
Astronomers believe this source likely originates from some sort of destructive event, but may be of a variety that scientists have never seen before.
The X-ray source, located in a region of the sky known as the Chandra Deep Field-South (CDF-S) has remarkable properties.
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. After about a day, the source had faded completely below the sensitivity of Chandra.
Astronomers who have analyzed data from the Hubble and Spitzer Space Telescopes, have been able to determine that the event likely came from a faint, small galaxy about 10.7 billion light years from Earth.
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’ve been struggling to understand its origin,” said Franz Bauer of the Pontifical Catholic University of Chile in Santiago, Chile. “It’s like we have a jigsaw puzzle but we don’t have all of the pieces.”
Two of the three main possibilities to explain the X-ray source invoke gamma-ray burst (GRB) events.
Possible explanations for the CDF-S X-ray source, according to the researchers, are a GRB that is not pointed toward 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,” said co-author Ezequiel Treister, also of the Pontifical Catholic University, “but then again, we’ve rarely if ever seen any of the proposed possibilities in actual data, so we don’t understand them well at all.”
The mysterious X-ray source was not seen at any other time during the two and a half months of exposure time Chandra has observed the CDF-S region, which has been spread out over the past 17 years.
Moreover, no similar events have yet to be found in Chandra observations of other parts of the sky.
A paper describing this result appears in the June 2017 issue of the Monthly Notices of the Royal Astronomical Society and is available online.