A new stellar-mass black hole has been discovered in our Milky Way galaxy by Swift satellite, U. S. space agency NASA announced Friday.

High-energy X-rays emanating from a source towards the center of our galaxy were observed, indicating the presence of a previously unknown black hole.

"Bright X-ray novae are so rare that they're essentially once-a- mission events and this is the first one Swift has seen," according to Neil Gehrels, the mission's principal investigator at NASA's Goddard Space Flight Center. "This is really something we' ve been waiting for."

An 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.

The source triggered Swift's Burst Alert Telescope twice on September 16, and once again on the next day. The nova, or Swift J1745-26, is located a few degrees from the center of our galaxy toward the constellation Sagittarius. Astronomers believe the object resides about 20,000 to 30,000 light-years away in the galaxy's inner region.

The nova peaked in X-rays -- energies above 10,000 electron volts, or several thousand times that of visible light -- on September 18, when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant that serves as a calibration target for high-energy observatories and is considered one of the brightest sources beyond the solar system at these energies. As it dimmed at higher energies, the nova brightened in the lower-energy emissions detected by Swift's X-ray Telescope.

"The pattern we're seeing is observed in X-ray novae where the central object is a black hole," said Boris Sbarufatti, an astrophysicist at Brera Observatory in Milan, who currently is working with other Swift team members at Pennsylvania State University. "Once the X-rays fade away, we hope to measure its mass and confirm its black hole status."