|What is dark matter and how does it react to
|Question Date: 2009-02-26|
We don't know what dark matter is. That is the
very strange thing about it! We can detect it only
by its gravitational effect on other objects in
space. For example: dark matter seems to be
present in the halos of galaxies, causing the
rotation rates on the outer edges of the disks to
be constant instead of decreasing, as we observe
for the outer planets in the solar system. It
appears to be in between galaxies, and acts as a
gravitational lens, distorting the images of
distant galaxies similar to the way things look
distorted if you look through a wine glass which
isfilled with water. Dark matter does not interact
with normal matter, whichmakes it really hard to
find! But we think that dark matter particles
arestreaming through the earth all the time!
People are trying to find it by putting detectors
deep in mines. If a dark matter particle hits a
proton,there should be a transfer of momentum
which should temporarily cause the proton to spin
differently. So far, though, none have been
Here's a good website
to start reading more about dark matter:
is written by Martin White, a professor at UC
Berkeley, and an expert in this subject.
Dark matter is a type of matter that scientists
think exists in the universe, but aren't totally
sure yet. The reason why it's called "dark"
matter is because no one has seen dark matter yet
- we're pretty unsure what it is. Astronomers
have many ideas for what dark matter could be,
and many of those ideas think dark matter could be
a new form of matter, unlike electrons, protons,
and neutrons. However, these hypotheses are
unproven at this point.
So how to scientists
know that dark matter exists? When astronomers
look out into the universe, they can see the
affect matter has on other matter by looking at
how they interact through gravity. When looking
at many places in the universe, scientists see the
effects of gravity, but can't "see" all of the
actual matter that is causing the gravitational
effects. This is dark matter. As far as we can
tell right now, dark matter only interacts with
other matter through gravity.
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