This is the nearest galaxy in which we see evidence of violent activity . The first sign of activity came with the discovery of a small, week radio source in its nucleus. Optical studies showed that a large amount of gas had been ejected above and below the plane of M82 and the velocity of the gas suggested the ejection had started about 1 – 10 million years ago. It has also been found that the radiation from the filaments of ejected gas is strongly polarized. This was first thought to show that the outburst had given rise to optical synchrotron radiation, but more recent work has shown that both the optical continuum and the emission lines are strongly and similarly polarized. As synchrotron radiation cannot generate emission lines, polarized or not, another explanation had to be sought, Evidence of substantial quantities of dust –so much so that the nucleus of M82 can only be penetrated by infra rod wavelengths longer than about 700nm. It is now believed that the dust grains above and below the plane of M82 are aligned by the radiation from the nucleus and that the way in which they .scatter light towards us is responsible for the polarization. As there is no evidence for a bright stellar nucleus, even after the obscuration produced by the dust has been accounted for, it is evident that M82 is not a Seyfert galaxy. There is, however, a very strong infrared source in the nucleus. There are also considerable non-circular motions of the ionized gas throughout the galaxy and it is probable that these motions were also caused by disturbances in the nucleus of M82.

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