The first robust evidence for the accelerated expansion of the universe (which led to the Nobel Prize in Physics 2011) was obtained using Type Ia Supernoave as “standard candles”. Most recently, new results may help using these fantastic events as even more effective distance indicators.
Through the observations of the fluctuations of the cosmic microwave background (CMB), we know that the universe curvature on large scales is approximately zero. This means that the average density of the universe is close to the so called critical value, benchmarking its future between a final collapse or eternal expansion. On the other hand, considering only the matter content of the universe, in both barionic and dark matter forms, it is only possible to account for about 30% the expected mass-energy content of the universe necessary to reach the critical density. This means that an extra 70% content is needed, which cosmologists refer to as “dark energy”. This conclusion is consistent with the observation of a dark energy driven accelerating expansion of the Universe. The first robust evidence for the accelerated expansion of the universe (which led to the Nobel Prize in Physics 2011) was obtained using Type Ia Supernovae, the thermonuclear explosion and of a white-dwarf in a binary system causing its destruction, as standard candles, through the co called “Phillips relation“ between the width and peak of Type Ia Supernovae lightcurves, to measure the distance of far away galaxies. It was then possible to establish that the expansion rate has increased over time under the influence of dark energy.
New exciting results
In order to best estimate their peak magnitude, most observers study SN Ia when they are young and at their brightest. Graur et al. 2020 presented results from late-time observations of SN Ia with the Hubble Space Telescope, which reveal that “normal” Type Ia Supernovae undergo a year-long plateau between 150 and 500 days past maximum light. The properties of the plateau provide not only a fresh diagnostic of Type Ia Supernovae explosion physics, but also a potential correlation between their intrinsic luminosity and their average infrared magnitudes on the plateau, which may significantly enhance their use as as standard candles and needs to be confirmed by further observations.
This picture may however be complicated by the the strong viewing angle dependence arising for certain explosion mechanisms (as found sub-Chandrasekhar double-detonation explosions by Gronow et al. 2020) which could lie off the “Phillips relation“, affecting their use as standardizable candles. Therefore, it is essential to clean the template sample of standard Type Ia Supernovae to reduce the dispersion and improve their usage as distance indicators. This means that having an accurate estimation of the Type Ia Supernova rate from different progenitors is essential.
References
Graur et al. 2020; Nature Astronomy, Volume 4, p. 188-195
Gronow et al. 2020; Astronomy & Astrophysics, Volume 635, id.A169, 17 pp.
