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25. High-Energy Celestial Objects

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1 25. High-Energy Celestial Objects
Quasars are like stars with huge redshifts Ultraluminous centers of distant galaxies Active galaxies span normal galaxies & quasars Quasars, blazars, Seyferts & radio galaxies Supermassive black holes power active galaxies A unified model of active galaxies Gamma ray bursters are extremely powerful

2 Quasars: “Stars” W/Huge Redshifts
Quasi-stellar radio sources An early discovery of radio telescope technology Cygnus A Position firmly located in 1951 One of the strongest astronomical radio sources Radio luminosity ~ 107 LSun An unusual galaxy visible in the 200-inch Palomar telescope Redshifted by 5.7% Very distant by the Hubble law ~ 220 Mpc (~ 720 Mly) from Earth Spectrum has emission lines Very unusual for a galaxy Radio source 3C 48 Discovered in 1960 Another unusual galaxy visible in the 200-inch Palomar telescope Spectrum has emission lines Unidentified elements Radio source 3C 273 Discovered in 1962 Spectrum has emission lines A jet protruding from one side Problems due to a preconceived notion They are very close & have minimal redshifts

3 Breakthrough Measurements
Maarten Schmidt studies 3C Four prominent emission lines are H Balmer lines Redshifted by 15.8% Speed of ~ 45,000 km . sec–1 Distance of ~ 600 Mpc (~ 2 Bly) Greenstein & Matthews study 3C 48 Redshifted by 36.7% Speed of ~ c Distance of ~ 1,200 Mpc (~ 4 Bly) Numerous additional discoveries Radiation properties Some are “radio loud” Only ~ 10% of all quasars Others are “radio quiet” More than 200,000 quasars are now known Redshifts range from 0.06 to ~ 7.0

4 Cygnus A & Its Radio Lobes

5 Quasar 3C 273’s High-Speed Jet

6 Redshifts In 3C 273’s Spectrum

7 Redshift From UV to the Visible

8 Quasar Density Since the Big Bang

9 z: The Relativistic Redshift
z approaches ∞ as v approaches c

10 Quasars: Distant Ultraluminous Galaxies
Basic observations Most quasars are at the center of unusual galaxies Luminosities from 1038 to 1042 Watts Milky Way’s luminosity is 1037 Watts Brightest quasars are 10,000 times brighter than the Milky Way Quasar EMR properties Dominated by X-rays & g-rays Emitting material must be > 100,000 K Far too hot for any star surface High-speed gas clouds ~ 10,000 km . sec–1

11 The “Red Shift Debate” Arp et al. discover anomalous relation 1960s
Some quasars associated with low-redshift galaxies Referred to as “discordant redshifts” Disputed by many astronomers Argued that this was a line-of-sight phenomenon Resolution of the debate 1980s Observations of quasars with remote galaxies Many quasars are in groups or clusters of galaxies All have essentially identical redshifts Observations of “fuzz” around many quasars These regions exhibit stellar absorption lines Telltale signs of quasars embedded in galaxies

12 Quasar PKS 0405-123’s Radiation

13 Seyfert Galaxies Apparent anomaly Discovery of missing links
Huge energy gap between galaxies & quasars A factor of ~ 1,000 Discovery of missing links Carl Seyfert 1943 Analyzed spiral galaxies w/bright, compact nuclei Exhibit strong emission lines < 5% of most bright spiral galaxies are Seyfert galaxies > 700 Seyfert galaxies have been discovered Seyfert galaxies resemble dim, radio-quiet quasars

14 The Seyfert Galaxy NGC 7742

15 A Seyfert Galaxy at Different l’s
Visible light X-rays

16 Quasars, Blazars, Seyferts, Radio…
Quasars ~ 1,000 LMilky Way About 10% of quasars are “radio loud” Quasars emit some synchrotron radiation Blazars ~ 1,000 LMilky Way Vary in brightness over hours to months Emit intense synchrotron radiation + some radio Seyfert galaxies ~ 10 LMilky Way Resemble low-luminosity radio-quiet quasars Seyfert galaxies emit some synchrotron radiation Radio galaxies ~ 10 LMilky Way Resemble low-luminosity radio-loud quasars Elliptical galaxies midway between two radio lobes

17 Radio Galaxies Basic observations Basic properties
First discovered as peculiar galaxies 1918 Short-exposure photograph of M87 Compact nucleus w/non-polarized thermal blackbody radiation Long jet w/polarized non-thermal synchrotron radiation Often found embedded in rich galaxy clusters High probability of galactic collisions Basic properties Radio galaxies resemble dim, radio-loud quasars Normally exhibit two radio lobes in opposite directions Largest at the point farthest from the nucleus

