posted                      

quote:

---

Originally posted by Balaam Xumucane:
dork matter.

---

posted                      

quote:

---

given that we haven't yet determined just how much regular matter there is even in our own neighborhood

---

Compared to the mass of stars, finding ANY planets or asteroids is insignificant comparatively. In these locales, Jupiter is not even 0.1% of the mass of Sol itself!

A single galaxy has hundreds of millions -- or even billions -- of stars in it. Compared to that, who the hell cares if they miss a couple dozen or hundreds of stars? A single galactic cluster has several dozen galaxies in it, ranging in size from the dwarves that have only a few dozen thousand stars in them, to the truly massive ones that have billions.

Face it -- on the scale of the universe, individual stars are totally and completely insignificant. Take a look at this enlightening Map of the Universe within 14 billion light-years and try zooming in to see how close you need to get before you can see anything recognizable.

The simple fact is, that scientists can fairly accurately measure mass without needing to find every single star ahead of time. They can observe how other bodies are pulled by yet-unseen objects. They can measure the apparent brightness of Cepheid variables, which have a very specific and well-known period-to-luminosity relationship, letting astronomers determine pretty accurate distances to other galaxies. They can measure the Doppler shifts of emission lines from distant galaxies to actually determine their rotational speeds, and therefore also their collective mass.

If you know anything about astronomy in the large-scale universe at all, G2K, you'd know that it's impossible to explain the rotation of spiral galaxies like the Milky Way without dark matter. Without dark matter, a spiral galaxy could not maintain its uniform shape over time, because the stars would all have differing orbital velocities -- and stars orbiting further out from the galactic core would orbit at a much slower speed. (This is exactly why Mercury whips around the sun in less than two months, while it takes Pluto 250+ years to make a single orbit -- the same effect should be seen in the Milky Way, which would rip the spirals apart within a few million years.) For a spiral galaxy to maintain its shape, all of the stars in its spiral arms must have about the same orbital velocity. And that requires the presence of a large, previously-undetected mass that is concentrated around the edge (and beyond the edge) of the visible galaxy to affect the velocities of all those stars.

If you want more, I'd recommend looking at an astronomy textbook. I took an astronomy class last spring at the University of Delaware (taught by a professor who participated in the 2MASS survey, one of the most famous and productive civilian astronomy projects in the past decade). The textbook came with the CD for all of its material in it -- I'd be happy to send you a copy of the HTML file for the chapter on dark matter. Maybe after reading that, you can know what you're talking about.

Dark matter is not just some bizarre theory made up for the amusement of astronomers, so they can giggle at everyone who tries to report on their studies. It's a bizarre theory that tries to explain bizarre happenings in the universe. (I'd be willing to bet that a lot of scientists considered Einstein's theories as very bizarre before THEY were proven...)

Oh, and that "ring" of matter you alluded to was actually the Sagittarius Dwarf Galaxy, not one of the Magellanic Clouds...

--------------------
“Those people who think they know everything are a great annoyance to those of us who do.” — Isaac Asimov
Star Trek Minutiae | Memory Alpha