It is not unusual in astronomy to detect things and at the moment have absolutely no idea what was detected. For instance, folks who study the highest energy colors of light – gamma rays – have found lots of brief bursts that we now know are related to neutron stars and supernovae. They have also found lots of regularly bright places, like feeding black holes. They’ve even found gamma-ray light coming from star-forming regions. 

What has been a bit frustrating is the faint gamma-ray light that just kind of shines everywhere. Called “empty sky gamma-ray emission”, this is diffuse light that is seen in the otherwise dark areas of the sky. Since the source of the light hasn’t been directly detectable, a team of researchers turned to computer models to see what they could find. 

In a new paper appearing in Nature and led by Matt Roth, researchers describe how a distant background of star-forming galaxies can produce enough gamma rays to explain what is seen while remaining too faint in other wavelengths. This is one of those nice results where everything fits together, nothing new is required, and while we can’t definitively say the paper is right, since we can’t see those galaxies, I’m completely good with this result.

More Information

ANU press release

“The diffuse γ-ray background is dominated by star-forming galaxies,” Matt A. Roth, Mark R. Krumholz, Roland M. Crocker and Silvia Celli, 2021 September 15, Nature