NASA's Swift satellite recently detected a rising tide of high-energy X-rays from a source toward the center of our Milky Way galaxy. The outburst, produced by a rare X-ray nova, announced the presence of a previously unknown stellar-mass black hole. /n"Bright X-ray novae are so rare that they're essentially once-a-mission events and this is the first one Swift has seen," said Neil Gehrels, the mission's principal investigator, at NASA's Goddard Space Flight Center in Greenbelt, Md. "This is really something we've been waiting for."/nAn X-ray nova is a short-lived X-ray source that appears suddenly, reaches its emission peak in a few days and then fades out over a period of months. The outburst arises when a torrent of stored gas suddenly rushes toward one of the most compact objects known, either a neutron star or a black hole. /nAn X-ray outburst caught by NASA's Swift on Sept. 16, 2012, resulted from a flood of gas plunging toward a previously unknown black hole. Gas flowing from a sun-like star collects into a disk around the black hole. Normally, this gas would steadily spiral inward. But in this system, named Swift J1745-26, the gas collects for decades before suddenly surging inward. Credit: NASA's Goddard Space Flight Center