IRISH ASTRONOMERS have contributed to a major astronomical discovery, the first of its kind to be found. It is a hyperactive “starburst” galaxy where stars explode and others are forming rapidly. Just as importantly, its discovery may help solve the century-old mystery about the source of cosmic rays that reach us from deep space.
The M82 galaxy, also known as the “Cigar Galaxy” was found under the international Veritas (Very Energetic Radiation Imaging Telescope Array System) research collaboration.
This involves 22 institutions around the world including four here – NUI Galway, Cork Institute of Technology, Galway-Mayo Institute of Technology and University College Dublin – said Dr Mark Lang, head of the school of physics at Galway.
“It is an example of Irish scientists taking part in a big international collaboration. We have certainly punched above our weight in this group.”
Veritas uses a telescope with four highly sensitive 12-metre mirrors attached to fast cameras. The telescope scans the sky for the very faint light caused when gamma-ray radiation coming from distant sources strikes the upper atmosphere, Dr Lang said.
It is not visible to the naked eye as the light lasts for no more than one or two billionths of a second, he said. The cameras can capture the image, however, and track back to the gamma-ray source.
It took two years of observations using the Veritas instrument based at the Smithsonian Institution Observatory in Arizona to gather enough information to pinpoint the starburst galaxy M82, lying about 12 million light years away.
This allows astronomers to make inferences about what triggers the release of the gamma rays, which are very high energy cosmic rays.
Cosmic rays strike the Earth all of the time and were detected a century ago, Dr Lang said. Their source was a mystery but the assumption was they came from active galaxies where star formation, supernova star explosions and gamma-ray burst activity was taking place.
The Veritas team publishes their findings this morning in the journal Nature. They have formed a link between the high amount of gamma rays coming from M82 and very active cosmic-ray production within that galaxy.
“This links cosmic-ray acceleration to star formation activity, and suggests that supernovae and massive-star winds are the dominant accelerators [of gamma rays],” the authors write in Nature.
Cosmic rays reach us from all directions but we can’t track to their sources because large magnetic fields make their paths bend, Dr Lang said. Gamma rays only travel in straight lines.
Although very weak, the researchers over two years were able to build up enough data to measure the flux of gamma rays and so infer the flux of cosmic rays needed to produce them.