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Name: Wilfred
Status: educator
Grade: 6-8
Country: USA
Date: Winter 2012-2013

When a star fuses hydrogen into helium it starts to create iron in the core . If a star is large enough does the star explode immediately, when it begins to create iron or when there is no more helium to fuse into iron? Iron is the catalyst of the death of a star.

Dear Wilfred,

Hydrogen and helium do not immediately fuse to iron. They fuse to successively heavier elements, of which iron is the last. That process can last millions of years in a big star. But when iron is finally formed, it will not fuse further and stellar fusion stops cold. The star implodes, then the outer layers explode as a supernova.

Great question! Sincerely, David Levy

Hi Wilfred,

Thanks for the good question. A star will fuse hydrogen into helium. Helium then undergoes fusion to form other elements. Eventually, after many fusion events, iron will result since it is the most stable. The star does not explode immediately upon fusing, but later in the life cycle. Let me pose a question for you: If iron was the catalyst for the destruction of a star, then how can how can elements beyond iron (such as lead) be formed?

I hope this helps. Please let me know if you have any further questions. Thanks Jeff Grell

Iron is not created immediately. Iron is the last product of a sequence of fusion reactions. When core hydrogen is depleted, the core contracts until helium fusion begins, and so on. Once the core cannot release energy by fusion (when it is iron) it collapses to initiate the supernova.

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy University of Wyoming

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