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Star_Form_Evolforclass

Star_Form_Evolforclass - How do Stars and Planets form and...

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How do Stars and Planets form and evolve? Astr 2340 Spring 2010 R. Chandar
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Stellar Evolution Stars are like people in that they are born, grow up, mature, and die. A star’s mass determines what life path it will take (and how it will die). We will divide all stars into three groups: Low Mass (0.08 M < M < 2 M ) Intermediate Mass (2 M < M < 8 M ) High Mass (M > 8 M ) The H-R Diagram makes a useful roadmap for following stellar evolution (coming up in a few slides).
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Note how much the luminosity of stars varies compared with their masses. This plot shows about a factor of 100 in mass (0.2 to 20 solar masses). But the luminosities vary by a factor of 100 million for the same range of masses (0.01 to 1,000,000 solar luminosity) Relationship between the mass of a star and its Luminosity 1 M_sun = 1 L_sun 0.2 M_sun = 0.01 L_sun 10 M_sun = 10,000 L_sun •The luminosity of a star reflects it mass. Stars with more mass are intrinsically brighter, & those with lower mass are fainter
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A star is born with a limited supply of core hydrogen. This means that it can’t stay in the core-hydrogen burning (Main sequence phase) indefinitely. Stars spend most of their lives on the main sequence. Like the masses of stars, the lifetimes of stars change steadily as we move up the main sequence. The most massive stars have much SHORTER main sequence lifetimes than less massive stars Massive stars have a much larger supply of H to start with, but they fuse H to He so quickly that finish up their fuel faster. A 10 solar mass star has a luminosity of 10,000 times the sun. So it is burning through its fuel 10,000 times faster than the sun, but only has 10x as much fuel to deal with. Lives only 1/1000th as long as the sun LIFETIMES ALONG THE MAIN SEQUENCE:
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Stellar Lifetimes • 90 % of star’s life spent in main sequence Lifetime depends on mass
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-- we determine a star’s surface temperature directly from its spectrum or color. Stars with hotter surface temps appear bluer than those with cooler temps. (They are also brighter, but that has to be measured separately). -- In principle, all that is needed is to measure the amount of light output by a star in the red and the blue portions of the electromagnetic spectrum. Red/cool stars will put out more energy in the red, and Blue/hot stars will put out more energy in the blue -- they will have different ‘colors’ Surface Temperature of Stars
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The Hertzsprung-Russell Diagram Low Mass High Mass
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Stages of Star Formation on the H-R Diagram
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Stellar Evolution The life of any star can be described as a battle between two forces: Gravity vs. Pressure Gravity always wants to collapse the star. Pressure holds up the star. Remember Newton’s Law of Gravity the amount of gravitational force depends on the mass gravitational potential energy is turned into heat as a star collapses
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Populations of Stars Population I – young, recently formed stars. Contain more metals than older stars, as they were created from debris from previous stellar explosions.
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