How do stars die?

Focus-Science and Technology - - Q&A - LES­LIE GRIF­FIN, MALVERN AGu

Stars die be­cause they ex­haust their nu­clear fuel. The events at the end of a star’s life de­pend on its mass. Re­ally mas­sive stars use up their hy­dro­gen fuel quickly, but are hot enough to fuse heav­ier el­e­ments such as he­lium and car­bon. Once there is no fuel left, the star col­lapses and the outer lay­ers ex­plode as a ‘su­per­nova’. What’s left over af­ter a su­per­nova ex­plo­sion is a ‘neu­tron star’ – the col­lapsed core of the star – or, if there’s suf­fi­cient mass, a black hole.

Av­er­age-sized stars (up to about 1.4 times the mass of the Sun) will die less dra­mat­i­cally. As their hy­dro­gen is used up, they swell to be­come red giants, fus­ing he­lium in their cores, be­fore shed­ding their outer lay­ers, of­ten form­ing a ‘plan­e­tary ne­bula’. The star’s core re­mains as a ‘white dwarf’, which cools off over bil­lions of years.

The tini­est stars, known as ‘red dwarfs’, burn their nu­clear fuel so slowly that they might live to be 100 bil­lion years old – much older than the cur­rent age of the Uni­verse.

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