January 8, 2013
Massive Belch From Neighboring Galaxy Catches Astronomers By Surprise
April Flowers for redOrbit.com - Your Universe Online
A team of scientists conducting a long-term study of molecules in galaxies gained a tantalizing look at what is likely a powerful belch by a gorging black hole at the center of a changing galaxy.
"The discovery was entirely serendipitous. Our observations were spread over a few years, and when we looked at them, we found that one galaxy had changed over that time from being placid and quiescent, to undergoing a hugely energetic outburst at the end," said Robert Minchin, of Arecibo Observatory in Puerto Rico.
The research team was using the William E. Gordon 305-meter Telescope at Arecibo when they observed NGC 660, a spiral galaxy 44 million light-years away in the constellation Pisces, experiencing a massive outburst ten times brighter than the largest supernova.
Once they had identified the outburst, the team continued to observe NGC 660 and sought to determine the cause using an international network of telescopes to make a detailed image of the galaxy.
"High-resolution imaging is the key to understanding what's going on," said Emmanuel Momjian, of the National Radio Astronomy Observatory (NRAO). "We needed to know if the outburst came from a supernova in this galaxy or from the galaxy's core. We could only do that by harnessing the high-resolution imaging power we get by joining widely-separated radio telescopes together."
The telescope network, called the High Sensitivity Array (HSA) is composed of the National Science Foundation's Very Long Baseline Array (VLBA). The VLBA is a continent wide system of ten radio telescopes ranging from Hawaii to the Virgin Islands; the Arecibo Telescope; the NSF's 100-meter Green Bank Telescope in West Virginia; and the 100-meter Effelsberg Radio Telescope of the Max Planck Institute for Radio Astronomy in Germany.
"By adding the large collecting area of the three big dishes to the VLBA, we got the images much more quickly. What we did with the HSA in less than half a day would have taken nearly nine days with the VLBA alone," Momjian said.
The team did not expect the complexity of the resulting images. They expected to see either the ring of an expanding supernova or a jet of superfast material from the galaxy's core. What they saw, instead, were five sites of bright radio emission. One site was at the galaxy's center, with two on either side.
"The most likely explanation is that there are jets coming from the core, but they are precessing, or wobbling, and the hot spots we see are where the jets slammed into material near the galaxy's nucleus," said Chris Salter, of Arecibo Observatory. "To confirm this, we will continue to observe the galaxy with the HSA over the next few years," he added.
If the team's jet hypothesis is correct, the outburst was caused by material pulled into the supermassive black hole at the center of the galaxy. Such material would form a rapidly spinning disk around the black hole. This disk would eventually be pulled into the black hole, generating jets of particles blasting outward at nearly the speed of light.
In a similar situation, astronomers are watching a gas cloud in our own Milky Way galaxy, expecting it to fall into the central black hole in the middle of this year.
The results of this study were reported at the recent American Astronomical Society meeting in California.