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Download Recap: High Mass Stars
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Life Cycle of Stars • 1st Step: –Stars form from nebulas • Regions of concentrated dust and gas left from the BIG BANG (or other stars’ demise) –Gas and dust begin to collide, contract and heat up • All due to gravity, even the smallest particle has gravitational attraction! –[What 2 things affect gravity?] Eagle Nebula Orion Nebula Horsehead Nebula Triangulum Nebula • 2nd Step: – As nebula contracts, a small star is formed • Called a protostar – Eventually, the protostar will begin nuclear FUSION • Hydrogen protons attract to each other – Strong nuclear force (Nucleus particles stick) » Heat (15,000,000° C) + gravity and….. \FUSION begins • Continued FUSION is necessary for stars to survive. • Can take 30,000,000 years for protostar to form • 3rd Step: The HertzsprungRussell Diagram – Star joins the main sequence • 90% of stars spend life here • Nuclear fusion = Hydrogen into Helium • Mass of star determines location on main sequence • Ranges in size from ½ Sun to 20 times the Sun’s size • Color depends on the surface temperature • Beginning of the End: – Stars begin to die when they run out of hydrogen • Gravity begins to take over Really Low Mass Star • Doesn’t burn Hydrogen (dud) • Begins to cool and forms a Brown Dwarf Low Mass Stars • From ½ all the way down to 0.075% of the Sun’s mass • Burn cool, less than 3500 K. Dim light. • Can live a REALLY long time. 10,000,000,000,000 years? • Our nearest star neighbor is Proxima Centauri, a red dwarf. • Most numerous stars in the entire Universe! Intermediate mass Stars (like the Sun up to 5x Sun) – Star core begins to shrink; outer core of hydrogen begins to fuse and expand • Star gets bigger Red Giant! Eventually the outer shell is blown off (planetary nebula) and the remaining core is a white, hot and small… White Dwarf! High Mass Stars—form supergiants! Supergiant Red Giant S S • Core is no longer fusing (iron is it!) • The balance of pressure loses and the entire star collapses • Massive explosion – Creates heavier elements Supernova! Neutron Star • Star with a core from 1.4 to 3 times the size of the Sun becomes a neutron. • Electrons and neutrons combine into neutrons. • 10 km (6 mi) in diameter with a mass more than our Sun! • A teaspoon of neutron star would be about 10 million tons • Acts like a huge magnet with magnetic poles, can be a pulsar What is a Black Hole??? – An object so massive and dense that not even lightBlack can escape its gravity Holes Info Sheet – The end result from a supernova that leaves a core of 3+ times the Sun. – Collapses to a singularity • Recap: Death of Stars: Low and Medium Mass Main Sequence Star Red Dwarf Red Giant Planetary Nebula White Dwarf Black Dwarf • Death of Stars: High Mass Main Sequence Star Red Super Giant Supernova Neutron Star Black Hole • Recap: High Mass Stars: – Core size greater than 1.4x our sun • Create high mass elements such as iron – Neutron Star • Formed if remaining star is 1.4-3x sun’s mass. – Black Holes • Formed if remaining star > 3x sun’s mass Recap Video • Death of Stars: – What stars end up as depend on mass – Low and Medium mass stars • Planetary nebula --------- white dwarf – High mass stars • Supernova --------- neutron star or black hole • As fusion begins to slow down, the core of the sun will contract • Temperature in the core will rise • The outer layers of the sun will expand, consuming in the inner planets • Sun will become a Red Giant Video Link – Core of the sun will begin to fuse helium into larger elements such as carbon and oxygen – Continuing over the next 100 million years… • Core will become entirely carbon and oxygen • Core will contract • Outer layers will expand – Outer layers will form a planetary nebula • Core of sun will become a white dwarf How did it start? Gravity, gas pressure, magnetic fields, and rotation cause disk to form around protostar. Conservation of angular momentum!