Birth of a Star
Stars are formed from interstellar clouds - a massive cloud of gas and dust floating about in space. Gravity pulls this cloud closer and closer together, getting denser and denser, until...
...a protostar is formed. The temperature of a protostar is not yet hot enough to undergo nuclear fusion, but will still glow faintly just from the excitation of electrons - the same way that a heated metal bar will glow as well. Eventually, as it continues collapsing under the influence of gravity, the temperature reaches a critical threshold and the star becomes hot enough to support nuclear fusion. A chain reaction of helium being formed from isotopes of hydrogen kicks in, rapidly propagating through the core, and birthing...
Main Sequence Stars
a star at last! This star is known as a main sequence star - which simply means a star that fuses hydrogen into helium in its core. This happens through a process called the proton-proton chain, in which helium-4, the most abundant isotope of helium, is produced. This happens through the following 3 steps, generating excess heat and light at each step (as per
protons (hydrogen nuclei) fuse to produce a deuteron (deuterium nucleus), plus a positron and electron neutrino.
deuteron from step 1 fuses with another proton to form helium-3 and release a gamma ray.
- At this point there are four possible branches, however the main branch involves two
helium-3 nuclei fusing, producing helium-4 and two protons (which can be reused in step 1).
This can be summarised by the following three nuclear equations:
And thus, the overall reaction can be condensed into the following monster equation:
Despite us only having
Stars emit much more electromagnetic radiation than protostars actively from the nuclear fusion reaction, which also prevents the star from collapsing in on itself thanks to a delicate balance of gravitational equilibrium. The vast amounts of energy released creates a force pushing outwards from the centre, opposing the gravitational force pulling the star inwards.