Galaxy Sans Dark Matter

ChromaticDragon writes "Astronomers have crunched some numbers on a galaxy to discover that its rotation can be fully explained by the gravity of the observable matter — in effect, this galaxy seems to lack dark matter. This shouldn't come as a total surprise given that one of the stronger observations of Dark Matter was the Bullet Cluster where supposedly a good deal of Dark Matter and good old fashion regular matter had separated."

Comments

Another argument for variability of "constants"

[Ungrounded Lightning]

No (or negligible) dark matter in our galaxy, eh?

When we're looking farther away, we're looking back in time, too. So perhaps the observations could be explained by "constants" of physics (notably the gravitational constant) varying with the age of the universe, rather than by the gravitational pull of some otherwise-unobservable dark matter.

Let's see if "dark matter" is "more dense" the farther away we look... B-)

Re:Fascinating!

[tirerim]

Sure. But most of the galaxies we have observed seem to be made up of a mixture of dark matter and visible matter, given their gravitational characteristics. Finding a galaxy with no matter isn't any sort of physical impossibility, but it's surprising because it's not the norm. If most galaxies contain dark matter, then something unusual must have happened to this one for it not to contain dark matter, and that's interesting; beyond that, the fact that such a thing even could happen may give us insights into the nature of dark matter.

History of Dark Matter

[foxpaws]

I thought I could contribute a bit to the discussion by giving some background on why the theory of dark matter came about.

Vera Rubin's work on galaxy rotation rates is still pretty compelling evidence for dark matter... OR, at least, it shows us that all galaxies do not behave they way we think they should, to be more accurate. People much smarter than my own self have decided that "dark matter" or some sort of mass/force/something that does not emit light or radio waves, etc. (which is why we never noticed it before) must be responsible.

When we look at a solar system like ours, we see that the farther a planet is from the sun, the slower it travels. Not only does it have a much longer way to go, but it doesn't - and according to what we understand, shouldn't - travel as fast.

Vera Rubins decided to check a whole galaxy. What she found did not hold with our understanding. The solar systems, stars and other observable matter near the outside were traveling faster than expected.

Vera Rubin's work, combined with the discovery that the univers appears to be expanding at an accelerating rate, rather than slowing down, kind of kicked off the whole dark matter/dark energy thing.