NASA | X-ray Nova Reveals a New Black Hole in Our Galaxy

On Sept. 16, NASA's Swift satellite 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.
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 torent of stored gas suddenly
rushes toward one of the most compact objects
known, either a neutron star or a black hole.
Named Swift J1 745-26 after the coordinates of its sky
position, the nova is located a few degrees from the
center of our galaxy toward the constellation
Sagittarius. While astrononmers do not know its
precise distance, they think the object resides about
20,000 to 30,000 light-years away in the galaxy's inner
region. The pattern of X-rays from the nova signals
that the central object is a black hole.
Ground-based observatories detected infrared and
radio emissions, but thick clouds of obscuring dust
have prevented astronomers from catching Swift
J1745-26 in visible light.
The black hole must be a member of a low-mass
X-ray binary (LMXB) system, which includes a normal,
sun-like star. A stream of gas flows from the normal
star and enters into a storage disk around the black
hole. In most LMXBs, the gas in the disk spirals
inward, heats up as it heads toward the black hole,
and produces a steady stream of X-rays.