Brilliant insight into the dead stars that light up the universe

Scientists have made a major discovery about supernovae – the spectacular light that occurs when stars explode at the end of their lives.

The discovery is a big step forward for astronomers as they use the brightness of supernovae to measure the rate of expansion of the universe. It has been made possible by an international team of astrophysicists including two from Trinity College Dublin and Queen's University Belfast.

Supernovae can briefly outshine entire galaxies and radiate more energy than our sun will in its lifetime. They are the primary source of heavy elements in the universe.

It turns out that “Type Ia supernovae” – which occur following the death of one star that was orbiting another – experience long plateaus of up to a year in their light curves post-death, “rather than fizzling out fast after their final acts”, explained Kate Maguire, assistant professor at Trinity’s school of physics who contributed to the research, published by Nature Astronomy on Monday.

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“These new observations are very exciting as they reveal that many Type Ia supernovae just stop declining as expected and stay bright for up to a year,” she added.

Dr Luke Shingles, of Queen's University Belfast, said the discovery would impact the way astronomers use Type Ia supernova light curves to measure distances and "give us more precise data on the expansion of the universe".

Stars explode

Type Ia supernovae were key to the discovery of accelerating expansion of the universe, which was awarded a Nobel Prize in 2011, but their use in measuring basic cosmological properties "has been limited by how precisely we understand how the stars explode", Prof Maguire explained.

The research was led by Dr Or Graur at Harvard-Smithsonian Centre for Astrophysics in the US.

“Most supernova research is conducted in the weeks or months immediately following an explosion, but we wanted to see how light curves behave at late times, around 500 to 1,000 days after explosion,” he said.

Prof Maguire used one of the European Southern Observatory's flagship telescopes, the Very Large Telescope, in Chile. Her data was combined with observations from the Hubble Space Telescope obtained by Adam Riess of Johns Hopkins University, who won the Nobel Prize in 2011.