Connecting dots in the sky


Scientists match up maps of matter and light.


Astrophysicists have found a certain gamma-ray glow in the sky, known as unresolved gamma-ray background (yellow), coincides with cosmic regions that contain a lot of matter (red). 

Daniel Gruen/SLAC/Stanford, Chihway Chang/University of Chicago, Alex Drlica-Wagner/Fermilab

Astrophysicists say they are a step closer to understanding the origin of a faint glow of gamma rays covering the night sky.

They have found that this light is brighter in regions that contain a lot of matter and dimmer where matter is sparser – a correlation that could help them narrow down the properties of exotic astrophysical objects and invisible dark matter.

The international team created the map above by combining a year of data from the Dark Energy Survey (DES), which takes optical images of the sky, with nine years of data from the Fermi Gamma-ray Space Telescope, which observes cosmic gamma rays while it orbits the Earth.

The glow, known as unresolved gamma-ray background, stems from sources that are so faint and far away that researchers can't identify them individually. Yet, the fact that the locations where these gamma rays originate match up with where mass is found in the distant universe could be a key puzzle piece in identifying those sources.

"The background is the sum of a lot of things 'out there' that produce gamma rays,” says Simone Ammazzalorso from the University of Turin, Italy, who co-led the analysis.

“Having been able to measure for the first time its correlation with gravitational lensing – tiny distortions of images of far galaxies produced by the distribution of matter – helps us disentangle them.”

What's really intriguing, adds Daniel Gruen from Stanford University in the US, is that the correlation they measured doesn't completely match their expectations.

"This could mean that we either need to adjust our existing models for objects that emit gamma rays, or it could hint at other sources, such as dark matter."

The study has been accepted for publication in the journal Physical Review Letters.

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  1. https://www.darkenergysurvey.org/
  2. https://fermi.gsfc.nasa.gov/
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