Physics Colloquium - To the Heart of the (Dark) Matter: Testing the Universality of the Dark Matter Distribution

Event Date: 

Tuesday, February 24, 2015 - 4:00pm

Event Location: 

  • Broida 1640

Event Contact: 


Drew Newman, The Carnegie Observatories


Cold dark matter is a cornerstone of the modern cosmological model and underpins our understanding of galaxy formation. Simulations that follow the gravitational collapse of dark matter have shown that the resulting objects—dark matter “halos”—obey a universal density profile that is nearly independent of scale. Observations of the dark matter distribution in halos of different masses provide an essential test of this prediction. I will describe an observational program focused on mapping the dark matter distribution in massive galaxy clusters, the largest collapsed halos. By combining methods such as gravitational lensing and stellar dynamics, we have measured the mass density profile over an unprecedented dynamic range in radial scale. Surprisingly the dark matter profile deviates from the “universal” form at small radii by following a shallower slope. This intriguing result points either to a “non-standard” dark matter particle or to a redistribution of dark matter during the formation and assembly of the central galaxy. I will review these possibilities and describe how we can begin to discriminate amongst them. Finally, I will conclude with a brief overview of future observations that will allow us to probe dark matter in lower-mass systems and to better isolate the dark and luminous components of galaxies.