AST 115 1st Edition Lecture 33 Outline of Last Lecture I. Some methods of determining distancesII. Redshifts in the Spectra of GalaxiesIII. The Hubble LawIV. The “Look – Back” PrincipleV. QuasarsOutline of Current Lecture I. Quasars continuedII. Active GalaxiesIII. Types of Active Galaxiesa. Seyfert Galaxiesb. Double – Lobbed (radio) Galaxyc. Jet GalaxiesIV. The Power Source of Quasars and AGNV. Gravitational LensesCurrent Lecture Quasars continued:o If we suppose this active region occurs in the nucleus of a very distant galaxy and apply the Look – Back Principle, we decided that… Quasars must be the hyperactive centers of very distant, very very young galaxies. Active Galaxieso Active galaxies: those that have bright nuclei associated with great energy production or energetic outflows of matter. Most emit strong radio waves and have also been called “radio galaxies”. Astronomers usually call them AGN for “active galactic nuclei”. Types of Active Galaxieso Seyfert Galaxies: spiral galaxies with a bright star – like nuclei, and strong emission lines in their spectra.o Double Lobbed (Radio) Galaxy: two regions of strong radio emission occur on either side of a “peculiar” galaxy. (Peculiar means the galaxy does not fit well intoHubble’s classification scheme). Ex: Cygnus AThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Jet Galaxies: stream of material projects from the center of a galaxy. The stream is emitting radio waves, sometimes light and other wavelengths like x – rays. Ex: M87o Observations of these active galaxies imply that some unknown object exists at the center of the galaxies or quasar and acts as the power source. The Power Source of Quasars and AGNo Thousands of quasars have now been discovered, but only 10% are strong radio emitters. Some call them QSO “Quasi – Stellar Object” They are all very luminouso The power source must be prodigious, yet contained in a small volume of space.o The accretion disks of supermassive black holes are believed to be the power source of quasars. (No radiation can be emitted from the black hole itself).o The accretion disk funnels energetic particles out along the two polar directions, at right angles to the disk. These produce two strong “jets” or beams.o If we see the jets nearly face on, it is perceived as a quasar. If we see the jets at other angles, we perceive active galaxies with a jet, or else double – lobbed radioemission.o Hubble Space Telescope images of some QSOs show the peripheries of the younggalaxies, with their very bright nuclei, confirming the model. Gravitational lenseso Quasars produce very bright and very narrow beams of light; they can be used to test Einstein’s General Relativity.o Spacetime should be curved in the vicinity of dense concentrations of matter. Light from a distant quasar could be deflected as it passes by a massive galaxy or cluster of galaxies billions of LY away on its way to us.o Einstein’s “rings”, “crosses”, and “arcs” have been detected, confirming his prediction of the curvature of spacetime in the vicinity of compact
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