Astronomers have uncovered that a well-known X-ray binary, whose exact nature has been a mystery to scientists until now, is actually a hidden ultraluminous X-ray source. The study is published in Nature Astronomy. Astronomers have uncovered that a well-known X-ray binary, whose exact nature has been a mystery to scientists until now, is actually a hidden ultraluminous X-ray source. The study is published in Nature Astronomy. Astronomy Phys.org – latest science and technology news stories