Louis-Gregory Strolger
Space Telescope Science Institute
Supernovae and the Accelerating/Decelerating Universe

Observations of distant Type Ia Supernovae (SNe Ia) have astonishingly shown evidence that the Universe is accelerating, apparently driven
apart by a pervasive smooth cosmic tension, or ``dark energy''. However, it is possible that there are other astrophysical effects
which allow SNe Ia to seem systematically fainter with distance, therefore mimicking the most convincing evidence for the existence of
dark energy. A simple test of the dark energy result would be to observe SNe Ia at even higher redshifts than previously done. In the
redshift range of 1 < z < 2, we should observe SNe Ia entering an epoch  of cosmic deceleration, therefore appearing systematically brighter
than at lower redshifts; distinctly different than what is expected from conventional challenges (e. g. grey dust) to the dark energy
result. In co-operation with the Great Observatories Origins Deep Survey, we have used the Hubble Space Telescope to discover and follow
42 SNe, of which ~ 10 were SNe Ia at z > 1. I will present an overview of this deep supernova survey, and new constraints they impose on dark
energy and other cosmological parameters. I will also show new results based on the supernova rates that give insights on the progenitor
mechanisms which create Type Ia events.