1.Astronomy Ch. 05: Stellar Evolution Sirius is a main sequence star with a small, white dwarf companion as displayed in this HST photo

2. Stellar Evolution The changes that take place in stars as they age Life cycle of stars Over millions-billions of years 3. Birthplaces Stars form out of gigantic interstellar clouds (nebulas) Famous Orion Nebula located 1500 light- years away, a region of intense star formation Orion Nebula, located in Orions Sword, appears as a greenish-cloud in telescopes 4. Orions Sword 5. A Star is Born Protostar: Star in its earliest phase of evolution; Baby star Proplyd: Protoplanetary Disk, another term for protostars and their nebular clumps 6. Protostars Protostar can be surrounded by rotating disk that will form a solar system Nuclear fusion when 10 million K internal temp Bipolar jets, material erupting into space along the axes of rotation 7. Hydrostatic Equilibrium Hydrostatic Equilibrium: Internal balance Gravity balances pressure of hot gases in star Holds star together Stars spend their lives fighting the inward crush of gravity 8. 3 Steps in Birth of a Star 1. Gravitational contraction within a cloud of gas and dust 2. Rise in interior temperature and pressure 3. Nuclear fusion begins once internal temperature reaches 10 million Kelvin 9. Protostar Diagram This artists view of a protostar displays bipolar jets 10. Beta Pictoris Circumstellar Disk; Orion Proplyd Star Beta Pictoris is surrounded by a disk of gas and dust, the nebula from which the star formed This HST image shows proplyds located in the Orion Nebula 11. Lifetimes A function of a stars mass and chemical composition High mass stars evolve fastest, low mass stars evolve slowest Stars move throughout the HR Diagram as they age; i.e., their temperatures and luminosities change over time Main Sequence stars are adults 12. Life Cycles of Stars (HR Diagram) 13. Why Stars Shine Fusion: 4 hydrogen nuclei are converted into 1 helium nuclei, excess mass is given off as energy (heat, light) Energy released by fusion can be calculated using Einsteins famous E=mc2 (E=energy, m=mass difference, c=speed of light) 14. Old Age of Stars Main sequence stars shine until all available hydrogen has been converted into helium Then the star begins to die The sun has been shining for about 5 billion years. It is middle-aged 15. Massive Stars Very massive, hot, bright stars die fastest because they use up their hydrogen rapidly; Massive stars spend only a few million years as main sequence stars. Ex: Rigel, hot, blue star in Orion Least massive, cool, dim stars such as red dwarfs can last billions of years 16. Red Giants Red giants are senior citizen stars After hydrogen fuel in core runs out, star swells into a giant Red giants are cooler and redder, they leave main sequence and enter upper right corner of HR Diagram Examples include Antares and Betelgeuse Our sun in the future 17. 5,000,000,000 AD Talk about global warming! 18. Red Giant Stars are HUGE! Ex: Betelgeuse 19. Nucleosynthesis The creation of elements in stars Main sequence hydrogen fusion Helium Fusion When red giant stars achieve 100 million K internally, helium is converted into carbon (helium flash) 20. Red Giant Nucleosynthesis Red giant stars form internal shells that produce progressively higher elements Large red giants can create heavier elements such as oxygen, aluminum, and calcium Stars can produce elements up to iron before exploding Elements higher than iron are produced in the brief explosions of stars 21. Red Giant Nucleosynthesis Each shell in the red giant produces progressively heavier elements with depth 22. Betelgeuse http://malyszp.tripod.com/stars/betelgeuse.jpg Beetle Juice (1989) was inspired by the star in Orion 23. Variable Stars Stars that change brightness in regular or irregular cycles Pulsating Variable Stars Move back and forth between the main sequence and red giant region of the HR diagram for unknown reasons Such stars vary in light output, expand and contract Ex: Cepheid variables 24. Cepheid Variables Luminous, yellow Brightness varies from 1-70 days Famous example, Delta Cephei Period-luminosity relationship, used to calculate distances 25. Cepheids: Distance Markers Period-Luminosity Relationship: For Cepheids, the longer the period of brightness change, the greater the luminosity This relationship enables the calculation of absolute magnitude. Compare absolute to apparent magnitude to estimate distance Good to about 10 million light-years (closest galaxies) 26. Delta Cephei Light Curve Delta Cephei has a roughly 5-day cycle of brightness 27. Delta Cephei Star Map Delta Cephei Delta is a naked eye star in Cepheus 28. RR Lyrae Variables Named for star RR in Lyra RR Lyrae stars are pulsating blue-white giants with periods less than 1 day Distance markers out to 600,000 ly 29. Long Period or Mira Variables Mira in Cetus, pulsating red giants Periods between 80-100 days from dim to bright Mira means the Wonderful star, proclaimed after its recognition in 1638 Mira first variable star discovered Mira brightest every 333 days 30. The Wonderful Star 31. Mira Light Curves The diagram shows