Narrator (Megan Watzke, CXC): This composite image of the galaxy cluster Abell 3376 shows X-ray data from the Chandra X-ray Observatory and the ROSAT telescope along with an optical image from the Digitized Sky Survey and radio emission observed by the Very Large Array. The "bullet-like" appearance of the X-ray data is caused by a merger, as material flows into the galaxy cluster from the right side. Two different teams used Chandra observations of galaxy clusters, including Abell 3376, to study the properties of gravity on cosmic scales. This allowed them to test the Theory of General Relativity, and it turns out Einstein and his theory are still holding their own. Such studies are crucial for understanding the evolution of the universe, both in the past and the future, and for probing the nature of dark energy, one of the biggest mysteries in science.
Revised: May 10, 2010