Active GalaxiesGuiding QuestionsQuasars look like stars but have huge redshiftsSlide Number 4Slide Number 5Slide Number 6About 10% of all quasars are strong sources of radio emission and are therefore called “radio-loud”; the remaining 90% are “radio-quiet”Slide Number 8Some of quasars’ energy is synchrotron radiation produced by high-speed particles traveling in a strong magnetic fieldQuasars are the ultraluminous centers of distant galaxiesSeyfert galaxies seem to be nearby, low-luminosity, radio-quiet quasarsRadio galaxies are elliptical galaxies located midway between the lobes of a double radio sourceRelativistic particles are ejected from the nucleus of a radio galaxy along two oppositely directed beamsSlide Number 14Slide Number 15Seyferts and radio galaxies bridge the gap between normal galaxies and quasarsSlide Number 17Quasars, blazars, Seyferts, and radio galaxies are active galaxiesS u p e r l u m i n a l M o t i o nSlide Number 20Slide Number 21Supermassive black holes are the “central engines” that power active galactic nucleiSlide Number 23Slide Number 24Quasars, blazars, and radio galaxies may be the same kind of object seen from different anglesAn observer sees a radio galaxy when the accretion disk is viewed nearly edge-on, so that its light is blocked by a surrounding torusSlide Number 27Slide Number 28Gamma-ray bursters produce amazingly intense flashes of radiationBy observing the afterglow of long-duration gamma-ray bursters, astronomers find that these objects have very large redshifts and appear to be located within distant galaxiesThe bursts are correlated with supernovae, and may be due to an exotic type of supernova called a collapsarJargon1Active Galaxies2Guiding Questions1. Why are quasars unusual? How did astronomers discover that they are extraordinarily distant and luminous?2. What evidence showed a link between quasars and galaxies?3. How are Seyfert galaxies and radio galaxies related to quasars?4. How can material ejected from quasars appear to travel faster than light?5. What could power the incredible energy output from active galaxies?6. Why do many active galaxies emit ultrafast jets of material?7. What are gamma-ray bursters? How did astronomers discover how far away they are?3Quasars look like stars but have huge redshiftsThese redshifts show that quasars are several hundred megaparsecs or more from the Earth, according to the Hubble law456• To be seen at such large distances, quasars must be very luminous, typically about 1000 times brighter than an ordinary galaxy7About 10% of all quasars are strong sources of radio emission and are therefore called “radio-loud”; the remaining 90% are “radio-quiet”89Some of quasars’ energy is synchrotron radiation produced by high-speed particles traveling in a strong magnetic field10Quasars are the ultraluminous centers of distant galaxies11Seyfert galaxies seem to be nearby, low-luminosity, radio-quiet quasarsSeyfert galaxies are spiral galaxies with bright nuclei that are strong sources of radiation12Radio galaxies are elliptical galaxies located midway between the lobes of a double radio source13Relativistic particles are ejected from the nucleus of a radio galaxy along two oppositely directed beams141516Seyferts and radio galaxies bridge the gap between normal galaxies and quasars17• Blazars are bright, starlike objects that can vary rapidly in their luminosity• They are probably radio galaxies or quasars seen end-on, with a jet of relativistic particles aimed toward the Earth18Quasars, blazars, Seyferts, and radio galaxies are active galaxies• Quasars, blazars, and Seyfert and radio galaxies are examples of active galaxies• The energy source at the center of an active galaxy is called an active galactic nucleus (AGN)• Rapid fluctuations in the brightness of active galaxies indicate that the region that emits radiation is quite small19S u p e r l u m i n a l M o t i o n202122Supermassive black holes are the “central engines” that power active galactic nuclei• The evidence suggests that an active galactic nucleus consists of a supermassive black hole onto which matter accretes• As gases spiral in toward the supermassive black hole, some of the gas may be redirected to become two jets of high-speed particles that are aligned perpendicularly to the accretion disk232425Quasars, blazars, and radio galaxies may be the same kind of object seen from different angles26An observer sees a radio galaxy when the accretion disk is viewed nearly edge-on, so that its light is blocked by a surrounding torus27• At a steeper angle, the observer sees a quasar• If one of the jets is aimed almost directly at the Earth, a blazar is observed2829Gamma-ray bursters produce amazingly intense flashes of radiation• Short, intense bursts of gamma rays are observed at random times coming from random parts of the sky• The origin of short-duration gamma-ray bursters is unknown30By observing the afterglow of long-duration gamma-ray bursters, astronomers find that these objects have very large redshifts and appear to be located within distant galaxies31The bursts are correlated with supernovae, and may be due to an exotic type of supernova called a collapsar32Jargon• accretion disk• active galactic nucleus (AGN)• active galaxy• blazar• collapsar• double radio source• Eddington limit• gamma-ray burster• head-tail source• nonthermal radiation• polarized radiation• quasar• radio galaxy• radio lobes• Seyfert galaxy• superluminal motion• supermassive black hole• thermal