Dark matter

It was an old idea of Stephen Hawking’s: Unseen “primordial” black holes might be the hidden dark matter. A new series of studies has shown how the theory can work.

Cosmologists have concluded that the universe doesn’t appear to clump as much as it should. Could both of cosmology’s big puzzles share a single fix?

Modified gravity theories have never been able to describe the universe’s first light. A new formulation does.

Researchers say there are three possible explanations for the anomalous data. One is mundane. Two would revolutionize physics.

Physicists have proposed extra cosmic ingredients that could explain the faster-than-expected expansion of space.

In a new paper, physicists argue that hypothetical particles called axions could explain why the universe isn’t empty.

A photograph of the infant cosmos reveals the precise amounts of dark matter and dark energy in the universe, leaving precious little room for argument.

Physicists have long searched for hypothesized dark matter particles called WIMPs. Now, focus may be shifting to the axion — an ultra-lightweight particle whose existence would solve two mysteries at once.

Most every cosmologist believes the universe is flat. A new analysis argues that it’s closed.