What Happens When an Enormous Star Blows Up?
What happens when a really gargantuan star - one hundreds of times bigger than our sun - blows up?
Although a theory developed years ago describes what the explosion of such an enormous star should look like, no one had actually observed one - until now.
An international team, led by scientists in Israel, and including researchers from Germany, the US, UK and China, tracked a supernova - an exploding star - for over a year and a half, and found that it neatly fits the predictions for the explosion of a star of over 150 times the sun's mass.
Their findings, which could influence our understanding of everything from natural limits on star size to the evolution of the universe, appeared recently in Nature.
'It's all about balance,' says team leader Dr. Avishay Gal-Yam of the Particle Physics and Astrophysics Department. 'During a star's lifetime, there's a balance between the gravity that pulls its material inward and the heat produced in the nuclear reaction at its core, pushing it out.
In a supernova we're familiar with, of a star 10 -100 times the size of the sun, the nuclear reaction begins with the fusion of hydrogen into helium, as in our sun. But the fusion keeps going, producing heavier and heavier elements, until the core turns to iron. Since iron doesn't fuse easily, the reaction burns out, and the balance is lost. Gravity takes over and the star collapses inward, throwing off its outer layers in the ensuing shockwaves.'
The balance in a super-giant star is different. Here, the photons (light particles) are so hot and energetic, they interact to produce pairs of particles: electrons and their opposites, positrons. In the process, particles with mass are created from the mass-less photons, and this consumes the star's energy.
Again, things are thrown out of balance, but this time, when the star collapses, it falls in on a core of volatile oxygen, rather than iron. The hot, compressed oxygen explodes in a runaway thermonuclear reaction that obliterates the star's core, leaving behind little but glowing stardust. 'Models of 'pair supernovae' had been calculated decades ago,' says Gal-Yam, 'but no one was sure these huge explosions really occur in nature. The new supernova we discovered fits these models very well.'
"Kepler's supernova remnant. The explosion of a star is a catastrophic event. The blast rips the star apart and unleashes a roughly spherical shock wave that expands outward at more than 35 million kilometers per hour (22 million mph) like an interstellar tsunami. What might happen when a really gargantuan star - one hundreds of times bigger than our sun - blows up? (Credit: NASA)"
Source: Weizmann Institute of Science
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