Astronomers have new information on how stars age and die – and it's not what they thought.
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The findings from an Australian-led study overturn conventional thinking that the "red giant phase" is the last stage in a star's life.
Led by Monash University stellar astrophysicist Simon Campbell, the results mean the standard computer models that astronomers use to measure the lifespan of stars, including the sun, will have to be adjusted.
"We've found something that is substantially wrong with the model used on stars that are a similar mass to the sun," Dr Campbell said. "And these models are quite fundamental to astrophysics."
Using the European Southern Observatory's Very Large Telescope in Chile, the researchers studied a large cluster of stars in the Milky Way, 13,000 light years from Earth.
Of the one million stars in the globular cluster known as NGC 6752, about 70 per cent failed to reach old age – which, if you're a star, is the most productive stage of life.
"That's when they blow off all their outer layers," Dr Campbell said. "It really is the last death throes of their life."
The dust and gasses that are expelled from dying stars are recycled and over billions of years and can form new stars and even planets.
The red giant phase is named after the colour of the star's surface, which glows red hot towards the end of its life. Stars in the red giant phase are the brightest stars in clusters – and the results mean that there will be 70 per cent fewer bright stars than current models predict.
It was thought that stars go through the red giant phase twice: once in early life before they enter the blue giant phase and then again at the end of their lives.
"But what's happening is that 70 per cent of the stars in this cluster just aren't getting to that last red giant phase," Dr Campbell said. "Somehow they have died young."
Published in the journal Nature on Thursday, the study also found that the stars which died before reaching old age also had high sodium levels. However Dr Campbell believes this was not the cause of a star's death but a "chemical tag" indicating which stars would die prematurely.
Globular clusters are some of the most ancient objects in the universe. Understanding how stars evolve is key to learning about the formation of the universe. They are as old as the universe itself – dating back about 13 billion years.
"Everything around us is formed from stardust... they are one of the main building blocks of our universe," he said.
Discovered in 1826, the cluster studied is in the constellation of Pavo. It is one of 158 in the Milky Way and the research team plan to study others to confirm that the pattern holds. But Dr Campbell said he expected the results would be repeated.
