April 25, 2008
Secrets of Supermassive Black Holes Revealed
A team of international astronomers announced this week they had obtained images of a supermassive black hole just as it was ejecting an enormous jet of supercharged particles traveling at the speed of light.
The images, obtained by powerful telescopes, confirmed what many scientists had believed about how these jets are formed, the astronomers said.
A black hole is a concentration of mass so dense that little can escape its gravitational pull. Supermassive black holes form the core of many galaxies.
The international team, led by Alan Marscher of Boston University, used the National Radio Astronomy Observatory's Very Long Baseline Array -- a system of 10 radio telescopes "“ and aimed it towards the galaxy BL Lacertae, where a supermassive black hole known as a blazar had been suspected of spewing out a pair of forceful streams of plasma some 950 million light years from Earth.
A light year is the distance light travels in a year, or about 6 trillion miles.
Observing an outburst from late 2005 to 2006, the team obtained close-up views and captured images of bursts of photons oriented precisely as astronomers had predicted using theories about twisted magnetic fields of black holes.
"We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated," Marscher told Reuters.
"It helps us understand how these objects are able to accelerate particles up to the near velocity of light," said University of Michigan astronomy professor Hugh Aller, who worked on the project with Marscher, in a telephone interview with Reuters.
Aller explained that while some objects fall into the black hole, others get shot out at very high velocities. The trick is capturing enough data at the proper time in order to better understand this phenomenon, he said, comparing the acceleration process to the output of a jet engine.
"We never know when these objects will go off. It depends on when the object falls into it," he said.
"We think it is focused by a nozzle of sorts and it comes out at us."
The researchers reported their findings in the April 24 issue of Nature.
Image Caption: Artist's conception of region near supermassive black hole where twisted magnetic fields propel and shape jet of particles (Credit: Marscher et al., Wolfgang Steffen, Cosmovision, NRAO/AUI/NSF).
On the Net:
Watch Video of Black-Hole-Powered Jet (Credit: Cosmovision, Wolfgang Steffen) . Download: NTSC Format (90MB) | PAL Format (90MB)