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The Nature of Dark Matter

In general, scientists learn about the Universe by the electromagnetic radiation (or light) that we see from it. The light we see is in the form of radio waves, infrared, optical, ultraviolet, X-ray, and gamma-ray emission. But what if there is material in the Universe that does not glow? How will we ever know it is there? How can we tell how much of it there is? How do we know what it is?

Coma Cluster
Coma Cluster

Such material is called "dark matter" and astronomers now believe that most of the material in the Universe is made of this stuff. It is material that does not emit sufficient light for us to directly detect it; yet there are a variety of ways that we can indirectly detect it. The most common method involves the fact that the dark matter has a gravitational pull on the light and sources of light that we can see. From the effects of "extra" gravity that we detect, we infer how much mass must be present.

The kinds of materials that we experience every day are made of atoms, which are made of protons, neutrons, and electrons. We refer to this type of matter as "baryonic". Is the dark matter in the Universe made of the same stuff that we are familiar with, i.e. is it baryonic? Or is it something strange ...some kind of exotic new material, which we could call non-baryonic?

So far, it looks like there is both a kind of baryonic and non-baryonic dark matter, and it appears to be that the Universe is composed of both kinds. In fact, it is likely that most of the matter in the Universe is of some mysterious form that we cannot yet even identify!

The image at the left is of the Coma Cluster. It consists of two superimposed images: the red image is an Einstein satellite X-ray image; the blue image is a Palomar Sky Survey optical image. Scientists have used these observations to determine that the gravitational potential required to explain the observations implies a significant amount of "missing mass."

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Nicholas White (Director), within the Exploration of the Universe Division (EUD) at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Jim Lochner
Curator:Meredith Bene
Responsible NASA Official:Phil Newman
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