Where the Universe Came From by New Scientist

Author:New Scientist
Language: eng
Format: epub
Publisher: John Murray Learning. An Hachette UK company.
Published: 2017-01-31T16:00:00+00:00

FIGURE 6.1 Evidence for dark matter: stars near the edge of galaxies are travelling too fast to be held in orbit merely by the gravity of the matter we can see in the galactic centre

Zwicky’s puzzling results drew little attention until the late 1960s, when Vera Rubin (1928–) at the Carnegie Institution in Washington DC measured the Doppler shift of clouds of hydrogen gas in several distant galaxies. This showed that the speeds at which the clouds were orbiting the centre of their galaxies seemed to require far more mass than could be accounted for by visible material.

Without dark matter, the very existence of many apparently stable galaxies would defy the laws of physics. The fact that they do exist remains among the most compelling reasons to think that there must be more to the cosmos than meets the eye.

The cosmic microwave background

Although we still cannot see the stuff itself, we see evidence for dark matter everywhere we look, for example in the radiation known as the cosmic microwave background (CMB). By studying the patterns of slightly hotter and colder patches in the CMB, we have been able to learn a great deal about our universe’s history and composition (see Figure 6.2). Among other things, these variations in the CMB tell us how matter was distributed throughout space in the early universe. Because dark matter began clumping under the influence of gravity earlier than normal matter did, its influence can be seen in numerous small hot and cold patches, each covering an angle in the sky of 0.25 degrees or so.

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