BLACK HOLE
ATLANTA - The dramatic tantrum last fall from an often-overlooked star has betrayed the existence of the nearest black hole yet discovered in the Milky Way -- one that should be put in a class all its own, a team of astronomers announced Friday.
The black hole, which is associated with a visible star called V 4641, is being called a micro-quasar because it exhibited for a few days in September the brilliant behavior associated with quasars. It sent out tremendous bursts of X-ray radiation and shot out jets of plasma at some 90 percent the speed of light, said Robert Hjellming, of the National Radio Astronomy Observatory.
Hjellming and colleagues from the Massachusetts Institute of Technology made the announcement here at the meeting of the American Astronomical Society.
Quasars are thought to be black holes billions of times more massive than the sun that lie at the heart of active galactic nuclei. They are extremely energetic X-ray emitters that shoot out tremendous fountains of plasma at velocities approaching the speed of light. These jets stretch for thousands of light-years, puzzling astrophysicists who must struggle to answer how black holes provide the oomph and direction for such powerful columns. (A light-year is 5.88 trillion miles.)
Although V 4641 is billions of times smaller than any quasar -- weighing somewhere between three and 10 solar masses -- astronomers who were looking at the object recognized the behavior. Only three other black holes have earned the micro-quasar distinction, but this is the closest one ever seen. It lies just 1,600 light-years from Earth on the way to the center of the Milky Way in the direction of the constellation Sagittarius.
The object drew tremendous attention from astronomers last September after it erupted in a giant X-ray burst, dimmed, and then fired to life again the following day. (Click here to read space.com's coverage of the burst.)
Within several hours of its initial detection, X-ray-observing satellites and radio telescopes around the world were targeting the object. Most were just in time to catch a few hiccups of activity and watch as the emissions faded out of sight.
Using the Very Large Array, a collection of 27 radio antennas in the New Mexico desert, Hjellming obtained a set of radio images that revealed the objects near-light-speed jets. (To read more about that discovery and what it tells physicists about black holes, see space.com's October 25 article.)
Now, Hjellming has released a set of images that show just how fast the objects jets faded.
http://www.space.com/scienceastronomy/astronomy/v4641_microquasar_000114.html