How to Make Iron?

At Home In The Universe Essays > Science, IT, Nature

Part 10: And the gold and the silver in the ring around your finger or in your neckless, have also been ‘cooked’ in a supernova explosion.

Supernovae have produced nearly every element occurring in nature, with the exception of hydrogen and helium, both produced by the Big Bang.

When a star is born, it is because it has enough mass to create enough gravity, pressure and heat to sustain nuclear fusion. Fusing hydrogen atoms to helium gives off enormous amounts of energy and the star spends its life quietly fusing away.

Nuclear fusion
Star fusion (Credit: Nicolle Rager Fuller/NSF)

This process takes four hydrogen atoms to fuse into one helium atom. Hydrogen (protium) has only one proton and no neutron, while helium has two protons along with two neutrons. This means that two protons are missing. Matter cannot be created or destroyed, it can only be turned into something else. In this case, the two missing protons have turned into two neutrons. This energy is what makes the star shine and give off heat. Well, after a while of quietly fusing, the star has built up quite a bit of helium.

This helium has found its way to the star’s center to create a helium core. Since hydrogen only has one proton and helium has two protons and two neutrons, it’s heavier. That means the star has a little more mass in its core, which generates more heat. This heat builds up more and more, until it’s hot enough and has enough pressure to start fusing helium to carbon. This process generates a little less energy than fusing hydrogen to helium, but it still produces energy.

As a guideline, a star that has about one half the mass of the Sun is too small and cool to fuse helium to carbon. So it will end up as a white dwarf made of helium. Stars between one half to four times the mass of the Sun are massive and hot enough to fuse carbon to oxygen. Carbon and oxygen are fused more or less at the same time and you’ll end up with a white dwarf made out of carbon and oxygen: a giant diamond in the sky!

Stars with masses greater than four times the mass of the Sun are massive and hot enough to fuse oxygen to silicon.

Stars that have earned the title of supergiant are so massive and so hot, that they begin fusing silicon to a solid core of iron. Once the star starts fusing iron, that’s it– it’s doomed. Fusing silicon to iron takes more energy than it gives off. This means that the star is going to die soon; it is causing its own death by using more of its own energy than it is getting back from nuclear fusion.

Order of nuclear fusion
Order of Nuclear Fusion in Dying Stars

When a star is fusing iron in its core, it’s still giving off insane amounts of energy. The helium, hydrogen, carbon, oxygen and silicon are still there in the star in different shells. Hydrogen is at the surface, still fusing to helium; a little further down, helium fusing to carbon and oxygen; further down we have silicon until the core, where silicon fuses to iron. This is why the star still exists and doesn’t spontaneously explode the moment the first iron atom pops into existence. At this point, the energy process is just no longer exothermic but endothermic. Iron cannot be fused into anything heavier, because of the insane amounts of energy and force required to fuse iron atoms. Stars this massive can turn into several things; it depends on how heavy it is. They can explode into supernovae, collapse into various types of neutron stars or even form a black hole.

Progression Supernova
Image Credit: NASA

To summarize: The rendering above illustrates the progression of a supernova blast. A star spends its life fusing hydrogen into helium. It then starts to fuse elements that are a bit heavier, leading up iron. Once iron comes into the equation, things get very bad very quickly. Suddenly, it’s no longer able to sustain equilibrium, so its core collapses in on itself and it casts off its gaseous envelope in one fell swoop, sparking a supernova. Later on, the remainder of its gas gets energized by the core it leaves behind, either a pulsar or a neutron star (sometimes, if the star is massive enough, it leaves a stellar-mass black hole behind instead), and it glows brilliantly for a time. We call these amazing things supernova remnants.

Crab Nebula
The Crab Nebula – Image Credit: NASA, ESA, J. Hester, A. Loll (ASU)

The Crab Nebula, the result of a supernova noted by Earth-bound chroniclers in 1054 BCE, is filled with mysterious filaments that are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The Crab Nebula spans about 10 light-years. In the nebula’s very center lies a pulsar: a neutron star as massive as the Sun, but with only the size of a small town.

The Crab Pulsar rotates about 30 times each second.

All credit goes to Jordan Lejuwaan  and to NASA

ShantiShanti is a regular contributor to Osho News

All articles of this series can be found in: At Home in the Universe

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