A star 'hiccupping' before it dies observed for the first time

A giant "hiccupping" star in the last stages of its life before exploding has been documented for the first time by researchers.

The international team - including from Queen's University Belfast - were able to record the event by coordinating observations from telescopes around the world.

Previously a theoretical concept but never observed, Pulsational Pair Instability (PPI), or "hiccupping" happens when a star develops a very hot core, which contracts and expands quickly in the final phase of its life.

Every time the star pulsates, it ejects shell material which strips down the core star. These shells can then collide with each other, creating intense bursts of light.

It can only take place with exceptionally large stars between 60 to 150 times the mass of our sun.

Lead author Dr Charlotte Angus, from the Astrophysical Research Centre (ARC) at Queen's University, said that because the shell collisions are much fainter than the final supernova - a massive explosion when a star dies -, it had previously not been possible to confirm the theory.

"In December 2020, we identified a new bright supernova, now named 'SN2020acct', in a nearby spiral galaxy called NGC 2981," she said.

"The light from SN2020acct disappeared pretty quickly. But then in February 2021, we saw light coming from the same region of the galaxy again.

"This is very unusual as supernovae normally don't reappear."

Researchers tracked the supernova using telescopes in Hawaii, Chile, South Africa and the US, and found that when it appeared for a second time, it was expanding much faster.

It suggested that the core of the star had exploded, marking the end of its life. The astrophysicists then used modelling to confirm that the first flare was an example of PPI.

Scientists said the star was around 150 times the mass of the sun, and underwent a series of extreme pulses in the final 50 days before it exploded.

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"This is the first time that we have ever obtained observations of a PPI candidate during the shell collisions, allowing us to confirm for the first time that this is really happening," Dr Angus added.

"That the data matches the modelling predictions is incredibly exciting."

The results of the study were published in Astrophysical Journal.