PS 1063 Week 11 Chapter 10 Stellar Lifetimes Stars go through phases that share analogies with the life cycles of many organisms. Star Formation→ Gestation/Birth Main Sequence→ Prime of Life Post-Main Sequence→ Old Age End of Energy Generation→ Death Mass dictates everything for a star existence: demise, etc. Star formation process begins in the interstellar medium (ISM) Conditions are best in Cold Molecular Clouds. Solar Nebula Theory Cloud of gas and dust falls in an itself and rotates. Rotation mass is flattened into a disk. Forming a Star Inside a nebula, material starts to collapse. Material flattens out into a disk around the forming star, called a protostar. Young Stellar Objects Disk of accreting material, black our view of Protostar. As it matures, more of it is it gets bigger and hotter as the disk thins out. Lower Mass stars (G, K, M) use the Proton-Proton- Chain Higher Mass Stars (O, B, A, F) use the CNO Cycle Chapter 11 How long do you think a star remains in its Main Sequence phase 90% Contracting core continues to get hotter and denser. Layer of hydrogen outside care begins fusion. If massive enough, nuclear reactions involving helium begin in core. Triple= Alpha Process Alpha Particle= Helium Nucleus