The Universe’s Oldest Supernovae Burn Bright & Blue

The color of supernovae during a specific phase could help researchers detect the most distant and oldest supernovae in the Universe.

AsianScientist (Jul. 19, 2016) – Observing the color of supernovae during a specific phase may help researchers detect the most distant and oldest supernovae in the Universe, according to a study that has been published in The Astrophysical Journal.

For a hundred million years after the Big Bang, the Universe was dark and filled with hydrogen and helium. Then, the first stars appeared, and heavier elements were created by thermonuclear fusion reactions within stars. These metals were spread around the galaxies by supernova explosions.

Studying first-generation supernovae provides a glimpse into what the Universe looked like when the first stars, galaxies, and supermassive black holes formed, but to date it has been difficult to distinguish a first-generation supernova from an ordinary supernova.

Led by Dr. Alexey Tolstov from the Kavli Institute for the Physics and Mathematics of the Universe in Japan, the researchers identified characteristic changes between these supernovae types after experimenting with supernovae models. Based on metal-poor stars, or stars with virtually no metals, these models make good candidates because they preserve their chemical abundance at the time of their formation.

Similar to all supernovae, the luminosity of metal-poor supernovae show a characteristic rise to a peak brightness followed by a decline. The phenomenon starts when a star explodes with a bright flash, caused by a shock wave emerging from the surface of the progenitor stars after the core collapse phase. This shock breakout is followed by a long ‘plateau’ phase of almost constant luminosity, lasting several months, before a slow exponential decay.

The team calculated the light curves of metal-poor supernova produced by blue supergiant stars and metal-rich supernova produced by red supergiant stars. Both the shock breakout and ‘plateau’ phases are shorter, ‘bluer,’ and fainter for metal-poor supernovae in comparison with metal-rich supernovae. The team concluded that the color blue could be used as an indicator of a metal-poor, first-generation star.

“The explosions of the first generation of stars have a great impact on subsequent star and galaxy formation. But first, we need a better understanding of how these explosions look like to discover this phenomenon in the near future,” said Tolstov.

“The most difficult thing here is the construction of reliable models based on our current studies and observations. Finding the photometric characteristics of metal-poor supernovae, I am very happy to make one more step to our understanding of the early Universe.”

The article can be found at: Tolstove et al. (2016) Multicolor Light Curve Simulations of Population III Core-Collapse Supernovae: From Shock Breakout to 56Co Decay.

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