ASTR 1102 Chapter : Astronomy 1102
Document Summary
Nuclear reactions: burns hydrogen to helium, stronger at high temps, rate varies as t^4, 10% hotter means 50% faster. Helium burning: triple-alpha rxn: takes over when core hydrogen is exhausted, needs higher temp 100mil k. Our sun was only 70% as bright as it is now. The sun is gradually converting hydrogen into helium. For the same temp and density helium has lower pressure than hydrogen. Carbon dioxide rich atmosphere => greenhouse warming (greenhouse gases) Even now, small co2 content of air keeps earth ~25 degrees warmer than it otherwise would be. Ms lifetime is time to burn all hydrogen in the core. Assume core mass (nuclear fuel) varies with total mass. G star, 1. 0m lasts 10 billion years (sun) O star, 25m 100,000l lasts just 2. 5 million years. Total mass over mass per second being destroyed gives you the amount of time. Energy from fusion comes from amount of mass being destroyed. Being on the main sequence burning hydrogen.
