Universe Dark Energy-1 Expanding Universe. This diagram shows changes in the rate of expansion since the Universe's birth 14 billion years ago. The more shallow the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago, when objects in the Universe began flying apart at a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark energy that is pulling galaxies apart. Credit: NASA/STSci/Ann Feild
Perseus Cluster Dwarf Galaxies - These four dwarf galaxies are part of a census of small galaxies in the tumultuous heart of the nearby Perseus galaxy cluster. The galaxies appear smooth and symmetrical, suggesting that they have not been tidally disrupted by the pull of gravity in the dense cluster environment. Larger galaxies around them, however, are being ripped apart by the gravitational tug of other galaxies.
A Clash of Clusters Provides New Clue to Dark Matter A powerful collision of galaxy clusters has been captured by NASA’s Hubble Space Telescope and Chandra X-ray Observatory. The observations of the cluster known as MACS J0025.4-1222 indicate that a titanic collision has separated the dark from ordinary matter and provide an independent confirmation of a similar effect detected previously in a target dubbed the Bullet Cluster. These new results show that the Bullet Cluster is not an anomalous case.