Probing inhomogeneous cosmological models with supernovae

by Michael Blomqvist (Dept. of Astronomy, Stockholm University)

Friday 4 Jun 2010, 10:30 → 12:00 Europe/Stockholm

FA 31

Using type Ia supernovae as distance indicators to determine the expansion history of the universe has been a key component in establishing that the cosmic expansion is in a phase of acceleration. A plethora of cosmological models have been proposed to explain the apparent late-time acceleration, including models that predict spatial variations of dark energy, and models with large-scale matter inhomogeneities. One way to probe these types of models is to use the supernova positions in the sky to look for anisotropies in the redshift-magnitude diagram. In the first part of the talk I will present how we can use supernovae to probe dark energy inhomogeneities. The presence of such inhomogeneities along the line of sight will induce correlated fluctuations in the observed peak magnitudes of supernovae. Using the current supernova data it is not possible to rule out any phenomenological model with density fluctuations in the linear regime, but the method can be important in the future when data becomes more abundant. In the second part of the talk I will discuss a scenario in which we live within a large, spherically symmetric void in the matter distribution. Combining the supernova data with the observed dipole anisotropy of the cosmic microwave background, we find that the data compels the observer to be located within about one percent of the void scale radius, strongly disfavouring the model from a Copernican principle point of view.