Dark, Miniature Galaxies

chill writes "CNN is reporting that "Scientists have discovered evidence that hordes of dark, miniature galaxies surround ordinary galaxies, lending credence to the theory that the universe is comprised mostly of cold, dark matter." The study was partly funded by NASA and the U.S. DOE."

More and more...

[Chasing Amy]

It's looking more and more like the perennial complaints by cosmologists and other physicists and astronomers that there's too much mass in the universe for it all to be accounted by visible galaxies, is holding true.

Yes, the mass of certain neutrinos and other "nearly-massless" particles does figure in, just like we've been theorizing and hearing for a long time. However, we are continually finding more and more of this evidence that there are other sources of mass in dark matter.

It'll be interesting to see the theories on what these "dark matter galaxies" are. Is it some form of dark baryonic matter? Or something else? Quite exotic, either way...

Re:More and more...

[Anonymous Coward]

These satellite galaxies can only help explain the orbital behavior of galactic clusters. To explain the rotation *within* a galaxy, you need more mass *inside* the galaxy.

So it's just not a matter of finding more mass, the mass needs to be located where it is missing.

Dark Matter Overview

[rlotun]

For those of you, like me, who have only a cursory knowledge of Dark Matter check this overview of Dark Matter [ucla.edu]

Re:Dark Matter Overview

[Radical Rad]

Does anyone know why we haven't been able to detect these directly? Why are they dark, are they enshrouded in dust? This story fits with other info I've read recently such as some gamma ray bursts being detected close by and clouds of hydrogen 'raining down' onto the galactic center from outside the plane of the galaxy. But what do they think is the reason for their invisibility? If it is due to dust then wouldn't our view of most of the sky be diminished?

Re:Color distortion?

[mmarlett]

Okkaaay ... No one said anything about the life-sustaing capacities of dark matter, so I'm not sure what to tell you on that one. Scientist learn about what is in stars / planets by breaking apart the light that comes from / is reflected off of them. It's called spectroscopy, and you can learn about the basics of it here [fsnet.co.uk]. But the long and the short of it is that what they are talking about is most certainly "scientifically" proven. It's all pretty simple once you do your homework. Visit a local telescope: even the most low-rent ones have a prism, a light bulb a few filters to show you how to split light to figure out its spectra. It's a fundamental of astronomy that astronomers tend to gloss over because lay people just get glassy eyed if they try to explain it every time.

Re:Color distortion?

[texchanchan]

You can build your own spectroscope and see the spectral lines in sunlight with:
- Piece of diffraction grating, the non-aluminized, see-through kind
- Box that toothpaste came in
- Tape and office supplies

Cut a round 1-cm hole in one end of the long, squarish box. Tape the diffraction grating over it.

Cut a narrow slit, with an X-Acto or similar knife, in the other end.

Now go look at something that lights up by heating gas. This would be either the sun or a fluorescent light, or a mercury-vapor light, etc. Look through the end with the diffraction grating. Compare the sun with a fluorescent--That's one of the ways they can tell what's in a star without going there.

Here's how to build a bigger one [nso.edu] with some links, but the toothpaste box one, you can carry around and impress your friends. (One way or the other.) Link from that page about a spectroscope made from an old CD [colostate.edu].

The galaxy is on Orion's belt?

[lilo]

Okay, maybe not quite that miniature. :)

Cold, Dark matter here on earth!

[Muad'Dave]

So that's what my wife is made of! I have to keep the furnace on 'broil' in the winter, and I've seen her step into the shade of a palm tree in the Caribbean and start shivering. Who should I send a skin sample to?

Details?

[Gaijinator]

The CNN is shy on details, so anyone who is more well-versed in dark matter is welcome to correct my terrible errors that I'm sure to make. I won't note the parts I may be wrong in, though, since I could be wrong in nearly all of them.

Now, gravitation (esp. gravitational lensing) is the only way to detect dark matter. The article shows that the gravitational lens is a "bright" galaxy. So how did they determine that these dark midget galaxies exist? They don't radiate light to be bent by the lens, and unless I'm terribly mistaken, the little circles around the larger one in the image [cnn.net] are in fact the same object, but distorted by the gravitational field of the central galaxy.

As for the second reason dark matter is supposed to exist (that the universe just isn't heavy enough): can't the stars/galaxies/clusters simply be more dense with ordinary matter than we thought? (This would require that the matter be colder than we thought in space, so that the total radiation corresponds with the experimental values).

In conclusion, for those who know about dark matter: why does it have to exist?