What is Dark Matter?

DARK-MATTER MAP. Gravitational lensing within galaxy cluster CL0025+1654, mapped by the Hubble Space Telescope, revealed an enormous halo of dark matter (in blue) must surround the brighter galaxies.

J.-P. Kneib/ESA/NASA

Astronomers might be more confident about their picture of the universe were it not for dark matter. Observations show that the universe is populated with some unseen form of matter — and plenty of it. Astronomers attempt to “weigh” the universe in a variety of ways. They observe the effects of dark matter on astronomical objects that vary from small to large.

Astronomy magazine subscribers can read the full article for free. Just make sure you're registered with the website.