Dark Matter

Dark Matter

Dark Matter is completely invisible. It does not interact with normal matter(the stuff we are made of), nor can we detect it. This strange form of matter makes up about 85% of the mass in the universe. We can imply its presence due to its force of gravity which cannot be accounted for by normal matter.

History of Dark Matter

In 1933, Swiss Astronomer Fred Zwicky was studying a far-off cluster of galaxies called the Coma Cluster. Based on Newton's laws he inferred that the observable mass in the cluster could not generate the angular momentum observed and the cluster should have drifted apart. However, this was not the case, so Fred Zwicky inferred a type of matter which he called dunkel Materie(Dark Matter). He estimated there was about 400 times as much mass in the cluster than what could be observed.

In the 1970s astronomer, Vera Rubin found similar problems in the Milky Way Galaxy. She noticed that the stars in the centre were revolving only slightly faster than the stars on the edge of the galaxy. This, was a violation of newton's laws unless there was a mass on the edges which drove this acceleration.

These problems made scientists infer the presence of an unknown, unreacting mass which dominated the universe. They called it Dark Matter.

Composition

Scientists have no idea what Dark Matter composes of. But they do have a decent idea of what it must not be:

1. Baryonic Matter: Baryonic matter is the matter you and I are made of, consisting of protons and neutrons. Dark Matter does not react with light like Baryonic matter and hence cannot be it.

2. Black holes: Black holes, due to their strong gravity do not allow light to escape, hence not allowing detection. But, Balck holes can be detected by their effect on stars in their vicinity. Therefore, Dark Matter must not be Black Holes.

Dark Matter may be composed of the following:

1. WIMPS(Weakly Interacting Massive Particles): These particles are believed to have about 10-100 times the mass of a proton. However, they interact very weakly with normal matter. Neutralinos, a hypothetical particle is the foremost on the list but is yet to be detected.

2. Sterile Neutrinos: Sterile neutrinos are another candidate. Neutrinos are particles that don't make up regular matter. A river of neutrinos streams from the sun, but because they rarely interact with normal matter, they pass through Earth and its inhabitants. There are three known types of neutrinos; a fourth, the sterile neutrino, is proposed as a dark matter candidate. The sterile neutrino would only interact with regular matter through gravity.