Research: Atacama Cosmology Telescope

The Atacama Cosmology Telescope
The Atacama Cosmology Telescope.

Long before stars or galaxies had formed, the universe was a hot, dense gas that glowed at a few thousand degrees. Today, we can observe the light from this primordial glow, called the cosmic microwave background (CMB) radiation. Since it has come to us through a universe that has expanded in size by a factor of over a thousand, the wavelength of the light has been stretched from the visible part of the spectrum to the microwave—on the order of millimetres. Observations of the CMB over the past two decades have provided solid support for the Big Bang theory while also yielding a surprising amount of information about the early universe and about the make-up of the universe on its largest scales. On small scales, the CMB not only bears a record of the early universe, but also of the more recent universe, since its light has passed through clusters of galaxies and other large structures which leave their own distinctive imprints on the primordial signal.

The Atacama Cosmology Telescope (ACT) is a six-metre telescope on Cerro Toco, in the mountainous desert of northern Chile, dedicated to making high-resolution measurements of the CMB. Observations made with ACT from 2007 to 2010 have made significant contributions to our understanding of cosmology. We have made precise and detailed maps of the CMB which have contributed to tightening the precision on many of the fundamental parameters that characterise the universe, such as the running of the spectral index, the number of neutrinos and the amount of primordial helium, and have placed constraints on the state of the very early universe. We were the first group to detect gravitational lensing of the CMB by intervening cosmic structure, to provide evidence for dark energy using only the CMB and statistically to measure the motion of galaxy clusters relative to the expansion of the universe via the kinematic Sunyaev-Zeldovich effect. We have detected many clusters of galaxies (including a remarkably huge one) and done numerous follow-up studies of their properties. We have measured the microwave brightnesses of distant point sources and determined some of their important statistical properties.

The ACT collaboration hopes to add to these achievements with a major upgrade of the telescope's camera. This new receiver, ACTpol, was installed on the telescope in the austral winter of 2013. It is not only significantly more sensitive than the original receiver, but it is also capable of measuring polarisation of the CMB. These new features will make the telescope even better at measuring the properties of the early universe. ACTpol should be capable of measuring the number of neutrino species that were present in the early universe and continue the search for new galaxy clusters. It will be an excellent instrument for measuring the lensing of the CMB by cosmic structure, which can help us better understand the nature of dark energy.

External Links of Interest