The scientists were conducting a long-term study of molecules in galaxies when one of the galaxies showed a startling change. "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.
The scientists were using the National Science Foundation's (NSF) 305-meter William E. GordonTelescope at Arecibo for their study when they discovered the outburst in NGC 660, a spiral galaxy 44 million light-years distant in the constellation Pisces. The outburst was ten times brighter than the largest supernova, or exploding star. They reported their findings at the American Astronomical Society's meeting in Long Beach, California.
After detecting the outburst, the team continued to observe NGC 660 with the Arecibo Telescope, and also sought to determine the cause of the outburst 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 astronomers used a network called the High Sensitivity Array (HSA), composed of the NSF'sVery Long Baseline Array (VLBA), 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.