HColloquium Seminar Announcement Prof. Alex Filippenko UC Berkeley " Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy" Date: Monday, February 14, 2005 55 Roessler Time: 4:10 pm. Abstract: The measured distances of type Ia (hydrogen-deficient) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of repulsive dark energy (X) such as Einstein's cosmological constant (Lambda). Combining all of the data with existing results from large-scale structure surveys, we find a best fit for Omega_M and Omega_X of 0.28 and 0.72 (respectively), in excellent agreement with the values (0.27 and 0.73) recently derived from WMAP measurements of the cosmic microwave background radiation. A number of possible systematic effects (dust, supernova evolution) thus far don't seem to eliminate the need for Omega_X > 0. Most recently, analyses of supernovae at z = 1.0-1.7 reveal an early epoch of deceleration, followed by acceleration. Several groups are now in the process of measuring hundreds of supernovae with z = 0.2-0.8, to determine the equation-of-state parameter of the dark energy, w_X = P/(rho c2). Thus far, the best-fit value is w_X = -1, and its first derivative is consistent with zero, suggesting that the dark energy may indeed be the cosmological constant or something quite similar.

Bio: Alex Filippenko received his B.A. in Physics from UC Santa Barbara in 1979, and his Ph.D. in Astronomy from Caltech in 1984. He then became a Miller Research Fellow at UC Berkeley, and he joined the Berkeley faculty in 1986. His primary areas of research are supernovae, active galaxies, black holes, gamma-ray bursts, and observational cosmology; he has also spearheaded efforts to develop robotic telescopes. He has coauthored over 450 publications on these topics, and has won numerous awards for his research, most recently a Guggenheim Fellowship. A dedicated and enthusiastic instructor, he has won the top teaching awards at UC Berkeley, and was four times voted the "Best Professor" on campus in informal student polls. In 1998 he produced a 40-lecture astronomy video course with The Teaching Company, and in 2003 he taped a 16-lecture update on recent astronomical discoveries. In 2000 he coauthored an award-winning introductory astronomy textbook; the second edition appeared in 2003.

E-Mail: alex@astron.berkeley.edu
Web Page: www.berkeley.edu