Research Highlight

Gamma-ray nursery in Milky Way

doi:10.1038/nindia.2012.45 Published online 29 March 2012

Researchers have shed new light on how ultrahigh-energy cosmic rays (UHECRs) spawn high-energy gamma rays at the centre of the Milky Way galaxy. The study uses mathematical calculations to explain the processes that generate energetic gamma rays at the heart of the Milky Way, around 26,000 light years away from Earth.

Most sources of UHECRs, such as supernova remnants, are located near the centre of the Milky Way. These rays — streams of high-energy protons — hurtle through space and react with matter such as the heavy-atom nuclei and hydrogen atoms floating between stars. These interactions create energetic gamma rays.

To find where and how UHECRs produce and aid the generation of energetic gamma rays inside the Milky Way, the researchers calculated the flux of peta-electronvolt (PeV) gamma rays emanating from UHECRs sources such as supernova remnants. For this, they chose cosmic ray sources near the galactic centre. They found that these gamma rays are produced in interactions between galactic hydrogen nucleons and the iron nuclei and protons found in cosmic rays.

Some UHECRs may be trapped in magnetic fields at the galactic centre, thus forming galactocentric secondary gamma rays.

"After observing point sources of PeV gamma rays in our galaxy, it may be possible that our galaxy also contains sources that produce cosmic rays with exa-electronvolt energies," says lead researcher Nayantara Gupta from the Astronomy and Astrophysics Group of Raman Research Institute, Bangalore, India.


  1. Gupta, N. et al. PeV gamma rays from interactions of ultra high energy cosmic rays in the Milky Way. Astropart. Phys. 35, 503-507 (2012)