Astrophysicists Detect Extreme Energetic Processes of a Galaxy

A University of Oklahoma team has detected for the first time the most luminous gamma-ray emission from a galaxy. Named ‘Arp 220’, it is the nearest ultra-luminous infrared galaxy to Earth, and it reveals a hidden extreme energetic processes of a galaxy. The first gamma-ray detection of an infrared ultra-luminous galaxy occurs when the most energetic cosmic rays collide with the interstellar medium causing these galaxies to glow, expanding observations to the highest energy ranges.

apr 217

Team leader Xinyu Dai, professor in the Department of Physics and Astronomy at the University of Oklahoma, made the discovery after collecting data using the National Aeronautics and Space Administration’s Fermi Gamma-Ray Space Telescope.

“These galaxies are different because of their immense star formation and extra dust that scatters the light and makes them luminous in the infrared,” said co-author Todd Thompson, professor in the Department of Astronomy and Center for Cosmology and Astro-Particle Physics, Ohio State University.

The team developed a collective methodology used to detect gamma-ray emissions from Arp 220. The massive amount of star formation found in infrared luminous and ultra-luminous galaxies suggest a multitude of stars go supernovae ending in one final immense explosion.

A resulting thunderous outburst accelerates charged particles to relativistic velocity eventuating into cosmic rays, which synthesize to particles and light including gamma-ray emissions. Since cosmic rays are difficult to measure, the larger spectrum of gamma-rays reveal a hidden energy component in galaxies.


Arp 220’s center contains over 200 enormous star clusters. The most massive of these clusters contains enough material to equal 10 million Suns – twice as massive to any comparable star cluster in the Milky Way. The gamma-ray emission is expected to be tractable showing two compact disks in the nucleus of Arp 200, which contains almost all star-formation activities in this galaxy.