Speaker
Dr
Nicholas Kaiser
(Institute for Astronomy, U. Hawaii)
Description
Wojtak, Hansen and Hjorth (Nature, 2011) have measured the long-predicted
gravitational redshifts in galaxy clusters using Sloan Digital Sky
Survey data. The effect is very small, corresponding to a velocity shift
of only ~10 km/s in clusters with internal random motions ~600 km/s) but
is in good agreement with general relativity predictions and possibly in
conflict with some alternative gravity theories. Zhao, Peacock and Li
(2012) showed there should also be a competing special relativistic
effect - the transverse Doppler (TD) effect - of similar magnitude.
In this talk I will describe how there are two more kinematic effects
that need to be considered in interpreting these observations; a `light
cone' effect that augments the TD shift and a competing effect caused by
modulation of the surface brightness of galaxies by relativistic beaming.
I will discuss how these observations constrain gravitation theory.
Primary author
Dr
Nicholas Kaiser
(Institute for Astronomy, U. Hawaii)
