Stellar Evolution - Stellar Evolution 1. Process a. Begins...

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Stellar Evolution1.Processa.Begins with stellar cloud with protostarsb.(Majority): Small star---red giant---planetary nebula---white dwarfc.Large star---red supergiant---supernova---neutron star or black hole2.Energy Liberation in Stars and Stellar lifetimea.Stars know how to transform light elements into life-giving heavyelementsb.The process is vital in determining the temperature around the starover the course of millions of yearsc.The Sun has shone steadily for nearly 5 billion years and will shine foranother 5 billion yearsd.The two important factors for emergence of life from the POV of thestars seems to be their lifetime and luminosityi.Stellar lifetime limits the duration of time for emergence andevolution of life as we know it on a planet orbiting a starii.High mass stars have very short life times and hence may nothave enough time for intelligent life or complex life to developiii.Our sun seems a perfect example, humans are intelligent lifeand have evolved in the middle ages of our sune.Stellar surface temp and apparent brightness can be relativelyprecisely determinedi.Stellar temp is measured using optical spectrograph (Kelvin)1.Stars with different mass have different continuumspectra and different “fingerprints” that determinedifferent spectral type2.Order of spectral mass and temp (decreasing)a.“Oh, Be A Fine Guy, Kiss Me”b.Our Sun is a G typeii.Apparent brightness is measured using an astronomicalcameraiii.Temperature-Luminosity Diagram (Hertzburg-Russell, HR)1.90% of stars are on the Main Sequence2.Stars with higher surface temp have much greaterluminositiesiv.The Hydrogen burning activity makes the star spend of theirlifetime on the Main sequence1.Proton-proton cycle: 4 protons---helium-4 + 2neutrinos+ energy2.70% of the matter in stars is hydrogen, which keeps thestar alive for a whilea.Reaches main sequence when the core reaches100 million K and the hydrogen can burn, 3helium fuse together to form carbon and then thestar stabilizes
3.Summarya.The total lifetime of a star depends on its massb.Stars with higher mass burn themselves out far more rapidly thanstars with lower masses doc.Inside the sun, the proton-proton cycle releases a grand total of 41033ergs of energy per second, 10,000 times more energy than the humanrace has consumed during the past 5000 years!d.When the central temperature of a protostar reaches 10 milliondegree K, the proton-proton cycle of nuclear reaction beginsgenerating kinetic energy from mass energy. This released kineticenergy halts the contraction of star due to its self-gravity.e.The balance between gravity and pressure (kinetic energy) leadsnaturally to a constant rate of energy production and to a constantluminosity for the starf.Higher mass star has higher gravity in the central, requiring higherpressure (temperature) to balanceg.Higher temperature inside the star leads to faster nuclear fusion,therefore, a high mass star burns itself faster than a low mass stari.

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Term
Spring
Professor
Eikenberry
Tags
Solar System, Black hole, White dwarf, high mass stars

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