Robert P. Kirshner
Harvard-Smithsonian Center for Astrophysics
Election Year: 1998
Primary Section: 12, Astronomy
Membership Type: Member
I am an observational astronomer who works on supernova explosions to measure the size and motion of the Universe. Careful measurements of spectra and light curves for supernovae make them the best tools for determining extragalactic distances. Comparing supernovae in galaxies near and far, we measure the age of the Universe (about 14 billion years give or take a billion) and detect the change in cosmic expansion during the past 8 billion years. Surprisingly, this change is not a slowing-down from the cumulative effects of gravitating matter, but an acceleration. This evidence points toward the existence of another major constituent of the Universe, a form of energy associated with the vacuum of space itself, that may resemble Einstein's cosmological constant. Studies of Supernova 1987A, the great supernova of our lifetime (so far!) in the Large Magellanic Cloud show that the expanding debris from this explosion are about to collide with the circumstellar gas to produce a new and violent stage in the evolution of this object. I have also been engaged in efforts to measure the distribution of galaxies in three dimensions through large redshift surveys. Early work led to the discovery of the Bootes Void, a nearly empty region 150 million light years across. More recent investigations include the Las Campanas Redshift Survey, whose 25,000 redshifts make it the largest completed survey.