Starburst Galaxies (3)

The cause of the M82 starburst is almost certainly the interactions of M82 with other galaxies in the M81 group. In particular, the present starburst is thought to have resulted from a tidal interaction of M82 with the M81 galaxy. The neutral hydrogen bridge between the two galaxies that we saw in the radio-frequency image is also the result of that encounter.

The tidal episode with M81 presumably channeled large clouds of hydrogen gas to the center of M82 by a mechanism only partially understood (see the adjacent animation for one possible mechanism), and the increased density triggered the starburst. One piece of supporting evidence for this picture is that the spiral M81 is a significant X-ray source. The X-rays coming from M81 could be explained by a central black hole accreting a solar mass of matter every 10,000 to 100,000 years. We may hypothesize that the collision triggered the starburst in M82 by channeling gas to its center and also diverted an increased flow of gas to a massive black hole in the center of M81. The accretion of that gas onto the black hole then produces the X-rays that are observed coming from M81.