HD 49798

HD 49798 is binary star in the constellation Puppis about 650 parsecs from Earth. It has an apparent magnitude of 8.3.

HD 49798 was discovered in 1964 to be a rare hydrogen-deficient O class subdwarf. This was identified as a binary star, but the companion could not be detected visually or spectrscopically.

In its vicinity, scientists discovered an X-ray source with the label RX J0648.0-4418. Only the space telescope XMM-Newton was able to identify the radiation causing object. It is a white dwarf with about 1.3 solar masses, in orbit about HD 49798 and rotating once every 13 seconds. This system is considered a likely candidate to explode as a type Ia supernova with a few thousand years.