What elements are needed in order for a star to form?

1 Answer
Feb 10, 2016

Hydrogen is the only element required for a star to form.


Hydrogen is the most abundant element. It is also the element which is easiest to start a fusion reaction. When the temperature and pressure at the core of a proto star are sufficient for the protons of the hydrogen nucleus to get close enough for the strong force to be able to overcome the electromagnetic force and start the fusion process.

The hydrogen fusion is called the Proton-Proton or pp chain reaction which is dominant for smaller stars such as our Sun. The process is very inefficient as two protons fuse to create a bi-proton or Helium 2 nucleus. The majority of bi-protons decay back into 2 protons. It requires the much slower weak force to convert a proton into a neutron and form stable Deuterium.

It is thought that the half life of a proton is a billion years before it becomes part of Deuterium. This is fortunate as if the process was faster the Sun would have long ago run out of fuel.

Stars will also contain other elements. Helium 4 is the second most abundant element, but it requires higher energies to become involved in fusion reactions.

Larger stars use Carbon as a catalyst for the CNO (Carbon-Nitrogen-Oxygen) chain reaction. This requires higher temperatures but is more efficient than the pp chain reaction.