Dark Matter Day

Cosmology
History of Science
Nature of Science
STEM
Edward Hessler

Aaarrgghh! Late again. As usual.

In addition to Halloween, October 31 was also International Dark Matter day. I noticed, with some relief that the date was "on or about" but wonder whether November 11 is close to about.

Symmetry magazine provides some pics from the celebration as well as a poster you can download.

Cosmologist Sean Carroll says that the following are the important facts about dark matter: 

It’s dark. Doesn’t interact with electromagnetism, at least not with anywhere near the strength that ordinary charged particles do. 

It’s cold. Individual dark matter particles are moving slowly and have been for a while, otherwise they would have damped perturbations in the early universe. 

There’s a goodly amount of it. About 25% of the energy density of the current universe, compared to only about 5% in the form of ordinary matter. 

It’s stable, or nearly so. The dark matter particle has to be long-lived, or it would have decayed away a long time ago. 

It’s dissipationless, or nearly so. Ordinary matter settles down to make galaxies because it can lose energy through collisions and radiation; dark matter doesn’t seem to do that, giving rise to puffy halos rather than thin galactic discs. 

Here is a short animation on dark matter and the force (Star Wars), with attention to some of their similarities.

For a short primer about dark matter see here.