Supernovae are the explosive deaths of stars. Since stars of different mass follow different evolutionary tracks they face different end stages, which gives rise to a large variety of luminosities and spectral features among the supernovae.
One special type of supernovae, Type Ia, appears to always explode with the same brightness, making them useful as distance indicators. The accelerated expansion of the Universe was discovered using SNe Ia, leading to Perlmutter, Schmidt & Riess being awarded the Nobel Prize in 2011. While the use of SNe Ia remains essential for the studying the properties of the “dark energy” driving this accelerated expansion, the lack of understanding of the SN progenitor systems and the empirically derived standardization corrections represent severe limitations for SNe Ia as cosmological probes.