Nuclear Processes
The Fusion Process
As you already know, stars produce energy by nuclear fusion. But, what is nuclear fusion? Fusion occurs in the core of a star, and it is the process of combining lighter elements into heavier elements. Since the most common element in the Sun (and other stars) is hydrogen, it is this element that is fused together to form the element of helium. When fusion occurs, four hydrogen nuclei are fused together to make one helium nucleus. Helium has less of a mass than the four hydrogen nuclei combined. This leftover mass is converted into energy. During the individual process, it is a very small amount of mass that that is converted into energy, so many reactions must occur simultaneously and continuously in the core of stars. Astronomers know that for a larger amount of reactions to take place, the area must be very dense with very high temperatures.
Nucleosynthesis
As the nuclear reactions produced by fusion take place in the star, new elements are created. A star's mass will determine what type of elements will be synthesized, or created. Smaller mass stars will continue the fusion process, and hydrogen will convert into helium. Medium-sized stars, like the Sun, will eventually convert helium into oxygen and carbon. Massive stars will also convert helium into oxygen and carbon. These massive stars will also create many more elements from later reactions.
Learn more about how stars create elements by viewing the video The Elements: Forged in Stars from eMediaVA℠. As you view the video, consider the following questions:
- What elements make up young stars?
- Why do you think it takes a tremendous amount of heat and pressure to create helium (and then carbon, etc.)?
The Depletion of Hydrogen
During the process of fusion, helium is made, along with energy. Due to the extreme heat and pressure in a star’s core, these atoms move much faster. The faster they are moving, the harder they will collide. They will combine and more reactions will occur. Stars will deplete the hydrogen needed to create helium in the fusion process as the star moves through its life cycle.
Stars go through different stages in their life cycles based the amount of gas with which they start. The life cycle of a star depends on how well a star can control the process of fusion. The Sun is an average star in every way. It is roughly half-way through its life cycle. Scientists theorize that the Sun will begin to run out of hydrogen in its core in around 5.4 billion years and become what is known as a red giant. The Sun will become larger and cooler as time progresses. Then, the Sun may possibly become a dwarf star as it runs out of hydrogen.
Nuclear Fission
Fission is the process of breaking down a larger atom into a smaller atom. In the process of dividing the nucleus of larger atoms, an immense amount of energy and light is released. This is the process that nuclear power plants use to split a large atom to make energy. Usually, the fission process takes place when a uranium nucleus that contains 235 protons and neutrons is split. Once the nucleus is split, the fragments are more tightly bound and energy is released as a by-product. This is not a process that takes place in stars; however, it is a process that is used to generate energy on Earth.
Nuclear Processes Review
Check your knowledge of nuclear processes in this non-graded activity. Read each question and select the appropriate answer. Then, click SUBMIT to check your response. Click the player to get started.