• Renée Hlozek (U. Toronto)  - hlozek at dunlap dot utoronto dot ca
  • Rahul Biswas (Stockholm University) rbiswas4 at gmail dot com

Observations of nearby and distant type Ia supernovae (SNe Ia) led to the discovery of the accelerating Universe driven by dark energy (Riess et al. 1998; Perlmutter et al. 1999). SNe Ia have played a starring role in the current renaissance of time-domain astrophysics that will reach a new apex with LSST. SNe Ia discovered by LSST will provide important new insight into dark energy, not only through improvements in the precision of constraints on dark energy parameters (w, wa , etc.), but also through novel tests of dark energy models (its isotropy, for example).

SNe Ia are exploding stars defined by the lack of hydrogen and the presence of silicon in their emission, and are the product of the thermonuclear explosion of a C/O white dwarf (Hillebrandt & Niemeyer 2000). The brightening and fading of a SNe Ia are observed through its photon flux at different dates and wavelengths, i.e., multi-band light curves. The luminosity at peak brightness can be predicted to ∼ 12% accuracy from light-curve shapes and colors. The ratio between the observed flux and predicted luminosity at peak brightness is a measure of the object’s luminosity distance. An accurate redshift is typically obtained from the host galaxy, although it can be obtained from the supernova itself.

As “standardizable candles”, SNe Ia map the expansion history of the Universe through measurements of their redshifts and luminosity distances. The SN Ia Hubble diagram is compared to cosmological models to measure the parameters that determine the dynamical evolution of the Universe. The redshift range of SNe Ia discovered by LSST, 0.1 < z < 1.2, spans eras of both cosmic acceleration and deceleration, and the transition between the two. SNe Ia are therefore excellent probes of the physical properties of the dark energy responsible for the accelerated expansion of the Universe.

(Image Credit: STSci)


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