X-Ray Nova Reveals A Black Hole Surprise
October 5, 2012

New Black Hole Discovered In Milky Way

[ Watch the Video: X-ray Nova Reveals a New Black Hole in Our Galaxy ]

Lee Rannals for redOrbit.com - Your Universe Online

A new stellar-mass black hole has been discovered in our galaxy by NASA's Swift satellite.

High-energy X-rays emanating from a source towards the center of our Milky Way 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. "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 on September 18, when it reached an intensity equivalent to that of the famous Crab Nebula.

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. "Once the X-rays fade away, we hope to measure its mass and confirm its black hole status."

The black hole appears to be a member of a low-mass X-ray binary (LMXB) system, which includes a normal, sun-like star. In most of these systems, the gas in the disk spirals inward, heats up as it heads toward the black hole and produces a streaky stream of X-rays.

However, under certain conditions, stable flow within the disk depends on the rate of matter flowing into it from the companion star.

At certain rates, the disk fails to maintain a steady internal flow and instead flips between two dramatically different conditions.

"Each outburst clears out the inner disk, and with little or no matter falling toward the black hole, the system ceases to be a bright source of X-rays," John Cannizzo, a Goddard astrophysicist, said in the release. "Decades later, after enough gas has accumulated in the outer disk, it switches again to its hot state and sends a deluge of gas toward the black hole, resulting in a new X-ray outburst."