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The Birth of Stars & Stellar Evolution
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Stellar Lifecycles The process by which stars are _______ and use up their fuel. What exactly happens to a star as it uses up its fuel is strongly dependent on the star’s ______. formed mass The Orion Nebula - Birthplace of stars
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Stellar Evolution Stars are like people in that they: _______, ____, ____, and ____. A star’s mass determines its life path. We will divide all stars into three groups: ____ Mass (0.08 M < M < 8 M) __________ Mass (8 M < M < 25 M) _____ Mass (M > 25 M) develop born age die Low Intermediate High
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Stellar Evolution The life of any star can be described as a battle between two forces: _______ vs. ________ Gravity always wants to _______ the star ________ holds up the star Gravity Pressure collapse Pressure
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Star Nurseries Interstellar Clouds __ and ___
Relatively high densities Gravitational collapse Create a denser region, will become _________ H He protostar
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Hubble Space Telescope
A Star is Born! This animation is from the Hubble Space Telescope archive and is in the public domain. For policy statement see: Movie. Click to play. Eagle Nebula Hubble Space Telescope Pleiades
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Star Formation As the protostar collapses, angular momentum is conserved the protostar rotates faster matter falling in to the protostar flattens into a (protostellar) disk
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Bi-Polar Jets
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Direct Evidence of Disks & Jets
disk formation
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Star Formation As the ________ heats up, enough thermal energy is radiated away from surface to allow collapse to continue. energy is transported to surface first via _________ as core gets even hotter, transport via _________ takes over ______ reactions begin when _____ reaches __________________ protostar convection radiation Fusion core 107 K (10,000,000 K)
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Stages of Star Formation on the HR Diagram
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Arrival on the Main Sequence
The _____ of the protostar determines: how ____ each phase will last ______ the new-born star will land on the MS i.e., what spectral type mass long where
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The Main Sequence (MS) _____ of all stars lie on the _____ ________!
90% main sequence
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BRIGHT HOT COOL FAINT
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Stellar Luminosity Classes
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Missing the Main Sequence
mass < 0.08 M If the protostar has a ______________: It does not contain enough gravitational energy to reach a core temperature of 107 K _________ occurs, star is “stillborn”! We call these objects _____________. They are very faint, radiate their thermal energy in the infrared, and have cores made of Hydrogen _____ are in between ______________ No fusion Brown Dwarfs Sizes planets and stars
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The First Brown Dwarf Discovery
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_____________ Evolution Main Sequence
Stars start their lives on the Main Sequence with approximately ____ H and ____ He. Main Sequence 75% 25% H-He envelope In the center: H “burns” to He: the fraction of He goes up to maintain the pressure the core contracts the temperature goes up the rate of energy generation increases Core “burning” H to He
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Stellar Evolution The structure of the Sun has been changing continuously since it settled in on the main sequence. The Hydrogen in the core is being converted into Helium.
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Stellar Evolution Stars begin to evolve off the zero-age main sequence from day 1. Compared to 4.5 Gyr ago, the radius of the Sun has increased by 6% and the luminosity by 40%. 4.5Gyr ago Today
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Leaving the Main Sequence
The core begins to collapse H shell heats up and H fusion begins outer layers of the star expand the star is now in the _______ phase of its life subgiant
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Red Giants The He core collapses until it heats to 108 K - ______________ ( He C) He fusion begins The star, called a ________, is once again stable. Red giants create/release most of the __ of organic molecules (and life) Red Giant C
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Low Mass Main Sequence Stars
When the Red Giant exhausts its He fuel the C core collapses. ____ mass stars don’t have enough gravitational energy to heat to 6 x 108 K (temperature at which Carbon fuses) Low The star overcomes gravity the outer envelope of the star is gently blown away this forms a ______________ This animation is from the Hubble Space Telescope archive and is in the public domain. For policy statement see: Planetary Nebula
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Planetary Nebulae
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Planetary Nebulae In low-mass stars the core never gets hot enough to ignite Carbon-burning. However, the rate of He-burning in the shell source is unstable, so the star pulsates and the envelope of the star is ejected in a _______________. The core of the star remains behind as a ___________ star that gradually cools. planetary nebula white dwarf
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Planetary Nebulae Cat’s Eye Nebula Twin Jet Nebula
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The collapsing Carbon core becomes a ___________ White Dwarf
Planetary Nebulae Ring Nebula Hourglass Nebula The collapsing Carbon core becomes a ___________ White Dwarf
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______ 1,000,000 grams/cm3 1 Ford SUV/cm3
White Dwarfs Small - _______ = Earth’s Radius Hot - Temperature typically 10,000’s K Radius ______ 1,000,000 grams/cm3 Ford SUV/cm3 Dense
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White Dwarfs and Black Dwarfs
Most remnants remain white dwarfs for millions of years. Once the star has burned all fuels it becomes a __________, which has no radiation at all. Black dwarf Several white dwarfs located in the M4 globular cluster.
