Tour: NASA's Chandra Unveils Mysterious X-ray Objects

Scientists have discovered a new class of objects that are behaving unlike any they have seen before by using NASA’s Chandra X-ray Observatory. Astronomers suggest that these new objects may help solve not one, but two, long-standing questions in astrophysics.

The researchers found a total of 84 of what they call “hypersoft X-ray sources” in six different galaxies. They named them this because these mysterious objects give off unusually low-energy X-rays but intense levels of ultraviolet radiation.

The team discovered the hypersoft X-ray sources by looking for objects in the Chandra archive containing the lowest-energy X-rays. Two of the galaxies with these new objects are spirals, M31 and M101, and the other four are ellipticals. In addition to their different galactic homes, the hypersoft X-ray sources were found in both regions of active star formation and areas where there are older stars.

Given all of the clues the researchers gathered, they think the most likely explanation for these new sources involves a black hole, neutron star or white dwarf pulling material from a companion star. The material pulled from the companion star is heated up to produce X-rays before falling onto the white dwarf or neutron star, or into the black hole. Binary systems like this have been seen before but astronomers have never seen them behaving in this manner.

The discovery of this new class of sources suggests that large populations of binary systems with energetic ultraviolet radiation have previously been missed. Why were these hypersoft X-ray sources not found until now? In addition to the low-energy X-ray output, which is very difficult for X-ray telescopes to detect, the high-energy ultraviolet radiation is readily absorbed by helium and hydrogen gas that fills the space in between the stars, creating a “nearly impenetrable barrier” to look through.

By overcoming this observational obstacle, the researchers think this new class of objects may help explain the origin of Type Ia supernova explosions — the kind used to measure the accelerating expansion of the universe — as well as the stripping of electrons in gas in between galaxies. Whatever their role turns out to be, astronomers will be searching for more of these unusual objects and studying them with Chandra in the future.