SMITHSONIAN INSTITUTION / SCIENCE PHOTO LIBRARY SMITHSONIAN INSTITUTION / SCIENCE PHOTO LIBRARY
X-ray image showing sources of x-ray emission in the central region of the Andromeda Galaxy (M31). Located at a distance of 2.2 million light years, M31 is the closest major galaxy to our own Milky Way. It is a spiral galaxy like the Milky Way & the dominant member of our Local Group of galaxies. The x-ray sources in this picture are mostly binary star systems consisting of a neutron star with an old red giant companion; their x-ray emission varies considerably. The image was recorded by the High Resolution Imager (HRI) x-ray telescope on the Einstein Observatory satellite.
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