The Sun - Nuclear Fusion
The heat and light energy that is produced by the sun originates from the nuclear fusion process that occurs inside the core of the sun. Fusion is the release of energy accompanied by the fusing of two smaller nuclei to make a larger nuclei. The specific type of fusion that takes place in the sun is called proton-proton fusion.
Here are a few facts about the Sun to demonstrate the conditions that result in the nuclear fusion of hydrogen to helium:
- The Sun has a radius 109 times larger than the radius of Earth
- The Sun weighs about 333,000 times as much as Earth
- Over 1.3 million Earths would fit into it the Sun
- The Sun accounts for about 99.8% of the mass of the solar system (Jupiter makes up most of the rest)
- It is the Sun’s temperature and pressure that cause nuclear fusion to begin in the core of the Sun
- The temperature at the core is estimated to be 15.5 million Kelvin
In younger stars, contraction causes a buildup of heat and pressure. Eventually, these two things build to the point of “nuclear ignition”, and this process releases large sums of energy. Once nuclear fusion begins, a balance between gravitational contraction and expansion due to heating from fusion is reached, which eventually halts contraction. The star’s volume is kept fairly constant by this balance of forces, called hydrostatic equilibrium.
The proton-proton fusion cycle begins when two protons, or nuclei of hydrogen atoms, collide to form a nucleus of deuterium. This fusion is followed by the conversion of a small amount of mass into energy. The energy released is enough to cause one of the protons to be converted into a neutron, releasing energy in the form of a positron and a neutrino. The positron kills off an electron, and two gamma rays (γ) are created. The deuterium combines with another proton forming a helium-3 nucleus (3 He) and releases a gamma ray in the process. Then, two 3 He nuclei fuse together to form a normal helium nucleus (4 He), ejecting two protons, which start the process over again.
Spectroscopy determines that the Sun is made up of about 73.5% hydrogen and 24.8% helium (the remainder is made up of oxygen, carbon, neon, nitrogen, magnesium, iron, and silicon). The end result of the proton-proton cycle is that four hydrogen nuclei are fused together to form helium, a small amount of matter is lost, and lots of energy is released.
Works Cited:
Slideplayer.com
Its so interesting how all that energy produced from the sun is all from fusion processes! Why does the fusion cycle have to be between two protons?
ReplyDeleteHi Kathryn, the answer is: alpha particles are the end product of the proton-proton fusion cycle. They are formed by the fusion of two helium-3 nuclei.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteMany people have researched and considered the controversial question of how long the sun will last, and livescience.com claims that the sun will not die for another 7-8 billion years. Without the sun though, life on earth would not exist so the process of nuclear fusion that occurs within its core is incredibly important. How does the sun have enough energy (and where does it get the energy) to repeat the process of nuclear fusion so many times? Also, what is the main difference between the process of nuclear fusion in a young star, and the process of nuclear fusion in older stars?
ReplyDelete