Where Does Energy Come From?

Synopsis

1. The total amount of energy (in all forms) in the Universe is constant.
2. Local concentrations of energy were created
   • through star formation, and
   • in heavy elements formed during supernova explosions.
3. All energy available on Earth comes from
   • our local star (the Sun), or
   • from energy within the nuclei of heavy elements.
4. For anything to happen, energy must be transferred.

Sources of Energy

Luckily, the Laws of Physics are cast in such a way that tiny fluctuations in the energy distribution of the early Universe has lead to huge gradients in the energy distribution of the Universe as we observe it today, filling space with clusters of intensely hot blobs of gas known as stars.

The first stars to form were primarily made of hydrogen (and some helium). The core of these first stars fused hydrogen into helium and other elements eventually forming cores of iron and releasing huge amounts of nuclear energy in the process. A very few of these stars were so large that as they ran out of nuclear fuel they exploded in a supernova. Supernova explosions are so powerful that they produce trans-uranium elements as well as highly radio-active isotopes of other elements of all types.

Supernova explosions enrich the interstellar medium with heavy elements.

These elements are mixed into the material that will eventually form second and later generations of stars..of which our Sun is an example. The Sun contains "enriched" inter-stellar material, contaminated by traces of heavy elements synthesized in an ancient supernova explosion which occured billions of years before our Sun and its system of planets formed.

Transparency Master Remnant of a supernova, known as the Crab Nebula . National Optical Astronomy Observatory, Kitt Peak, Arizona.

The image to the left is the remnant of a supernova explosion. This is popularly known as the Crab Nebula and it harbours a rapidly spinning neutron star at its center. The energy from the explosion synthesizes radio-active isotopes and tran-uranium elements which are ejected at high velocity into the surrounding interstellar medium. AMAZING FACT: Almost every atom in your body (except hydrogen) was created by nuclear processes inside a star or in a supernova explosion.

Transparency Master Image of the Sun's surface National Solar Observatory, Kitt Peak, Arizona

The Sun is basically a huge ball of hydrogen gas held together by the gravity created by its own mass. Under the intense pressure created at the centre of the Sun by gravity, hydrogen nuclei are fused together to produce helium nuclei. Very simply stated, four hydrogen nuclei are fused into one helium nucleus, however one helium atom has less mass than four hydrogen atoms. The fusion process releases enough energy to account for the lost mass. The energy released by nuclear fusion in the Sun's core heats the Sun. The hot Sun radiates light into space, warming the Earth and the other planets. About 1300 watts per square metre reaches the Earth's orbit, of which about 1000 watts per square metre reaches the Earth's surface (on a clear day).

Summary

1. Energy from nuclear fusion within the Sun,
2. Energy from the nuclear fission of heavy elements (such as uranium), either natural radioactivity, or from nuclear reactors.