Red supergiant supernova gives astronomers new insights into the make-up of the early universe

Images showing a red supergiant star exploding – going supernova – more than 11 billion years ago, could help scientists learn more about the early universe.

Researchers at the University of Minnesota Twin Cities in the US have measured the size of the star from images made up of light that travelled to Earth only two billion years after the Big Bang.

The results of the analysis, showing rapid cooling of the supernova, are published in Nature.

“This is the first detailed look at a supernova at a much earlier epoch of the Universe’s evolution,” says lead author Patrick Kelly. “It’s very exciting because we can learn in detail about an individual star when the Universe was less than a fifth of its current age and begin to understand if the stars that existed many billions of years ago are different from the ones nearby.”

Science’s best estimates suggest the Big Bang, at the beginning of the universe, occurred around 13.7 billion years ago.

It is likely that the first stars formed only 100 million years after the universe was born. But the size, colour and life cycle of these early stars and the first galaxies they began to form remain mysterious.

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Astronomers are hopeful that studying early supernovae and other cosmological events in the early universe will bring greater insight into star and galaxy formation. Ultimately, this will help us better understand our own place in the universe.

The red supergiant analysed in the Nature paper was seen at a redshift of z =3, corresponding to an age of around 11.5 billion years. This means the light from the supernova has travelled 11.5 billion years to reach us. This is about 60 times further away than any other supernova studied to this level of detail.

The star was 500 times larger than our Sun and has yet to be named. It was noticed in images taken of the Abell 370 galaxy cluster in December 2010 by the Hubble Space Telescope.

Using the University of Minnesota’s access to the Large Binocular Telescope, the researchers were able to us follow-up spectroscopy to generate detailed images of the red supergiant. The images were made possible by gravitational lensing, where the mass in a galaxy between us and the red supergiant bends the light from the star, magnifying the light it emits.

“The gravitational lens acts as a natural magnifying glass and multiplies Hubble’s power by a factor of eight,” explains Kelly. “Here, we see three images. Even though they can be seen at the same time, they show the supernova as it was at different ages separated by several days. We see the supernova rapidly cooling, which allows us to basically reconstruct what happened and study how the supernova cooled in its first few days with just one set of images. It enables us to see a rerun of a supernova.”

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This analysis, in conjunction with work done by Kelly on supernovae since 2014, suggest there were more stars exploding in the young universe than previously thought.

“Core-collapse supernovae mark the deaths of massive, short-lived stars,” adds first author Dr Wenlei Chen, also from the University of Minnesota School of Physics and Astronomy. “The number of core-collapse supernovae we detect can be used to understand how many massive stars were formed in galaxies when the universe was much younger.”