NASA's Chandra Telescope Finds a Bizarre New Class of Cosmic Objects

Using data from NASA's Chandra X-ray Observatory, astronomers have identified a new class of cosmic objects that behaves unlike anything cataloged before. The discovery, led by Mustafa Muhibullah of the University of Alabama, is described in a paper published in the journal Nature Astronomy.

The team found 84 of these objects, which they named "hypersoft X-ray sources" because they give off unusually low-energy X-rays. The objects turned up in six galaxies, including the spiral galaxies M31 (the Andromeda galaxy) and M101 (the Pinwheel galaxy), plus four elliptical galaxies. They appeared in both regions of active star formation and areas containing older stars. Researchers found them by searching through data already public in the Chandra archive, spotting objects that showed up in the lowest-energy X-ray images but disappeared at higher energies.

Because low-energy X-rays sit next to ultraviolet light on the electromagnetic spectrum, the researchers concluded these sources also give off large amounts of energetic ultraviolet radiation, a combination not seen before. The team thinks the objects are most likely binary systems in which a black hole, neutron star or white dwarf pulls material from a companion star, heating it before it falls in.

The researchers say the discovery could help resolve two long-standing puzzles. Some white dwarf binaries are thought to eventually explode as Type Ia supernovae, which astronomers use to measure the expansion of the universe, but the stars that produce them have never been directly identified beforehand. Co-author Jimmy Irwin of the University of Alabama said spotting such systems before they explode would be valuable. The intense ultraviolet radiation from these sources may also help explain what strips electrons from the gas between stars in some galaxies, a process that influences how quickly new stars form.

Co-author Rosanne Di Stefano of the Center for Astrophysics | Harvard & Smithsonian said the low-energy X-rays are difficult for telescopes to detect, while the ultraviolet radiation is usually absorbed by hydrogen and helium gas between stars, which is why the objects went unnoticed until now.