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Swift discovers new black hole in Milky Way

Paul Sutherland, Feature writer
Oct 7, 2012, 7:00 UTC

Sen—A powerful X-ray observatory operated by NASA has discovered a new black hole that would otherwise have gone unnoticed in our Milky Way galaxy.

The high-energy outburst, produced by a rare X-ray nova, was observed by the Swift telescope and was caused by a rush of gas into the cosmic plughole.

Swift, which has been observing violent events in the Universe since its launch in November, 2004, is mainly kept busy observing so-called Gamma Ray Bursts (GRBs) billions of light-years away.

The joint UK, US and Italian Swift satellite was designed to observe such high energy explosions which occur nearly once a day at random locations across the sky. They are thought to be produced by the birth of black holes or the death of stars.

The surprise X-ray nova, detected towards the centre of our home galaxy, is a much rarer event and its discovery has excited the mission team. It is not to be confused with the far greater Supermassive Black Hole that lies at the heart of our galaxy.

Neil Gehrels, Principal Investigator for the mission, from NASA's Goddard Space Flight Center in Greenbelt, Maryland, said: "Bright X-ray novae are so rare that they're essentially once-a-mission events and this is the first one Swift has seen. This is really something we've been waiting for."

Swift's Burst Alert Telescope was triggered twice on the morning of September 16, and once again the next day by the X-ray nova. It has been named Swift J1745-26 after the coordinates of its position in the sky in the constellation of Sagittarius.

It is thought to lie about 20,000 to 30,000 light-years away in the inner part of the galaxy. Telescopes on the ground detected infrared and radio emissions from the event but it was hidden from optical view by thick clouds of obscuring dust.

The nova reached its bright X-ray peak on September 18 when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant in Taurus that lies within our own galaxy.

NASA video about the black hole discovery

Astrophysicist Boris Sbarufatti, of Brera Observatory in Milan, Italy, commented: "The pattern we're seeing is observed in X-ray novae where the central object is a black hole. Once the X-rays fade away, we hope to measure its mass and confirm its black hole status."

An international team has to stay alert for the random alerts from Swift when it discovers an explosion somewhere in the Universe. One of them is Dr Phil Evans, of the University of Leicester, who gets messages sent day and night direct to his mobile phone.

He told Sen: "Even if it is the middle of the night, I have to scurry straight to my computer and sit there shivering, along with others in our international team, as limited amounts of data are sent to tell us the nature of the burst, where it is, how bright and whether it is fading."

NASA launched a new X-ray space telescope called NuSTAR in June.