Just like our own Milky Way Galaxy , the nearest major galaxy M31 has many star systems spewing high energy radiation . High energy X-radiation is visible to certain satellites in Earth orbit such as ROSAT - which took the above picture. The X-ray sources in M31 occur in globular clusters , the spiral arms , and near the galaxy's center. Probably most of these sources are accretion disk binary star systems . M31 has more X-ray sources near its center than our Galaxy, and the reason for this is currently unknown.
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Credit: ROSAT, MPE, NASA