South Oakleigh College ASTROPHYSICS: Proton Proton Chain Reaction

Tuesday, October 25, 2011

Proton Proton Chain Reaction

The proton–proton chain reaction is one of several nuclear fusion reactions by which stars convert hydrogen to helium. The Sun which consits mainly of Hydrogen (75%) and Helium (24%) is emiting its light energy due to fusion of protons into helium.

Proton–proton fusion can occur only if the temperature (i.e. kinetic energy) of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion.

In the Sun, deuterium-producing events are rare. The fact that the Sun is still shining is due to the slow nature of this reaction; if it went more quickly, the Sun would have exhausted its hydrogen long ago.

The first step involves the fusion of two hydrogen nuclei 1H (protons) into deuterium, releasing a positron and a neutrino as one proton changes into a neutron.

1
1H

→

2
1D

ν
e

0.42 MeV

This first step is extremely slow, both because the protons have to tunnel through the Coulomb barrier and because it depends on weak interactions.
The positron immediately annihilates with an electron, and their mass energy, as well as their kinetic energy, is carried off by two gamma ray photons.

e−

→

2 γ

1.02 MeV

After this, the deuterium produced in the first stage can fuse with another hydrogen to produce a light isotope of helium, 3He:

2
1D

1
1H

→

3
2He

5.49 MeV

From here there are three possible paths to generate helium isotope 4He.

The complete proton-proton chain reaction releases a net energy of 26.7 MeV.

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AstroPhysics

Astronomy or Astrophysics is the scientific study of stars, planets, comets and galaxies. Astronomy is one of the oldest sciences when people sought to understand the bright lights in the night sky. The invention of the telescope enabled great progress to be made.

The scientific age began when Galileo Galilei , in Florence, Italy built a telescope similar to the design created by Hans Lippershey In 1610 Galileo published his findings that Jupiter had moons. As a result of Galileo's observations he theorised that the Sun is orbited by Earth and the planets. That the moon is not a planet but orbits the Earth. That Jupiter has its own moons. He challenged the belief that the Earth is the center of the Universe with all the planets, the Sun and the Moon and the Stars in orbit around around the Earth.
Galileo also used his telescope to discover that the Milky Way is composed of stars.

Modern telescopes on Earth have discovered a lot of other galaxies other than the Milky Way, during the 20th Century. It was Edwin Hubble who discovered in 1923, that galaxies exist outside of the Milky Way.

In 1990 a telescope, known as the Hubble Space Telescope, was launched into orbit around the Earth, 600km above the Earth and therefore above the Earth's atmosphere. Being above the atmosphere means that the images captured by the telescope are much clearer than are possible on the surface of the Earth, and therefore much more distant objects can be seen and analysed. Check out these sites [ http://hubblesite.org/ and http://hubble.nasa.gov/ ]