the changing brightness cycle of Mira Each strip represents 15 years, and each dot represents a magnitude estimate Most of these estimates were made by amateur astronomers who do this work as part of their hobby 32. Mira -Feb 2007 In late winter, Cetus and Mira appear to be setting in the west after sunset This photo was taken in Stuttgart, Germany 33. Death of Stars Depends on mass Small stars, up to 1.4 times the suns mass, go to planetary nebula stage, fade away into dwarf stars Larger stars (8 times the suns mass) explode 34. Planetary Nebulas Type of nebula ejected by dying stars Size 0.5-1 ly in diameter Leaves behind a white dwarf star in center Famous examples: M57, the Ring Nebula in Lyra; NGC6543, Cats Eye in Draco Ring Nebula 35. M57 Ring Nebula: HST Note the central star, a white dwarf 36. Cats Eye: Amateur & HST The Cats Eye Nebula in Draco Planetary nebulas can reveal bizarre and complex shapes 37. White Dwarfs Remains after planetary nebula stage Star can no longer resist inward pull of gravity, squeezes down into an object about the size of the earth Very dense, you would weigh 35,000 times greater if you could somehow stand on a white dwarf A teaspoon of white dwarf matter would weigh over a ton Can brighten suddenly as novas 38. Ziggy 39. Black Dwarfs Gradually, the white dwarf cools, turns dull red, and shines its last energy into space White dwarf becomes a black dwarf, corpse of a star Our suns ignominious end 40. Life Stages of a Sun-Like Star 1. Protostar, gravitational contraction of gas and dust 2. Stable, main sequence star shining by hydrogen fusion 3. Evolution to red giant when helium core forms 4. Red giant, shining by helium fusion 5. Variable star, formation of carbon core 6. Planetary nebula, outer atmosphere of star ejected into space 7. White dwarf, mass packed into a star about the size of the earth 8. Dead corpse, black dwarf in space 41. Exploding Stars Stars 8 or more times greater than our sun explode Supernova: A gigantic stellar explosion (exploding star) Core of star begins fusing elements up to iron Star collapses and explodes violently Supernovas can be seen in other galaxies, sometimes even in small telescopes 42. Supernovas 100 billion times the suns luminosity for a brief moment Brief instant fuse chemical elements higher than iron on the periodic table 43. M51 Supernova (SN2005cs) Wheres the supernova? A supernova appeared in M51, a bright galaxy in Canes Venatici, in 2005 This supernova was visible in large amateur telescopes 44. Historic Supernovae 1054, Crab Nebula 1597, Tychos Star 1604, Keplers Star Supernova 1987A Tycho (top) and Kepler 45. Supernova 1987A SN1987a appeared in the Large Magellanic Cloud, a small satellite galaxy of our Milky Way that is visible from the Southern Hemisphere The supernova was positioned near the Tarantula Nebula, the large red glow in left center of the image to the right Below: Large Magellanic Cloud; Right: March 97 Time 46. 1054 Supernova, Chaco Canyon, Crab Nebula This rock art in New Mexico may depict the 1054 supernova The Crab Nebula (M1) is the remnant of the 1054 supernova 47. M1 StarMap (Taurus) The Crab Nebula is visible as a glowing patch of light in small telescopes, it is the first object in Messiers list (M1) http://www.eurekalert.org/images/release_gra Ecliptic 48. Neutron Stars From explosions of massive stars Neutron star, a type of star more massive than the sun but squeezed into a ball 10 miles across Incredibly dense 49. Pulsars Pulsars are rotating neutron stars Pulsars can send sharp, strong signals towards earth Originally thought to be alien signals (LGM) when first discovered in the 1960s Pulses range from milliseconds-4 second Pulsar found at center of the Crab Nebula 50. Black Holes Really massive stars can explode and collapse into black holes Black holes are denser than neutron stars Represent the mass of entire star shrunk into zero-radius object Gravity is so immense, even light cant escape 51. Black Hole Terms Event Horizon: Boundary of no return where no light or matter will escape Singularity: Center of black hole, a point of infinite density where the pull of gravity is infinitely strong 52. Anatomy of a Black Hole Simulated black hole, the intense gravity distorts the light of stars in the background 53. Black Hole Candidates Cygnus X-1, intense X-ray source located 8000 ly away in Cygnus Believed to be an eclipsing binary star (two stars orbiting), period 5.6 days, with unseen companion Massive black holes may exist at the center of the Milky Way and other galaxies 54. Cygnus X-1 Cygnus X-1 is located in Cygnus or the Northern Cross It is not visible in a telescope, but you can identify its general area using a star map 55. Center of Milky Way: Sgr A Sagittarius A is a radio source at the center of the Milky Way and likely marks the location of a black hole Sgr A 56. Stellar Evolution Summary Sun-like stars Protostar Main sequence star (yellow star) Red giant Planetary nebula White dwarf Black dwarf Massive Stars Protostar Main sequence (blue star) Red supergiant Supernova Neutron star or black hole (depending on mass) 57. Summary