August 30 - By observing the collision of two distant galaxies, scientists say that they now have direct evidence of dark matter's existence. For decades scientists have proposed the existence of dark matter as an explanation for how galaxies rotate at their observed velocities.
Dark matter emits no light and can only be detected by how it interacts with ordinary matter through gravity. One of the ways dark matter can be detected is by a phenomenon called gravitational lensing, which occurs when an object's gravitational field distorts light from background galaxies. However, dark matter is often embedded in galaxies, making it difficult to isolate the lensing it causes.
Researchers were able to directly detect dark matter by observing the collision between an enormous cluster of galaxies and a smaller galaxy cluster more than 3 billion light years away. The team reasoned that when the galaxies hit each other, the vast volumes of gas in each would slow down, but the dark matter would continue to speed along. Images from NASA's Chandra X-ray Observatory, the Hubble Space Telescope, and other instruments showed gravitational lensing in an area where there was no visible matter, indicating the presence of dark matter.
There are several National Research Council reports dealing with dark matter. Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century examines 11 questions that need to be and can be answered in the next decade, including "what is the nature of dark matter and energy." Astronomy and Astrophysics in the New Millennium recommends further research into dark matter and into developing dark matter detectors. Revealing the Hidden Nature of Space and Time: Charting the Course for Elementary Particle Physics affirms how particle physics research is necessary to maintain the United States' position as a scientific world leader and recommends several frontiers for further research, including dark matter.
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