Astronomers have found that a diffuse X-ray glow in our galaxy is not generated by hot gas but rather it's radiating from old stars that have yet to be counted. There could be roughly a billion stars we didn't know about in the Milky Way, they said Wednesday. The discovery, if confirmed, "would have a profound impact on our understanding of the history of our galaxy, from star-formation and supernova rates to stellar evolution," according to a statement released by NASA.