UCLADepartment of Physics & Astronomy Thursday April 22, 2004 at 3:30pm Room 1200

Alexei V. Filippenko, Professor of Astronomy University of California - Berkeley

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 Fellow at UC Berkeley, and he joined the Berkeley faculty in 1986. His primary areas of research are supernovae, active galaxies, black holes, and observationalcosmology; he has also spearheaded efforts to develop robotic telescopes. He has coauthored over 400 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 in 1995, 2001, and 2003 he was 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

b i o introductory astronomy textbook; the second edition appeared in 2003.

Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy

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 (L). Combining all of the data with existing results from large-scale structure surveys, we find a best fit for WM and WX 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

a b s t r c microwave background radiation. A number of possible systematic effects (dust, supernova evolution) thus far don't seem to eliminate the need for WX > 0. Most recently, analyses of supernovae at z = 1:0 – 1:7 reveal anearly 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 of the dark energy, wX = P=(pc2); thus Image courtesy of NASA/STScI/Ann Feild. far, the best-fit value is wX = –1, suggesting that the dark energy may indeed be the cosmological constant or something quite similar. Refreshments immediately following in room 2-222 designed by Mary Jo Robertson