![]() This cycle is shown in the diagram above to the right. As you can see, C-12 is not used up in this reaction, but it acts as a catalyst that is essential for the reaction to occur (Australia Telescope Outreach & Education, 2004 ). This C-12 nucleus is then able to start another cycle of the same sequence of reactions (as C-12 is what began this initial sequence). When N-15 fuses with a proton, the resultant nucleus splits to form a He-4 nucleus and a C-12 nucleus. This C-13 fuses with another proton, creating N-14, which fuses with another proton, creating O-15. This O-15 is also unstable, so it decays into N-15. This N-13 nucleus is unstable, eventually decaying into C-13. In this reaction, a proton fuses with a C-12 nuclei, producing an N-13 nucleus. The CNO stands for carbon, nitrogen, and oxygen, and the reaction is cyclical (as the name suggests). The net equation for this reaction is: As such, main sequence stars that undergo this equation have warmer temperatures. This process is used by more massive stars, or those that have 1.5 solar masses or more. The following link will direct you to a Proton-Proton Hydrogen Fusion Simulator that plots several variables that result in the binary fusion processes: Ī second process that is used to provide the necessary energy for nuclear fusion in main sequence stars is the CNO cycle. The diagram below on the left shows the PP Chain in action ( ). After this though, the reactions take very little time to occur. On average, a hydrogen nucleus waits 1 billion years before it interacts with another hydrogen nucleus to begin the sequence. The rate at which this reaction occurs depends on the time it takes for the reaction to first occur. The reaction also produced 2 neutrinos, 2 photons, and 2 positrons (Australia Telescope Outreach & Education, 2004). In this reaction, 4 hydrogen nuclei protons are fused in the star's core, producing a helium-4 nucleus. The PP Chain, as it is commonly called, accounts for about 85% of the energy released in the sun (Australia Telescope Outreach & Education, 2004). This process takes place in stars with cooler temperatures, which is why they have lower masses. The main process responsible for providing the energy source in main sequence stars is the proton-proton chain, which is the process used by our sun and other stars with less than 1.5 solar masses. This is due to hydrogen continually being fused into helium as the sun has gone through nuclear fusion. For instance, fusion has been ongoing in the core of the Sun for about 5 billion years, and its core is now about 29% hydrogen, 70% helium and 1% everything else. The chemical composition of stars changes as nuclear fusion occurs. Refer to the diagram to the right for a visual representation of nuclear fusion. As a result, the star is said to be in equilibrium and the nuclear fusion prevents the star from being further collapsed. When this happens, pressure from within the core exerts force outward, which acts as a balance with the force of gravity pushing inward. Eventually, the core will become hot enough for hydrogen to be burned into helium. As gravity pushes the star inward, the core of the star will contract and heat up. This occurs because gravity is constantly exerting its force inward towards the core of the star. By doing this, the main sequence star is essentially remaining in a state of hydrostatic equilibrium. ![]() ![]() In order for nuclear fusion to occur, the core of the star must reach a temperature of approximately 10 million Kelvin. In main sequence stars the hydrogen is burned in a star's core and converted into helium. Nuclear fusion is the process by which "light nuclei combin to form heavier nuclei," which produces energy from combination of elements lighter than iron ( ). To fully understand a main sequence star, it is important to understand the process of nuclear fusion. ![]() This composition shifts as hydrogen is fused into Helium via nuclear fusion. The general composition, by mass, of main sequence stars is 74% hydrogen, 25% helium, and 1% other heavier elements. For instance, a star such as our sun will undergo nuclear fusion for approximately 10 billion years ( ). The vast majority of a star's existence is spent as a main sequence star the estimation is 90% of stars in the universe are main sequence stars. Main sequence stars all share similar properties in terms of the relationship between their masses and their luminousities, temperatures, and lifetimes. A main sequence star is a star that is currently going through nuclear fusion, which in short, is the process of fusing hydrogen into helium in the star's core. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |