Copyright © 2009 Pearson Education, Inc. The other sister This is a simple one. You meet some cousins (man and wife) and you start talking to them. They tell you they have two children. What is the chance that one child is a daughter? A. 33% (1 in 3) B. 50% (50/50) C. 67% (2 in 3)Copyright © 2009 Pearson Education, Inc. The other sister This is another simple one. You meet the parents of your girlfriend. You know they have another child but you don’t know if they are a girl or boy. What is the chance that the other child is a girl? A. 33% (1 in 3) B. 50% ( 50/50) C. 67% (2 in 3)Copyright © 2009 Pearson Education, Inc. The Sister Named Florida You meet some cousins (man and wife) and you start talking to them. They tell you they have 2 children and one of them is a girl with the weird name Florida. What is the chance that the other child is a daughter? A. 33% B. 50% (50/50) C. 67%Copyright © 2009 Pearson Education, Inc. Chapter 15 Galaxies and the Foundation of Modern CosmologyCopyright © 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 M87Copyright © 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. They are generally very distant. B. They were more common early in time. C. Galaxy collisions might turn them on. D. Nearby galaxies might hold dead quasars.Copyright © 2009 Pearson Education, Inc. Thought Question All of the above! What can you conclude from the fact that quasars usually have very large redshifts? A. They are generally very distant. B. They were more common early in time. C. Galaxy collisions might turn them on. D. Nearby galaxies might hold dead quasars.Copyright © 2009 Pearson Education, Inc. Galaxies around quasars sometimes appear disturbed by collisions.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. • 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. Energy from a Black HoleCopyright © 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. • 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 quasar-like stage earlier in time. Black Holes in GalaxiesCopyright © 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 UniverseCopyright © 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. 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 Unseen InfluencesCopyright © 2009 Pearson Education, Inc. • Normal matter: ~ 4.4% — Normal matter inside stars: ~ 0.6% — Normal matter outside stars: ~ 3.8% • Dark matter: ~ 22% • Dark energy: ~ 74% Contents of UniverseCopyright © 2009 Pearson Education, Inc. 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
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