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Summary of Post-Main-Sequence Evolution of Sun-like Stars
Core collapses; outer shells bounce off the hard surface of the degenerate C core Formation of a Planetary Nebula C core becomes degenerate Fusion stops at formation of C core. M < 4 Msun Red dwarfs: He burning never ignites M < 0.4 Msun
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The Death of a Middle Mass Star
A middle mass star is any star with a mass between _________ solar masses. Temperatures reach levels high enough to form ____ The core becomes a __________, releasing a shockwave/explosion called a _________. These remnants, all between ____________ _______ are neutron stars. 8 and 25 iron neutron star supernova 1.4 and 3 solar masses
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Massive Star Evolution
The critical difference between low and high-mass star evolution is the core temperature. In stars with M>8Mo the central temperature is high enough to fuse elements all the way to Iron (Fe)
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Supernova The explosion can ________ the combined light of a galaxy!
______________ are formed in the material blown off the star. These elements can be used to form planets and new stars. Depending on its mass the core may become a __________ or collapse further to a __________. outshine Heavy elements neutron star black hole
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Tycho’s Supernova (X-rays)
Supernovae Tycho’s Supernova (X-rays) exploded in 1572 Veil Nebula
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Historical SN 1006, 1054, 1181, 1572, 1604 and 1658 were years when bright `guest stars’ were widely reported
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Historical SN Point a modern telescope in the direction of all “guest stars” and see a rapidly-expanding shell of material. In two cases, the remnant was discovered before the historical event
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Historical SN The 1054AD event was so bright it cast shadows during the day -- this is the position of the Crab Nebula
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Neutron stars are usually between 20 and 30 kilometers in diameter
Neutron stars are usually between 20 and 30 kilometers in diameter. These stars are __________ and spin very fast. No _____________. They __________ out of their magnetic poles because they are spinning so quickly. Neutron Stars very dense visible radiation emit X-rays A neutron star with X-rays being emitted from the magnetic poles.
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_______ are a form of neutron stars that instead of emitting a constant signal of X-ray, will only ____ ______. The escaping X-rays sweep around such as a light beam sweeps around a __________. Pulsars Pulsars emit pulses lighthouse A pulsar emitting pulse X-rays.
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Death of a High Mass Star
over 25 solar Any star that has a mass of __________ ______ will begin its death the same way that a middle mass star would. They will follow the same death pattern up to the supernova. The difference is that the remnant left behind from a high mass star is _______________________. This makes it too large to stop the gravitational contraction at any point. So the remnant continues to collapse and a _________ is born. masses greater than 3 solar masses black hole
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Schwarzschild’s Equation
Karl Schwarzschild came up with his idea of a black hole radius. This radius is also known as the _____ _______. The event horizon provides an effective size for a black hole because nothing can escape from within it. event horizon The event horizon of a black hole.
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Black holes have _____________ and no size, they are a _________.
The singularity is considered to be at the center of the black hole. ____________ - a flat disk of matter spiraling into a black hole. Sometimes this matter originated from a companion star. infinite density The Black Hole singularity Accretion disk an accretion disk spiraling a black hole.
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At first the victim would only feel as if s/he were falling
At first the victim would only feel as if s/he were falling. But as s/he fell closer to the singularity tidal forces would cause _______________ where the part of the body closest to the singularity would begin to stretched faster than the other parts because of gravitational force. The body is then stretched out like a noodle. Falling In spaghettification spaghettification of an astronaut.
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This is the most common theorized black hole.
Stellar Black Holes This is the most common theorized black hole. These black holes have between __ _______ times the mass of our sun. Black holes ____ __________ by our eyes. Possible Light Flash from Black Hole Collision Spotted 3 and 20 can not be seen a black hole with companion star.
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Supermassive Black Holes
A ________________ ____ may be a million or more solar masses. A recent find says that massive black holes may be at the ______ ______________, possibly even fueling them. hole center of many galaxies interpretation of a supermassive black hole.
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Supermassive Black Hole
In elliptical galaxy NGC 4889 300 million ly away in Coma cluster. 21 billion times the mass of the sun. Ours is 4 million solar masses.
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White Dwarf Red Giant Planetary Nebula Interstellar Cloud Main Sequence Star Evolution of a Low Mass Star Interstellar Cloud Big Main Sequence Star Red Giant Type II Supernova Neutron Star Black Hole Evolution of a High Mass Star
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You can read more about Stellar Evolution by clicking on the link below.
You might have to exit out of PPT after you click on the link to view the chapter. 25.2 Stellar Evolution - American Academy
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If the previous slide doesn’t work, you can read more about Stellar Evolution by copying the link below and pasting it into your browser. The link should say 25.2 Stellar Evolution - American Academy
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http://www.physics.sfasu.edu/markworth/ast105/256,1,Stellar Evolution
25 13 Holes and Stellar Evolution on the Main Sequence Birth of Stars & Stellar Evolution
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