Type Ia Supernovae and Cosmology

Summary

Type Ia Supernovae (SNe Ia) provide cosmologists with a precise calibrateable “standard candle” with which to probe the expansion history of the universe on large scales. Pioneering astronomical surveys in the late 1990s exploited these distant cosmic explosions to directly reveal the presence of a “dark energy,” opposing the attractive, slowing force of gravity and instead accelerating the universe’s rate of expansion. Dark energy has since emerged as being responsible for more than 70% of the universe’s mass–energy: the lack of a viable theoretical explanation has sparked an intense observational effort to understand its nature. In this chapter we review the use of SNe Ia in cosmology and dark energy studies. We begin by placing the SNe Ia in a cosmological context, introducing the framework in which their physical fluxes are interpreted, and discussing their underlying physics which leads to their near-uniform peak brightness, exploited by astronomers to estimate distances. We show how advances in the empirical understanding of SNe Ia led to the direct discovery of the accelerating universe and how modern SN Ia searches and distance estimation techniques, combined with complementary probes of large-scale structure such as baryon acoustic oscillations, have measured the average equation of state of dark energy to better than 5% (statistical error). Systematics are now of increasing importance and we discuss the main sources of these, both experimental and astrophysical, together with an experimental error budget typical of that in a modern SN Ia survey. Finally, we outline the future prospects for measuring dark energy with SN Ia using the next generation of planned experiments.