Cosmological Applications of Gravitational Lensing

Stanford University, Stanford CA

Investigators

Abstract

A gravitational lens is produced when the gravitational field of a star, galaxy or cluster of galaxies distorts the images of background sources, 'strongly' when multiple images are created and 'weakly' otherwise. Gravitational lenses are now regarded as tools used to: (i) probe the nature of unseen mass, from black holes to dark matter and dark energy; (ii) measure distances and probe the size, shape and expansion of the universe; and (iii) study distant sources in exquisite detail. Future projects using new telescopes, like the Large Synoptic Survey Telescope and the SuperNova Acceleration Probe, will enable detailed, statistical studies of dark matter, and will provide a sensitive and robust measurement of the empirical behavior of dark energy. Past results from Dr. Blandford's group include: (i) demonstrating that dark matter is effectively collisionless and distinct from normal, baryonic matter (ii) a competitively accurate determination of the Hubble constant using a quadruply-imaged variable galaxy nucleus, (iii) measurement of the clustering of the faintest galaxies observed by the Hubble Space Telescope, (iv) understanding the distribution and clustering of distant quasars, and (v) developing new computational tools for cosmological investigations. The new work will include: (i) more detailed planning for handling the variability data for many thousands of lensed quasars, (ii) analyzing what can be learned from the rare lensed supernovae and gamma ray bursts, (iii) more about galaxy-galaxy weak lensing and what can be learned about the potential wells of galaxies and their halos, (iv) new ideas on systematic errors in gravitational lensing, notably the difficulty of distinguishing a change in the size of the universe from the addition of extra mass, (v) studying the predicted incidence of exceptional lenses that can be used to test the theory of how mass clumps in the expanding universe, (vi) the distribution of sizes of the largest gravitational lenses, and (vii) how to use the gravitational lensing-induced distortion of the clustering of faint galaxies to determine the distribution in space, properties, and histories of these galaxies. It will significantly advance understanding of the size, shape and expansion of the Universe and of the properties of its major constituents, dark matter and dark energy. Cosmological questions continue to attract much genuine interest among non-scientists and especially among young people who might ultimately become practicing scientists or engineers. Future projects with large publicly-accessible databases are likely to transform the relationship between professional and amateur astronomers.