A connection between star formation activity and cosmic rays in the starburst galaxy M82 (original) (raw)

Although Galactic cosmic rays (protons and nuclei) are widely believed to be dominantly accelerated by the winds and supernovae of massive stars, definitive evidence of this origin remains elusive nearly a century after their discovery [1]. The active regions of starburst galaxies have exceptionally high rates of star formation, and their large size, more than 50 times the diameter of similar Galactic regions, uniquely enables reliable calorimetric measurements of their potentially high cosmic-ray density [2]. The cosmic rays produced in the formation, life, and death of their massive stars are expected to eventually produce diffuse gamma-ray emission via their interactions with interstellar gas and radiation. M 82, the prototype small starburst galaxy, is predicted to be the brightest starburst galaxy in gamma rays [3, 4]. Here we report the detection of >700 GeV gamma rays from M 82. From these data we determine a cosmic-ray density of 250 eV cm -3 in the starburst core of M 82, or about 500 times the average Galactic density. This result strongly supports that cosmic-ray acceleration is tied to star formation activity, and that supernovae and massivestar winds are the dominant accelerators. M 82 is a bright galaxy located approximately 12 million light years from Earth, in the direction of the Ursa Major constellation [5]. For hundreds of millions of years, M 82 has been gravitationally interacting with nearby galaxies, including the larger spiral galaxy M 81 [6]. Over time, interactions with these neighbours have deformed M 82, creating an active starburst region in its centre with a diameter of ~1000 light years [7].

Sign up for access to the world's latest research.

checkGet notified about relevant papers

checkSave papers to use in your research

checkJoin the discussion with peers

checkTrack your impact