Swift Catches X-ray Activity at the Galaxy's Center

The innermost region of our galaxy lies 26,000 light-years away in the direction of the constellation Sagittarius. At the center of it all lurks Sgr A* (pronounced "saj a-star"), a behemoth black hole containing 4 million times the sun's mass.

Sgr A* regularly produces bright X-ray flares today, but astronomers know it was much more active in the past.

To better understand its long-term behavior, the Swift team began regular observations of the galactic center in February 2006. Every few days, the spacecraft turns toward the inmost galaxy and takes a 17-minute-long "snapshot" with its X-Ray Telescope (XRT).

Swift's XRT has now detected six bright flares, during which the black hole's X-ray emission brightened by up to 150 times for a couple of hours. These new detections, in addition to four found by other spacecraft, enabled astronomers to estimate that similar flares occur every five to 10 days.

The Swift XRT team is on the lookout for the first sign that a small cold gas cloud named G2, which is swinging near Sgr A*, has begun emitting X-rays. This is expected to start sometime in spring 2014. The event will unfold for years and may fuel strong activity from the monster black hole.

The monitoring campaign has already yielded one important discovery: SGR J1745-29, an object called a magnetar. This subclass of neutron star has a magnetic field thousands of times stronger than normal; so far, only 26 magnetars are known. A magnetar orbiting Sgr A* may allow scientists to explore important properties of the black hole and test predictions of Einstein’s theory of general relativity.