2010 Best NASA Photographs
Last December, The New Yorker published “The Best NASA Photographs of 2010.” Among these was a photograph of Abell 1689, a cluster galaxy that Yale astronomer Priyamvada Natarajan, Professor of Astronomy, helped produce. While this image itself is stunning, the photograph also represents a new observational method for studying dark matter and the geometry of the universe.
A galaxy cluster is a group of approximately 1000 galaxies held together by the gravitational force of dark matter. 90% of the mass of galaxy clusters are composed of dark matter, making them one of the largest repositories of dark matter in the universe. Abell 1689 is an unusually massive cluster – the dark matter’s gravitational pull is large enough to bend the visible light of background galaxies, as seen in the highly distorted galaxies in the center of the photo. This effect is known as gravitational lensing.
By measuring this distortion, Natarajan and her collaborators were able to calculate the mass of dark matter, as shown by the blue haze in the photo, and simultaneously constrain the geometry of the universe.
This is the first study of its kind to calculate both the geometry and mass content of the universe. As noted by Natarajan, “the larger finding of the work is yes, our universe is dominated by dark energy, so as a result, the universe is expanding and accelerating.” Natarajan plans to apply this technique to study other galaxy clusters to see if the results found are consistent with previously studied values for the fate of the universe.