Using the Chandra X-ray space telescope, astronomers have discovered a new class of unusually low-energy X-ray objects that also emit high ultraviolet radiation but are not linked to any visible objects or star clusters at their locations.

You can read the research paper here [pdf]. The picture to the right is figure 2 from the paper, and shows the two types of these new X-ray objects (HSS and SSS) found in the spiral arms of the galaxy M101, also known as the Pinwheel Galaxy.

The researchers found a total of 84 of these “hypersoft X-ray sources” — so named because they give such low-energy X-rays — in the six different galaxies they searched, using data openly available to the public in the Chandra archive. Two of the galaxies are spirals, M31 (the Andromeda galaxy) and M101 (the Pinwheel galaxy), while the other four are ellipticals. They found hypersoft X-ray sources both in regions of active star formation and areas where there are older stars.

… It is unclear what types of objects are responsible for these low-energy X-rays and intense ultraviolet radiation. The team thinks they most likely involve 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. Such binary systems have been seen before, but not with such bright ultraviolet radiation and low-energy X-rays.

The discovery suggests that there may be large populations of binary systems with energetic ultraviolet radiation that have been undetected until now.

The objects were difficult to find because of their low X-ray output, which required this much more careful search to identify. And though the astronomers propose several theories as to what these objects are, there is presently not enough data to come to any firm conclusion. What the discovery does tell us however is that the evolution and death of stars is far more complex than posited by all present theories, all of which tend to simplify things far too much.