Dark Matter

The New York Times had a science story Milky Way and Neighbor Seen to Merge . It seems a dwarf galaxy is in the process of merging with our galaxy.

But the story contained something that interested me more - indirect evidence of dark matter. Quoting

.... another group of researchers said they had an explanation for a mysterious warp in the disk of the Milky Way that has baffled scientists for decades.

Leo Blitz, professor of astronomy at the University of California, and his colleagues Evan Levine and Carl Heiles charted the warp and found evidence that it is a ripple or vibration set up by two small galaxies that circle the Milky Way. These satellite galaxies, called the Magellanic Clouds, cause vibrations at certain frequencies as they pass though the edges of the Milky Way, the researchers said.

It was previously believed, Dr. Blitz said, that the Magellanic Clouds, with their combined mass being only 2 percent that of the Milky Way, were too small to influence their neighboring galaxy. However, he said, when the Milky Way's dark matter is taken into account, the motion of the small galaxies can create a wake that influences the larger one. ...According to a computer model created with Martin Weinberg, an astronomy theorist at the University of Massachusetts, Amherst, dark matter spreading from the Milky Way disk with the gas layer can enhance the gravitational influence of the Magellanic Clouds as they pass through it.