Peter Nugent studies supernovae to answer basic questions about the nature and destiny of the Universe

An exploding star dubbed SN 1997ff, caught on three different occasions by NASA's Hubble Space Telescope, is the oldest and most distant Type Ia supernova ever seen, according to a recent analysis by Peter Nugent, one of NERSC's two staff astrophysicists. Peter is a member of the team led by Adam Riess at the Space Telescope Science Institute that studied the distant supernova.

The discovery of the more than 11-billion-year-old supernova is important for several reasons. This supernova is consistent with the cosmological model of an accelerating universe, a universe mostly filled with dark energy. It argues against the notion that observations of distant Type Ia supernovae may be systematically distorted by intervening gray dust or the chemical evolution of the universe. Moreover, the supernova is so ancient that it allows us to glimpse an era when matter in the universe was still relatively dense and expansion was still slowing under the influence of gravity. More recently the dark energy has begun to predominate and expansion has started to speed up.

The Supernova Cosmology Project and the High-Z Supernova Search Team, the two international groups of astronomers and physicists who discovered the accelerating expansion of the universe, use Type Ia supernovae as "standard candles" to measure cosmological parameters. Type Ia spectra and light curves (their rising and falling brightness over time) are all nearly alike, and they are bright enough to be seen at very great distances.

With a redshift (or z) of about 1.7, supernova 1997ff is some 11.3 billion years old, much older—and much fainter—than the previous record of z equals 1.2, which corresponds to an age of about 9.8 billion years old. A supernova at redshift 1.7 is too far away to have been visible from the surface of the Earth. Only a space-based telescope could have found it.

Peter is involved in two related supernova projects, one for accelerating the acquisition of data and one for analyzing the data. The first is the Nearby Supernova Factory, an international collaboration that aims to discover large numbers of Type Ia supernovae as soon as possible after they explode. In this project, raw images will be transferred to NERSC nightly from remote observatories; the images will be calibrated and corrected, then compared with baseline sky catalogs; automated search algorithms will then look for indications of supernova activity; and the results will be relayed back to the observatories so that more detailed observations can be made. This close interaction between observation and computation, involving huge datasets, requires high performance computers, storage systems, and Grid technologies. The Supernova Factory is an earth-based observation program that will serve as a development testbed for the next-generation search program, the satellite-based Supernova Acceleration Probe (SNAP).

Peter is also a leader of the Spectrum Synthesis of Supernovae project, which is analyzing data from both nearby and distant supernovae to measure the fundamental parameters of cosmology. One of this group's models, which used to take a few months to run, was completed in four days on NERSC's new IBM SP.