August 20, 2010
A galactic "super-volcano" in the massive galaxy M87 is erupting and blasting gas outward, as witnessed by NASA's Chandra X-ray Observatory and the National Science Foundation's (NSF) Very Large Array (VLT). The cosmic volcano is being driven by a giant black hole in the galaxy's center and preventing hundreds of millions of new stars from forming.
Astronomers studying this black hole and its effects have been struck by the remarkable similarities between it and a volcano in Iceland that made headlines earlier this year.
At a distance of about 50 million light-years, M87 is relatively close to Earth and lies at the center of the Virgo cluster, which contains thousands of galaxies. M87's location, coupled with long observations over Chandra's lifetime, has made it an excellent subject for investigations of how a massive black hole impacts its environment.
"Our results show in great detail that supermassive black holes have surprisingly good control over the evolution of the galaxies in which they live," said Norbert Werner of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in Palo Alto, California, and the SLAC National Accelerator Laboratory. "And it doesn't stop there. The black hole's reach extends ever farther into the entire cluster, similar to how one small volcano can affect practically an entire hemisphere on Earth."
The cluster surrounding M87 is filled with hot gas glowing in X-ray light, which is detected by Chandra. As this gas cools, it can fall toward the galaxy's center, where it should continue to cool even faster and form new stars.
However, radio observations with the VLT suggest that in M87 jets of energetic particles produced by the black hole interrupt this process. These jets lift up the relatively cool gas near the center of the galaxy and produce shock waves in the galaxy's atmosphere because of their supersonic speed.
The scientists involved in this research have found the interaction of this cosmic "eruption" with the galaxy's environment to be very similar to that of the Eyjafjallajokull volcano, which forced much of Europe to close its airports earlier this year.
With Eyjafjallajokull, pockets of hot gas blasted through the surface of the lava, generating shock waves that can be seen passing through the gray smoke of the volcano. The hot gas then rises up in the atmosphere, dragging the dark ash with it.
In the analogy with Eyjafjallajokull, the energetic particles produced in the vicinity of the black hole rise through the X-ray emitting atmosphere of the cluster, lifting up the coolest gas near the center of M87 in their wake, much like the hot volcanic gases drag up the clouds of dark ash. And just like the volcano here on Earth, shock waves can be seen when the black hole pumps energetic particles into the cluster gas.
"This analogy shows that even though astronomical phenomena can occur in exotic settings and over vast scales, the physics can be very similar to events on Earth," said Aurora Simionescu from the Kavli Institute in Santa Barbara, California.
In M87, the plumes of cooler gas being lifted upward contain as much mass as all of the gas contained within 12,000 light-years of the center of the galaxy cluster. This shows the black hole-powered volcano is efficient at blasting the galaxy free of the gas that would otherwise cool and form stars.
"This gas could have formed hundreds of millions of stars if the black hole had not removed it from the center of the galaxy," said Evan Million from Stanford University. "That seems like a worse disruption than what the airline companies on Earth had to put up with earlier this year.
The eruption in M87 that lifted up the cooler gas must have occurred about 150 million years earlier, but a smaller eruption only about 11 million years earlier produced the shock wave. The Chandra image was based on an observation lasting almost 7 days. X-ray data from ESA's XMM-Newton was also used in this study.