Dance of the galaxies

The Milky Way appears to have been let off in the case of the Large and Small Magellanic Clouds.

The two orbitting dwarf galaxies are presently ensnared in the gravity of the much large Milky Way, but observations show they are linked by a stream of gas and stars. Initial thoughts were this was part of the tearing and chewing process the Milky Way invokes in absorbing the smaller bodies, however, studies of the dynamics of galaxy interactions have shown this is unlikely to have been the case. It is more likely that the two clouds came together before meeting the Milky Way and so became an interacting binary. Then they arrived at our local galaxy and are either in an unusually large orbit or have only just, in galactic lifetime terms, arrived. Full details here.

Meanwhile, researchers at the Argonne National Laboratory have been studying and simulating the collision and merger of galaxy clusters to derive the role, if any, that dark matter plays in the dynamics of the collisions. The particular one being studied is the evolution of the Bullet Cluster. The simulation looks a little like this:

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