Tag Archives: star formation

The lifecycle of iron (part 1)

Out in the deep, darkness of interstellar spaces, the coldness is absolute. Dust and gas gathers slowly, too cold to move any quicker, leftover remnants from a violent explosion is the long forgotten past. The dust creates an interstellar cloud, the dark nebula, so laden with beauty if there were but any light to see it. Time and gravity are in control here, and if the cloud cools just…enough…the density within the core of the cloud reaches a tipping point, pushing the dust and gas into collapse. As the molecules are pushed closer and closer together by the unrelenting force of gravity, the density and the heat rises and a protostar is formed.

The vast dust clouds are at first dark. As the protostars grow, they feed of the matter around them and become hotter and more stable. In a wink of a galactic eye, barely some few million years, thermonuclear fusion begins in the core and accretion of new material stops. Hydrogen, the most abundant element scattered through the stellar nursery, forms the body of the young star, and once burning begins, light is scattered by strong stellar winds out into the wider universe. As time passes,  we find the cluster of young stars (once deep within the core of the gas cloud) scatter the remaining gases leaving only themselves. Time passes slowly and for countless millions of years the stars burn brightly – vast amounts of energy released as the hydrogen nuclei are fused into helium.

However, mass is finite, and the supply of hydrogen eventually runs out as the star approaches the end of its life. Fusion continues, first with helium nuclei fusing together to make carbon, and carbon and helium create oxygen. If there is enough fuel, fusion will continue as the star grasps to extend its lifetime, moving though neon, magnesium and silicon in a matter of weeks. Eventually as the final bell tolls, the silicon nuclei in the core fuse into iron – the most stable element known to us – and cannot be fused further without putting more energy in (thereby dropping the temperature), so finally depleting the fuel in the core, in under a day.

In the massive stars where this happens, the sudden cessation of energy release causes the core to collapse suddenly and violently, the outer layers imploding onto the inert iron core with so much force they explode as a supernova, burning brighter than the entire galaxy for the briefest of moments, before silencing. As the remnants of the core collapse at last into a neutron star or further into a point of infinite density, the rest of the matter is ejected back out into space.

Slowly but surely this matter starts to clump together in the dark and so the cycle begins again.