January 10, 2012 | 4
AUSTIN, Tex.—One of the great ironies of the universe is that black holes, the ultimate vacuum cleaners, create more of a mess than they clean up. (It is a complaint that many people who finally prevailed on spouses and roommates to clean up after themselves might appreciate.) How is it that, in sucking up surrounding material, they squirt much of it right back out? A team of astronomers has now caught a black hole in the act.
The hole in question, a modest-size one located near the center of our galaxy known as H1743-322, had been known to flare up in x-rays every eight months or so, presumably as it periodically munched on a nearby star. Gregory Sivakoff of the University of Alberta and his colleagues kept watch on the black hole in mid-2009 using the Very Long Baseline Array (a worldwide array of radio telescopes) and the Rossi X-ray Timing Observatory (a satellite that NASA shut down last week after 16 years in operation). On May 28 and 30 and June 2, all seemed normal. But on June 5, the radio telescopes spotted bright knots of material flying away in opposite directions. By June 6, the knots had moved a substantial distance, implying a velocity of a quarter of the speed of light. Working backward, the team deduced the material had been shot out on June 2, 2009, at about 10:00 P.M. Universal Time, give or take half a day. The researchers announced their finding today during a meeting of the American Astronomical Society being held here.
The x-ray images, meanwhile, showed some unusual goings-on in the disk of material swirling around the black hole. On May 28 and 30, there was a spot in the disk revolving once per second. On June 2, the spot sped up threefold—and after the ejection, there was no spot at all. Sivakoff said it was a chunk of orbiting material that death-spiraled into the hole.
The researchers still need to sort out exactly how the infalling spot turned to outflying knots. One idea, Sivakoff said, is that material dragged along magnetic field lines on its way in. At some point, the field lines snapped like rubber bands; north- and south-oriented lines reconnected, unleashing energy that flung particles outward. Another idea is that the plummeting material created a shock wave that energized outgoing stuff.
Through such processes, black holes are the most powerful engines in the universe, converting gravitational energy to heat, light and kinetic energy of particles. In return for untidiness, they keep the universe a vibrant place.