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Insert: Beyond our Solar System Deployment of the Hubble Space Telescope in Earth orbit, April 24, 1990 The 300-meter radio telescope at Arecibo, Puerto Rico Hertzsprung-Russell diagram Shows the relation between stellar Brightness (absolute magnitude) and Temperature Diagram is made by plotting (graphing) each star's Luminosity (brightness) and Temperature Hertzsprung-Russell diagram Parts of an H-R diagram Main-sequence stars • 90% of all stars • Band through the center of the H-R diagram • Sun is in the main-sequence Giants (or red giants) • • • • Very luminous Large Very large giants are called supergiants Only a few percent of all stars Hertzsprung-Russell diagram Parts of an H-R diagram White dwarfs • • • • • Fainter than main-sequence stars Small (approximate the size of Earth) Lower-central area on the H-R diagram Not all are white in color Perhaps 10% of all stars Hertzsprung-Russell diagram The Orion Nebula is a well-known emission nebula A faint blue reflection nebula in the Pleiades star cluster Stellar evolution Two opposing forces in a star are Gravity – contracts Thermal nuclear energy – expands Stages Birth Main-sequence stage • 90% of a star's life is in the main-sequence Red giant stage Burnout and death • white dwarf, neutron star, or a black hole Evolutionary stages Stellar evolution Stellar remnants White dwarf Small and Dense • Spoonful weighs several tons Neutron star Gravitational force collapses atoms • Electrons combine with protons to produce neutrons • Pea size sample weighs 100 million tons • First one discovered in early 1970s Crab nebula (remnant of an A.D. 1054 supernova) Crab Nebula in the constellation Taurus Stellar remnants Black hole More dense than a neutron star Intense surface gravity lets no light escape As matter is pulled into it • Becomes very hot • Emits x-rays Likely candidate is Cygnus X-1, a strong x-ray source Binary Pair with a Red Giant and a Black Hole Galaxies Other galaxies Existence was first proposed in mid-1700s by Immanuel Kant Four basic types of galaxies • Spiral galaxy • Arms extending from nucleus • About 30% of all galaxies • e.g., Milky Way Face-on view of the Milk Way Galaxy Edge-on view of the Milk Way Galaxy Great Galaxy, a spiral galaxy, in the constellation Andromeda Galaxies Other galaxies Four basic types of galaxies • Barred spiral galaxy • Elliptical galaxy • Irregular galaxy The study of light Doppler effect The apparent change in wavelength of radiation caused by the relative motions of the source and observer Used to determine • Direction of motion • Increasing distance – wavelength is longer ("stretches") • Decreasing distance – makes wavelength shorter ("compresses") The Doppler effect Red shifts Doppler effect Change in the wavelength of light emitted by an object due to its motion • Movement away stretches the wavelength • Light appears redder • Movement toward “squeezes” the wavelength • Light shifted toward the blue Expanding universe Most galaxies exhibit a red Doppler shift Raisin bread analogy of an expanding universe Big Bang theory Accounts for galaxies moving away from us Universe was once confined to a "ball" that was Supermassive Dense Hot Big Bang theory Big Bang marks the inception of the universe Occurred about 15 billion years ago All matter and space was created Matter is moving outward Fate of the universe Two possibilities • Universe will last forever • Outward expansion sill stop and gravitational; contraction will follow Big Bang theory Fate of the universe Final fate depends on the average density of the universe • If the density is more than the critical density, then the universe would contract • Current estimates point to less then the critical density and predict an ever-expanding, or open, universe End of Chapter 16