Dark Matter

From Slackerpedia Galactica

Dark Matter is a concern that has negative connotations. For example, "the IAU's demotion of Pluto as a planet is a dark matter indeed."

Must not be confused with gray matter (UK: grey matter). Gray matter is a colloquial term for the cognitive part of the brain, the cerebral cortex. In contrast to dark matter, gray matter is observable, although there is not enough of it in the universe to make one jot of a difference, even if it supposedly more densely packed in the astronomer. Also compare with the term gray area, for example, "the IAU's definition of a planet is a gray area indeed."

It is also the name of Dark Helmet's German mother.

But for astronomy, it is a proposed type of cosmic matter that is unobservable, and does not interact with baryonic matter other than gravitationally. Although it was long considered purely hypothetical, some form of dark matter was a requirement for nearly all modern cosmological models, if they were to match observations. It is also (as far as we know) required to explain the rotation curves of galaxies, where the observed rotation profiles did not match those expected if the only mass in the galaxy was that which was visible in stars or interstellar medium. Other forms of "unseen matter" like MACHOs do not appear to be abundant enough, and alternative cosmologies like modified Newtonian dynamics have not gained much acceptance outside of their original proponents.

Recent observations of the Bullet Cluster of galaxies made with a variety of optical and X-ray telescopes appear to provide the "smoking gun" (cough) for dark matter. The gas profile of the cluster is shaped mainly by hydrodynamic interaction of the baryonic content of the merging subclusters, but the gravitational lensing profile of the cluster appears to be biased towards unseen matter concentrations outside of the gas distribution. The theory is that the baryonic matter of the clusters collided and merged, while the dark matter contents of the two clusters passed straight through the collision.

Also, Futurama's Nibbler excretes it. Useful for powering spaceships, moreso than improbability or wave motion engines.

In the world of observational astronomy dark matter is also known as any unseen object that is tripped over while walking around your telescope.

External Links

Slackerpedia Galactica audio podcast interview w/Dr. Andrey Kravtsov about Dark Matter