Elements after iron forming?

Question

When a star begins to die and collapse into itself it attains very high temperature and pressure within its core and is then able to fuse atoms into iron. From this point all fusion of iron takes energy from the star as no other element with a higher atomic number has a nucleus as tightly bound as iron's.

So does the Fusion process still continue for awhile producing other elements from iron or is there some other process I should know about?

Any information about the natural formation of elements would be nice.

Answer 1

Heavy elements are made inside stars - but they do NOT have to be massive stars that supernova.

Neutron capture is the key to building elements heavier than iron.

Neutrons are neutral and so there is no electrostatic repulsion when trying to add neutrons.

In a star that goes supernova many neutrons are freed and can be injected into nuclei. This process happens so fast that nuclei become full of neutrons and unstable, so they decay radioactively. The path by which they decay depends on what the element started as and how many neutrons were added - but this process, known and the r-process (rapid process) leads to a certain distribution of isotopes.

However, it is a myth that lower mass stars, like the sun, cannot build elements heavier than carbon. Inside an aging low mass star neutrons get produced and neutron capture can occur. In this case, the neutron density is much lower, to the process is much slower (s-process). This leads to a different set of isotopes than the r-process!

These low mass stars lose their newly made elements much more slowly than massive stars and the ejected material is what eventually forms planetary nebulae.

See: http://en.wikipedia.org/wiki/S-process

and: http://en.wikipedia.org/wiki/R-process

In fact fusion beyond iron can occur but it is very inefficient and leads to a core collapsing even faster and energy is consumed in the fusion process. So although a few atoms veavier than iron can be made by fusion, neutron capture is the most improtant process.

Answer 2

The process is called nuclear spallation, and it's unrelated to fusion although it's still a nuclear process.  It occurs in supernova explosions, but also in cosmic rays and particle accellerators.  The violent collapse of a stellar core produces so much heat and radiation that atoms in the rest of the star begin to recombine randomly.  This produces a lot of heavy elements, including short-lived radioactive ones which contribute to the supernova's afterglow.  I've also heard that merging neutron star binaries produce far more heavy elements per event, although they're much more rare.

Answer 3

No...iron just is simply to heavy to fuse. It is the last step in the process, when there is no more of the elements leading to iron, the star's outer and inner atmosphere collapses inwards, the ability to keep it sustained having gone (for example removing the foundations of a building). Once the shock wave hits the solid core, the "fusion" into heavier elements is created, as the iron undergoes enormous compression and other forces. This creates some of our heaviest elements. The compression wave then bounces back outwards in the spectacular explosion we call supernova.

Answer 4

Stars can't generate sustainable energy by producing elements heavier than iron but that doesn't mean that the reactions don't happen, it's just that they consume energy.  As long as the internal conditions in the star are right some of these processes will take place.

Try looking up the "s-process".  (The "r-process" is what happens during a core-collapse supernova and is another way of generating elements heavier than iron.)

Answer 5

Do you mean how do elements past iron form?

If so, then here:

Elements heavier than iron on the periodic table form in massive supernovae explosions, this is why the further down the periodic table you go, the less there is of that element (although earth is slightly different).

Also, the Fusion process requires more and more energy the heavier the atoms are. The larger the star, the more energy is available. This means only certain elements before iron can be created by smaller stars, such as our own.