It appears the most of the matter in the Universe is non-luminous, IE not part of...

It appears the most of the matter in the Universe is non-luminous, IE not part of stars.

a) Describe the experimental evidence for the existence of this dark matter.

b) What is this dark matter made of, according to current thinking?

Expert Solution

Part A:

How do we know Dark Matter exists?

First part in a series of four on Dark Matter

Some of you may have heard of dark matter, this mysterious type of matter that no one can see but makes 27% of the content of the Universe while visible matter (you, me, all stars and galaxies) accounts for only 5%. How do we know it really exists? In fact, its existence is confirmed in many different ways.

Galactic clusters

Fritz Zwicky, a Swiss astronomer, was the first to suspect the existence of dark matter in 1933. He was trying to measure the mass of a galactic cluster (a group of several galaxies) using two different methods. He tried to infer this mass from the speed of the galaxies. Just like kids on a merry-go-round have to hold on to avoid being ejected, galaxies are held together in a spinning galactic cluster by the gravitational force provided by the matter it contains. If there were not enough matter to create this force, the galaxies would simply scatter.

He then compared his result with the mass evaluated from the light the galaxies shed. He realised that there was way more matter in the cluster than what was visible. This matter of an unknown type generated a gravitational field without emitting light. Hence its name, dark matter.

Velocity curves of spinning galaxies

But it was not until the 1970

genius_generous answered 1 year ago

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