Dr. Michael Brotherton, Ph.D.

Associate Professor, Department of Physics & Astronomy

University of Wyoming

Refreshments at 3:15 P.M.

Title and Abstract: Quasar Doppelgangers and the Implications for Cosmology

Quasars, the accreting supermassive black holes at the centers of galaxies, are the most luminous objects in the universe and in principle ideal for use as so-called "standard candles" to help unravel the nature of dark energy. Despite possessing a number of spectral features long known to correlate with luminosity, quasars have failed to become useful as standard candles. We have employed statistical techniques to identify quasars with virtually identical spectra, which we call doppelgangers, in order to understand the limits of determining luminosity from spectral features alone. While the majority of doppelgangers have very similar luminosity, there exists a surprisingly large scatter. We offer some possible physical explanations for this large variance and their implications for cosmological application.