Space.com (December 21, 2009)
"When the very first stars lit up, they may have been fueled by the dark matter that has long eluded scientists.
"These 'dark stars,' first born nearly 13 billion years ago, might still exist today. Although they would not shed any visible light, astronomers might detect these invisible giants — some 400 to 200,000 times wider than our sun and 500 to 1,000 times more massive — because they should spew gamma rays, neutrinos and antimatter and be linked with clouds of cold, molecular hydrogen gas that normally would not harbor such energetic particles.
"If scientists find these stars, they could aid the search to discover and identify dark matter. They could also help solve the mystery of why black holes formed much faster than expected.
"Scientists think unseen, as-yet unidentified dark matter makes up about 95 percent of all matter in the universe. They know it exists because galaxies rotate faster than can be explained by the visible matter within them...."
This is a quibble, but that last paragraph isn't, quite, accurate - as far as I can tell. It's a fact: The visible parts of galaxies spin too fast, assuming that the stuff we see is all that's in the galaxies - and that gravity is all that's pulling the visible matter toward the center of the galaxy.
Dark matter is a pretty good working model to explain the odd behavior of stars and gas clouds in galaxies. And, it may actually exist.
Or, although this is getting more and more unlikely, dark matter may join phlogiston as a reasonable explanation for otherwise-unexplained phenomena - which turned out to be wrong.
The Space.com article discusses the possibility that the first stars were powered by the conversion of dark matter into energy. At this point, it looks like these "dark stars" wouldn't have radiated visible light - but would have emitted gamma rays, as the 2nd paragraph said.
Articles of this sort often use the phrase "dark matter" without trying to explain what it is. Can't say that I blame the writers and editors for that. It's easier to say what it isn't, than what it is.
Dark matter isn't ordinary stuff that's not illuminated. In other words, a rubber ball doesn't become "dark matter" when you put it in a drawer.
Princton's WordNet defines dark matter this way: Dark matter is "a hypothetical form of matter that is believed to make up 90 percent of the universe; it is invisible (does not absorb or emit light) and does not collide with atomic particles but exerts gravitational force".
Then there's dark energy - but that's another topic.
Dark Matter, Dark Stars, Stuff That's Billions of Years Old: So What?I'll admit that it's hard to see how pushing the envelope of knowledge about dark matter will make a difference in whether or not the New Orleans Saints make it to the Super Bowl this year.
Or keep the sidewalks shoveled this winter.
On the other hand, right now I'm using practical applications of wave and particle physics to write this blog.
Whether or not there turns out to be a practical application to research in physics and cosmology - and, eventually, I'm pretty sure there will be - I think there's value in the knowledge itself. It helps that I'm one of those people who is interested in the universe and how it works.
And, I'm glad there are resources like Space.com, where I can try to keep up with what's known, what scientists are discovering about how much they don't know, and observations that conform (or refute) established models to explain why things happen.