Dark Matter - What is it?

The Bullet Cluster: Empirical Evidence for Dark Matter

This structure is two clusters of galaxies passing through one another. As the two clusters cross at a speed of 10 million miles per hour, the luminous matter in each cluster interacts with the luminous matter in the other cluster and slows down. But the dark matter in each cluster does not interact at all, passing right through without disruption. This difference in interaction causes the dark matter to sail ahead of the luminous matter, separating each cluster into two components: dark matter in the lead and luminous matter lagging behind. In 2006, Marusa Bradac, a postdoctoral fellow at KIPAC, and her colleagues made the landmark observations by studying a galaxy cluster 3 billion light years away.

Only about five percent of the total matter + energy content of the Universe is familiar to us. The identity of the remaining 95 percent, roughly 1/3 of it dubbed as "dark matter" and roughly 2/3, dubbed as  "dark energy" is unknown. Though scientists have not yet detected it directly in laboratories on Earth, dark matter’s existence has been deduced from its gravitational effects on the stars and gasses that make up all of the galaxies known in the Universe.

Dark Matter's Crucial Role

In addition to its physical effects, dark matter is a crucial component of the cosmological theory because of its key role in defining the structure of the universe and in binding all galaxies – even our own Milky Way – together. Modern astrophysics and particle physics theory suggests that dark matter exists in the form of a yet undiscovered elementary particle.

Dark Matter is Everywhere

Dark matter is pervasive throughout the Universe – so it’s no surprise that dark matter is also prevalent on Earth. Based on observations of the motions of nearby stars, theory predicts that one dark matter particle will inhabit a volume the size of your coffee cup. The direct identification of the nature of dark matter will establish a firm connection between physics on the largest astronomical scales and the smallest scales studied in laboratories on Earth.

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