Coloured X-ray image of the spiral galaxy M81 (NGC 3031). Several X-ray sources are seen here as bright spots; the brightest spot at centre coincides with the compact nucleus of the galaxy. The other sources seen in this image are likely to be binary star systems in which a neutron star or a black hole accretes matter from its companion star. The large distance of M81 from the Earth (10.5 million light years) has prevented the unambiguous identification of these sources. M81 belongs to the M81/M82 cluster of galaxies that contains about 30 members. The image was taken with the ROSAT astronomical satellite.
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