 Caltech-NRAO team which he led showed in 1997 that gamma-ray bursts came from extra-galactic sources, and identified optical counterparts.Their research initiated the detailed studies of the sources of gamma-ray bursts along with the European team led by Jan van Paradijs.He was also a member of the Caltech team that observed the first irrefutable brown dwarf in 1994 that orbited around a star called Gliese 229.