Spotting dark matter by the way it moves

If I seem a little obsessed with dark matter at the moment, it's only because there is so much interesting stuff going on right now. But I can give it up any time—really! As I reported last month, there has been a lot of excitement among astrophysicists and cosmologists because there seems to be more gamma rays than expected coming from various places, including near the center of the Milky Way and other galaxies. Unfortunately, as I also reported, it seems very difficult to absolutely rule out other possible sources for these extra gamma rays. In particular, there is the problem of unresolved sources. These could be gas clouds or other emitters that we simply haven't spotted in other observations.

The obvious solution is to simply keep looking, using other telescopes that look at the sky at other parts of the electromagnetic spectrum to rule out each and every possible source. Some new research tells us how the gamma ray signal may hold much of the evidence already, however. We just need to look closely.

Watching matter move

The idea comes down to how matter moves. The fact that dark matter doesn't really do anything but suck, gravitationally speaking, means that it doesn't really follow the cool kids around, either. When ordinary matter gets close to another bit of ordinary matter, it says hello. It does the equivalent of standing in the middle of the supermarket aisle having a long conversation about the health and happiness of both parties' electrons. Along with gravity, this meeting doesn't just cause matter to clump together, it also causes it to move together. So in our spiral galaxy, it isn't just the stars that rotate around a common center of mass. All the ordinary matter rotates around that common center of mass, too.

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