Measurements in astronomy imply that up to 90% or more of the Universe is in the form
of "dark matter". This matter does not emit light or any other detectable
radiation, so we cannot "see" it, but its presence is felt through its
gravitational effects on the matter we can see. Stars in galaxies, for example, appear to
be moving much faster than they would if they were influenced only by the visible matter
in the galaxy.
 |
The gravitational lensing of a distant galaxy due to a foreground cluster of galaxies two billion light years away has allowed the reconstruction of the total mass of the foreground cluster and shows that the dark matter outweighs all the stars in the cluster's galaxies by 250 times. A false-color computer reconstruction of the dark matter mass per area in the cluster CL0024+1654, is here seen in projection. The total mass is over 300 million million million times the mass of the Earth. Individual galaxies in the cluster appear as mass pinnacles. (CREDIT: Greg Kochanski, Ian Dell'Antonio, and Tony Tyson - Bell Labs, Lucent Technologies). |
Some of the dark matter may be in the form of large planets or dead stars made from
ordinary protons and neutrons. However cosmological theories imply that a large fraction
of the dark matter must be of an entirely different form. Whatever its nature, it must be
very weakly interacting, otherwise it would already have been detected. One possibility is
that the weakly-interacting particles called neutrinos could have a small mass, and make
up dark matter, but the behaviour of neutrinos causes problem in theories of how galaxies
formed in the Universe.
Another possibility is that dark matter could be in the form of particles predicted by
theories, but not yet seen. The idea of "supersymmetry" links matter particles
with force-carrying particles, and implies the existence of heavy
"superparticles". The lightest of these superparticles could be stable, in which
case large numbers of them created in the early Universe could now have clustered into
structures of dark matter on the scale of galaxies.
© Copyright CERN - Last modified on 1998-02-19 - Tradotto da Sofia Sabatti