Eureka: The Death of Stars

By Stephen Cass | September 18, 2008 3:46 pm

Screen capture from Euraka Season Three, Episode SevenOn Tuesday’s nights Eureka, a miniature sun was accidently born in the skies above the town, wreaking destruction. The solution? To shoot iron into the sunlet’s core.

This is in fact not far off how some real stars die: iron poisoning. Stars exist via a balancing act between two forces. The first force is the star’s own gravity, which produces an inward compression. At the core of a star this compressive force creates the conditions that allow fusion reactions to occur. Left unchecked, gravity would cause a star to collapse in on itself. Gravity is balanced by the second force, an outward pressure that comes from the core of the star, where the nuclear fusion reactions release huge amounts of energy. This outward pressure is constantly trying to blow a star apart, but is restrained by gravity.

Normal, healthy, stars fuel the reactions in their cores by burning hydrogen. When hydrogen atoms are burned in a fusion reaction, they are smashed together to form helium, releasing energy. However, eventually the time comes when the star uses up so much of its hydrogen that it can no longer sustain hydrogen fusion. In real stars what happens next is complex, but in essence, the outward pressure falls, so gravity squeezes the core tighter, raising its temperature. This gives the star a new lease on life because the core is now so hot that it can repeat its energy-from-fusion trick, balancing gravity again. But this time the core is fusing helium atoms into even heavier carbon atoms. Unfortunately for the star, turning helium into carbon doesn’t release as much energy per atom as fusing hydrogen into helium. Eventually too, the helium will run out–and the star will collapse further. If the star was massive enough to begin with, the star can continue to produce energy by fusing the carbon, and the cycle repeats, with heavier and heavier elements being fused together–with less and less energy being produced each time.

Eventually an element is formed that will release no energy if used as the raw material for a nuclear reaction (in fact, it would cost energy to fuse.) This element is–surprise, surprise–iron, and it pretty much marks the end of road for a star. The star can no longer fuse atoms as fuel for its reactions. Pressure can no longer balance gravity. Gravity finally and utterly wins control of the star’s fate. The resulting implosion of the core creates a shockwave that blows away the outer layers of the star, producing a supernova. Thus the star dies in one of the most violent and spectacular explosions known to astronomy.

CATEGORIZED UNDER: Astronomy, Physics, Space, TV

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