November 21, 2013
Milky Way’s Black Hole Shows Off It’s Jet Of High-Energy Particles
Brett Smith for redOrbit.com - Your Universe Online
Many supermassive black holes emit a jet of high-energy particles as a byproduct of engulfing large quantities of mass and energy, and NASA researchers have just discovered that the supermassive black hole at the center of the Milky Way is no different.
Using observations from NASA's Chandra X-ray Observatory and the National Science Foundation's Very Large Array (VLA) radio telescope, a team of Chinese and American astrophysicists have found strong evidence that the Milky Way’s Sagittarius A* (Sgr A*) black hole is sending out a relatively faint stream of high-energy particles, according to a report in The Astrophysical Journal.
Astrophysicists have said that the jets are created when some material falling toward a black hole is redirected outward.
"For decades astronomers have looked for a jet associated with the Milky Way's black hole. Our new observations make the strongest case yet for such a jet," said study author Zhiyuan Li of Nanjing University in China.
Particle jets can be produced by both young stars and massive black holes. These streams play major roles in sending energy away from the gravitational pull of the central object and controlling the rate of new star formation on a galactic scale.
"We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole's spin axis," said study author Mark Morris, an astronomer at UCLA. “This gives us important clues about the growth history of the black hole.”
The study team found that the spin axis of Sgr A* is parallel to the rotation axis of the Milky Way, an indication that gas and dust have traveled slowly into Sgr A* over the past 10 billion years. If the Milky Way had recently collided with large galaxies and their central black holes had merged with Sgr A*, the particle jet could be pointing in any direction.
The researchers said the particle jet seems to be hitting gas near Sgr A*, producing X-rays that were picked up by Chandra and radio emissions detected by the VLA. They also noted that the energy signature in X-rays of Sgr A* bears a resemblance to jets coming from supermassive black holes in other galaxies.
NASA scientists said it’s not surprising the jet appears frail as Sgr A* is presently believed to be consuming very little material. Unlike other black holes, Sgr A* is not producing a jet in the opposite direction, possibly because gas or dust is making observations from Earth difficult or simply due to a lack of material.
While the region around Sgr A* has been quiet recently, a previous study based on Chandra data showed that it was at least a million times brighter just a few hundred years ago.
"We know this giant black hole has been much more active at consuming material in the past," said study author Frederick K. Baganoff, a physicist at MIT. “When it stirs again, the jet may brighten dramatically.”