Dark matter in astronomy is the name give to an invisible
matter or substance of unknown composition, which is supposed to constitute more than
nine tenths of the total mass of galaxies and clusters of galaxies. This matter, unlike
all other matters or substances, does not give off, reflect, or absorb light. This is
the reason why it is called dark matter.
Scientists have
proposed different theories or hypothesis about the nature of the dark matter but there
none of theories is are considered to be satisfactory explanations of nature of dark
matter. The nature of dark matter is one of the most important unsolved mystery in
science today.
Dark matter should not be confused with
black holes which are collapsed objects, such as a stars, that have become invisible.
They has such a strong gravitational force that even light is pulled in by it. Black
holes are invisible because any light approaching them is pulled in by the gravitational
pull and no light can then escape away from it.
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