Compact sources as the origin of the soft γ-ray emission of the Milky Way

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Abstract
The Milky Way is known to be an abundant source of γ-ray photons1, now determined to be mainly diffuse in nature and resulting from interstellar processes2. In the soft γ-ray domain, point sources are expected to dominate, but the lack of sensitive high-resolution observations did not allow for a clear estimate of the contribution from such sources3,4. Even the best imaging experiment5 revealed only a few point sources, accounting for about 50% of the total Galactic flux6. Theoretical studies were unable to explain the remaining intense diffuse emission7,8. Investigating the origin of the soft γ-rays is therefore necessary to determine the dominant particle acceleration processes and to gain insights into the physical and chemical equilibrium of the interstellar medium7. Here we report observations in the soft γ-ray domain that reveal numerous compact sources. We show that these sources account for the entirety of the Milky Way's emission in soft γ-rays, leaving at most a minor role for diffuse processes.