Supernovae found by SDSS-II

A mosaic showing 36 of the the 500+ Type Ia supernovae discovered by the Sloan Supernova Survey. Each image is centered on the supernova, which usually stands out as a bright point near or within the galaxy that hosts it. The light of the supernova, powered by the thermonuclear explosion of a single white dwarf star, can outshine that of the tens of billions of stars in its host galaxy. Type Ia supernovae have a constant intrinsic luminosity (after a correction based on the time over which their light rises and falls), so their apparent brightness can be used to infer their distance. The primary goal of the Sloan Supernova Survey was to measure the expansion of the universe with high precision over the last four billion years of cosmic history, to help understand why that expansion is speeding up over time despite the decelerating gravitational effect of atoms and dark matter.
Credit: B. Dilday and the Sloan Digital Sky Survey.