References and Links
Contents
What is Dark Matter?
Not too long ago, astrophysicists noticed that the outtermost parts of galaxies were rotating much faster than they should be. After adding up all of the mass of the stars and dust, there simply wasn't enough mass to hold the galaxies together. Since we don't see galaxies flying apart, there must be more matter in them (somewhere between the stars) than is visible. This extra "missing" matter is called dark matter . It's referred to as "dark" because it doesn't emit light that we can detect (unlike stars).
Who Cares?
Cosmologists do. A large amount of missing matter in the universe directly affects measurements of many of the cosmological parameters and our knowledge of the fate of the universe. In fact, dark matter may have been responsible for the original formation of galaxies and stars. To make things even more interesting, dark matter may be composed of a new type of particle predicted by Grand Unified Theories, making it the key to understanding not only one of the biggest mysteries in cosmology, but also in particle physics.
Dark Matter Candidates:
- MACHOS
- (Massive Compact Halo Objects) These are big
dark objects like brown dwarf stars, white dwarfs, neutron stars, and
black holes. So far, it doesn't look like this can be anywhere near
the whole story.
- WIMPS
- (Weakly Interacting Massive Particles) These
are various non-baryonic subatomic particles believed to be created in
the Big Bang. Many particle theories predict the existence of WIMPS
such as neutralinos, axions, and massive neutrinos, but none have
actually been detected. If they do exist, then there is a good
possibility that the dark matter is made up of them.
- MASSIVE NEUTRINOS
- These are predicted due to the
difficulty of getting galaxy formation models to work since neutrinos
would wash out the initial "seed" density perturbation.
Where do we fit in?
Of of the goals of the VERITAS project is to try and detect gamma rays that are coming from neutralinos annihilating in our galactic core (the presence of a centrally cusped density profile is predicted by recent structure formation models). These annihilations should create an observable signal in an energy range of neutralino's mass (which is theoretically between ~30GeV to a few TeV). If this effect is detected, then it not only shows that neutralinos exist, but that they make up at least some of the dark matter in our own galaxy. Furthermore, this should be possible to observe with a 10m atmospheric Cherenkov telescope such as Whipple , if the energy threshold can be reduced. Such a threshold will be met through the use of FADC and CFD electronics and better photon detectors all being developed here at Washington University. Future detectors such as VERITAS and HESS will be sensitive to a large fraction of parameter space.
hbar.wustl.edu>
