Chapter 15 Galaxies and the Foundation of Modern Cosmology Copyright 2009 Pearson Education Inc 15 4 Quasars and Other Active Galactic Nuclei Our goals for learning What are quasars What is the power source for quasars and other active galactic nuclei Do supermassive black holes really exist Copyright 2009 Pearson Education Inc What are quasars Copyright 2009 Pearson Education Inc If the center of a galaxy is unusually bright we call it an active galactic nucleus Quasars are the most luminous examples Active Nucleus in M87 Copyright 2009 Pearson Education Inc The highly redshifted spectra of quasars indicate large distances From brightness and distance we find that luminosities of some quasars are 1012LSun Variability shows that all this energy comes from a region smaller than the solar system Copyright 2009 Pearson Education Inc Thought Question What can you conclude from the fact that quasars usually have very large redshifts A B C D They are generally very distant They were more common early in time Galaxy collisions might turn them on Nearby galaxies might hold dead quasars Copyright 2009 Pearson Education Inc Thought Question What can you conclude from the fact that quasars usually have very large redshifts A B C D They are generally very distant They were more common early in time Galaxy collisions might turn them on Nearby galaxies might hold dead quasars All of the above Copyright 2009 Pearson Education Inc Galaxies around quasars sometimes appear disturbed by collisions Copyright 2009 Pearson Education Inc Quasars powerfully radiate energy over a very wide range of wavelengths indicating that they contain matter with a wide range of temperatures Copyright 2009 Pearson Education Inc Radio galaxies contain active nuclei shooting out vast jets of plasma that emit radio waves coming from electrons moving at near light speed Copyright 2009 Pearson Education Inc The lobes of radio galaxies can extend over hundreds of millions of light years Copyright 2009 Pearson Education Inc An active galactic nucleus can shoot out blobs of plasma moving at nearly the speed of light The speed of ejection suggests that a black hole is present Copyright 2009 Pearson Education Inc Radio galaxies don t appear as quasars because dusty gas clouds block our view of their accretion disks Copyright 2009 Pearson Education Inc Characteristics of Active Galaxies Luminosity can be enormous 1012LSun Luminosity can rapidly vary comes from a space smaller than solar system They emit energy over a wide range of wavelengths contain matter with wide temperature range Some drive jets of plasma at near light speed Copyright 2009 Pearson Education Inc What is the power source for quasars and other active galactic nuclei Copyright 2009 Pearson Education Inc The accretion of gas onto a supermassive black hole appears to be the only way to explain all the properties of quasars Copyright 2009 Pearson Education Inc Energy from a Black Hole The gravitational potential energy of matter falling into a black hole turns into kinetic energy Friction in the accretion disk turns kinetic energy into thermal energy heat Heat produces thermal radiation photons This process can convert 10 40 of E mc2 into radiation Copyright 2009 Pearson Education Inc Jets are thought to come from the twisting of a magnetic field in the inner part of the accretion disk Copyright 2009 Pearson Education Inc Do supermassive black holes really exist Copyright 2009 Pearson Education Inc Orbits of stars at center of Milky Way stars indicate a black hole with mass of 4 million MSun Copyright 2009 Pearson Education Inc Orbital speed and distance of gas orbiting center of M87 indicate a black hole with mass of 3 billion MSun Copyright 2009 Pearson Education Inc Black Holes in Galaxies Many nearby galaxies perhaps all of them have supermassive black holes at their centers These black holes seem to be dormant active galactic nuclei All galaxies may have passed through a quasarlike stage earlier in time Copyright 2009 Pearson Education Inc Galaxies and Black Holes The mass of a galaxy s central black hole is closely related to the mass of its bulge Copyright 2009 Pearson Education Inc Galaxies and Black Holes The development of a central black hole must somehow be related to galaxy evolution Copyright 2009 Pearson Education Inc What have we learned What are quasars Active galactic nuclei are very bright objects seen in the centers of some galaxies and quasars are the most luminous type What is the power source for quasars and other active galactic nuclei The only model that adequately explains our observations holds that supermassive black holes are the power source Copyright 2009 Pearson Education Inc What have we learned Do supermassive black holes really exist Observations of stars and gas clouds orbiting the centers of galaxies indicate that many galaxies perhaps all of them have supermassive black holes Copyright 2009 Pearson Education Inc Chapter 16 Dark Matter Dark Energy and the Fate of the Universe Copyright 2009 Pearson Education Inc 16 1 Unseen Influences in the Cosmos Our goals for learning What do we mean by dark matter and dark energy Copyright 2009 Pearson Education Inc What do we mean by dark matter and dark energy Copyright 2009 Pearson Education Inc Unseen Influences Dark matter An undetected form of mass that emits little or no light but whose existence we infer from its gravitational influence Dark energy An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate Copyright 2009 Pearson Education Inc Contents of Universe Normal matter 4 4 Normal matter inside stars 0 6 Normal matter outside stars 3 8 Dark matter Dark energy Copyright 2009 Pearson Education Inc 22 74 What have we learned What do we mean by dark matter and dark energy Dark matter is the name given to the unseen mass whose gravity governs the observed motions of stars and gas clouds Dark energy is the name given to whatever might be causing the expansion of the universe to accelerate Copyright 2009 Pearson Education Inc 16 2 Evidence for Dark Matter Our goals for learning What is the evidence for dark matter in galaxies What is the evidence for dark matter in clusters of galaxies Does dark matter really exist What might dark matter be made of Copyright 2009 Pearson Education Inc What is the evidence for dark matter in galaxies Copyright 2009 Pearson Education Inc We measure the mass of the solar system
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