What the heck is dark matter?
Dark matter is another one of those enigmatic things that cosmologists argue about. It's probably some unknown quantum particle that no one can find; although, lots of scientists are trying to do just that.
At this point in time, dark matter is only hypothetical. It's been proposed to explain the missing matter in the universe. Matter that we can see out there in the universe only accounts for 4.9 percent of the total mass and energy. Remember that matter and energy are interchangeable according to Einstein. Without dark matter, the galaxies would be flying apart, despite the fact that most galaxies have a super massive black hole in their centers. We here on Earth would be flying away from the Milky Way if it weren't for dark matter. The fact is that dark matter makes up 26.8 percent of the total matter and energy of the universe. That's a lot for something we can't see!
But what the heck is it? That's a question that quantum physicists and cosmologists are trying like the devil to answer. Let's be clear about one thing: dark matter's existence has been proven by observation. We just don't know what the heck it is. One thing we do know is that it's not Baryonic matter. What the heck is that? Baryonic matter contains protons, neutrons and electrons like normal matter. Some dark matter may be Baryonic and be hiding in dark objects, but such matter only makes up a tiny fraction of total dark matter.
If dark matter is nonbaryonic then what would it be composed of? That's another good question. Possible things it could be consist of hypothetical quantum particles like axions or supersymettrical particles like neutrinos, but neutrinos are too light to be dark matter. Three types of exotic matter could be fit the bill: cold dark matter, warm dark matter and hot dark matter. This sounds like the porridge in the Goldilocks and the Three Bears fairy tale. Most quantum physicists like cold dark matter, and the best candidate is a WIMP or weakly interactive massive particle. The reason why it's considered weakly interactive is because it seems to be so hard to find. It passes through Earth and us without interacting with our atoms.
This reminds me of Aerosmith's 'Come Together' -- Got to be good lookin' 'cause he's so hard to see.
Most of the proof for the existence of dark matter comes from observing the light to mass ratio of galaxies and their motion. The amount of light coming from a given galaxy just doesn't add up to the mass needed to hold the galaxy together. Also, the attraction of one galaxy for another, such as the Milky Way's attraction to Andromeda, is impossible without much more matter than what we can see. Another proof is called gravitational lensing. The Hubble space telescope discovered this when pictures it took of galaxy clusters revealed distorted images of distant galaxies billions of light years away. The galaxy cluster was acting like a giant lens, magnifying these distant galaxies. This effect required much more matter than the visible light from the galaxy cluster suggested it had.
So far the best candidate for dark matter is the WIMP. A WIMP particle would be slow moving and therefore cold. It would be more massive than standard particles and because of slow motions would clump together with other dark matter particles.
Attempts to detect these particles have resulted in failures; although in 2010 the Cryogenic Dark Matter Search detector at Soudan Mine detected two events that could be by WIMP collisions with the detector. If the data can be verified it could mean that science has detected the elusive dark matter particle. Now it's on to the very mysterious dark energy!
Thanks for reading.