LQ13028 - A team of astronomers and physicists have for the first time detected motions
of galaxy clusters, the largest objects in the universe. In 1972, Rashid Sunyaev and
Yakov Zel'dovich predicted that a moving cluster of galaxies should slightly
shift the temperature of microwave background radiation passing
through it, in analogy with a Doppler shift. This effect has now been
observed statistically by combining a catalog of 27000 luminous galaxies
from the Sloan Digital Sky Survey's Baryon Oscillation Spectroscopic
Survey (which trace cluster locations on the sky) with overlapping
maps of the microwave background temperature from the Atacama
Cosmology Telescope. The collaboration finds that pairs of galaxy
clusters are slightly more likely to be moving towards each other
rather than away from each other, as expected from the attractive
nature of the gravitational force. This is the first direct measurement
of motions of objects at cosmological distances. Future improvements
of this measurement can give precisely characterize the growth of
structure in the universe and the nature of dark energy. The result also
demonstrates the power of combining large astronomical surveys,
allowing new statistical measurements of subtle physical effects that no
single survey could detect.
