Description

Cosmology is the study of the large scale properties of the Universe as a whole. Cosmologists try to understand the origin, evolution and ultimate fate of the entire Universe. This involves the formulation of theories or hypotheses about the Universe which make specific predictions for phenomena that can be tested with observations. Some of the key open questions in cosmology are: what types of matter and energy fill the Universe? how rapidly is the Universe expanding today? how old is the Universe today? what is the shape of the Universe? how does the expansion of the Universe change with time? and what is the ultimate fate of the Universe?

There are many useful observational probes of the nature of our Universe, each of which constrains one or more particular aspects of the Big Bang model and our understanding of structure formation. Indeed, the current era is considered the golden age of cosmology as observations of supernovae, galaxies and clusters, the cosmic microwave background radiation and the abundance of light elements taken together strongly constrain the properties of our Universe. These observations suggest that our Universe is homogeneous on the largest scales, is expanding and accelerating, was hotter and denser in the past. The constituents of the Universe are atoms (4%), dark matter (23%), dark energy (73%). Thus 96% of the energy density in the Universe is in a form that has never been directly detected in the laboratory. The bulk of the matter in the Universe is dark matter, however the nature of the dark matter particle is as yet unknown. Similarly dark energy provides the repulsive force that causes the accelerated expansion of the Universe but its nature is also unknown. Cosmologists at Yale pursue research activities ranging from studies of the very early Universe, structure formation and evolution in the early and late Universe using active galactic nuclei, galaxies and supernovae as probes.

Group 1 - Priyamvada Natarajan

At Yale, Prof. Priya Natarajan, a theoretical cosmologist is involved in mapping dark matter and dark energy in Universe. She has devised methods that exploit the phenomenon of gravitational lensing in galaxy clusters to map the detailed distribution and clustering of dark matter. Results from these studies are in agreement with our current understanding that dark matter in the Universe is cold and collisionless. Pursuing clues to the nature of dark matter, she is also actively working on the astrophysical consequences of the self-annihilation of dark matter particles.

Prof. Natarajan is also interested in the formation of the first black holes in the Universe, their relation to galaxy formation, their subsequent growth and the observational signatures of these processes. Other topics in black hole physics that she works on include the structure of accretion disks that feed black holes and the spins of black holes. Details of her research interests, her research group, current projects and publications are available at Prof. Natarajan's home page.

Group 2 - Richard Easther

Prof. Richard Easther is a theoretical physicist, whose work explores the connections between modern ideas in particle physics and cosmology. His interests include the cosmological implications of string theory, and whether these lead to predictions for the overall form of the universe than can be tested with current or planned astrophysical observations. Prof. Easther is currently involved with a number of projects aimed at understanding the possible observational constraints on different models of the "inflationary epoch", a period around a trillion, trillion, trillionth of a second after the big bang when the expansion rate of the universe rapidly accelerates, and which is responsible for fixing many of the present day properties of the universe.

Group 3 - Meg Urry

Ultra-deep surveys of the Universe probe the formation and evolution of the first galaxies and the first black holes. Prof. Meg Urry and her group have been conducting large-area surveys toand probe the demographics of supermassive black holes, particularly obscured AGN not found in optical surveys, and the evolution of AGN with redshift. She played a key part in designing several such surveys, including MUSYC, GOODS, and COSMOS. Her group is now studying AGN found in these surveys, and their close connection to galaxies, in part through a detailed study of the host galaxies of AGN, their evolution and luminosity dependences, and the properties of black holes of all types.

Urrys group also works on blazars, which are radio-loud AGN whose relativistic jets are closely aligned with the line of sight. By studying their time variable spectral energy distributions, one can learn about jet physics, jet power, and blazar demographics. The imminent launch of GLAST will revolutionize these studies, and allow us to determine what distribution of jet powers nature produces. Many blazers have kiloparsec-scale extended X-ray jets, usually coincident with radio and optical counterparts. With data with Chandra, HST, and Spitzer, Urry's group studies the physics of such extended jets. If the emission is synchrotron radiation augmented by inverse Compton scattering, the kinetic power in the jet and its matter content can be determined.

Group 4 - Charles Baltay

Prof. Charles Baltay runs the Palomar/QUEST variability survey, which uses the QUEST-II wide-field imaging camera on the Samuel Oschin 1.2-m telescope on Mt. Palomar. QUEST has accumulated data from Palomar almost continually since July 2003, with about 15,000 total square degrees of sky surveyed to R ~ 21 at each of 10-15 epochs. Collaborators at Yale, Lawrence Berkeley National Laboratory (LBL) and Caltech mine the data set to search for a wide variety of rare and/or variable objects, including supernovae (both thermonuclear and core collapse), strong gravitational lens systems, active galactic nuclei, and new classes of transient sources.

The Yale Nearby Supernova Factory (SNfactory) group conducts photometric follow-up of SNe Ia discovered in the Palomar/QUEST survey, concentrating on SNe in the low-redshift Hubble flow (0.03 < z < 0.08). Follow-up facilities include the CTIO 1.3-m telescope (through the SMARTS consortium) and the Aristarchos 2.3-m telescope on Mt. Helmos (in collaboration with the National Observatory of Athens). Yale SNfactory collaborator have access to photometric and spectroscopic observations of Palomar/QUEST SNe Ia taken at the University of Hawaii 2.2-m telescope on Mauna Kea. Yale also participates in the SNAP collaboration, a proposed space experiment to study the properties of dark energy.