18 Non-Thermal & Thermal Radiation

19 The center of the galaxy
The Radio Galaxy M87 The entire galaxy The center of the galaxy

20 The Radio Galaxy NGC 5128

21 Black Holes & Active Galaxies
Historical perspective Donald Lynden-Bell proposes “central engine” 1968 A supermassive black hole accreting gas & dust Much smaller in diameter than the Solar System Expected minimum size of supermassive black hole The Eddington limit of electromagnetic radiation Radiation pressure = Gravitational force Quasar 3C 273 has a luminosity of ~ LSun M3C 273 > 109 MSun The Andromeda galaxy M31 Unusual rotation curve within 5” of the galactic core Probably stars rapidly orbiting the core Highest speeds ~ 1.1” from the core ~ 110 km . sec–1 Mass ~ MSun

22 Rotation Curve of the Core of M31

23 Superluminal Motion Basic physical processes Basic observations
Nothing can travel faster than EMR in vacuum Some objects appear to be moving faster than c This is an optical illusion Basic observations Quasar 3C 273 Gas clouds are measured at speeds ~ 10 . c Smaller cloud is moving nearly along our line of sight Shorter travel time to Earth ⇒ Apparent superluminal motion

24 Superluminal Motion in 3C 273

25 Superluminal Motion Explained

26 A Unified Model of Active Galaxies
Some common properties All have high luminosity & temperature All have some radio, X-ray & synchrotron radiation A unified model of active galaxies Quasars, blazars, Seyferts & radio galaxies same Active galaxies at different angles & different stages The farther away, the earlier we see their evolutionary stage Three basic viewpoints The accretion disk is oriented edge-on to us We see a double radio source The accretion disk is oriented at a moderate angle We see either a quasar or a radio galaxy One radio lobe is oriented directly toward us We see a blazar Seyferts have consumed their accretion disks

27 A Unified Model of Active Galaxies

28 Active Galaxies: Physical Processes
Gravity near supermassive black holes Nearby stars, gas & dust drawn into the hole Original spherical distribution becomes an accretion disk Gravity & centrifugal effect balance outside event horizon Matter piles up further away from this region Abundant radio, g-ray & X-ray l’s are produced Pressure forces matter away ⊥ to accretion disk Gas is ionized & therefore constitutes an electric current This electric current in turn produces a magnetic field The magnetic field spirals outward due to rapid rotation Relativistic electrons produce synchrotron radiation Recent supportive observations Unusual appearance of the galaxy NGC 4261 An accretion disk ~ pc (~ ly) in diameter Two radio lobes ~ 2,000 pc (~ 6,400 ly) long

29 Flow Patterns Near an Accretion Disk

30 Supermassive Black Hole Jets

31 Jets & a Disk in NGC 4261

32 Gamma-Ray Bursters Basic properties Basic observations
Discovered during the late 1960s by Vela satellites Designed to detect g-rays from nuclear weapons tests Bursters randomly located in all regions of the sky Either in the galactic halo or the Universe at large Last from ~ 10–2 sec to ~ 1 hour They occur only once Basic observations The Italian-Dutch BeppoSAX satellite Very good angular resolution of about 1 arcminute 28 February 1997 BeppoSAX’s first burster A visible-light “afterglow” was observed 8 May 1997 BeppoSAX’s second burster Afterglow had z = They are extremely far away Most distant burster had z = 4.51

33 Source of Gamma-Ray Bursters
Recent observations They are not at the core of their host galaxies Unlikely to be the flare-up of an active galaxy They are within their host galaxies An extraordinary event Possible explanations Energy is released in the formation of a black hole Two merging neutron stars A hypernova An exceptionally energetic supernova

34 Table 25-1: Redshift & Distance

35 Important Concepts Quasars Seyfert galaxies Radio galaxies Blazars
~ 1,000 times brighter than a galaxy Only 10% are actually “radio loud” Seyfert galaxies Low-luminosity radio-quiet quasars Emit some synchrotron radiation Radio galaxies Low-luminosity radio-loud quasars Elliptical galaxies between two lobes Blazars Emit intense synchrotron radiation Brightness varies in hours to months Explained by active galaxies Three different perspectives Double radio sources Quasars & radio galaxies Seyfert galaxies may be old quasars Supermassive black holes Probable source of intense radiation Accretion disk channels matter in Centrifugal effect stops some matter Plasma channeled away along axis Probable collision of galaxies Gamma-ray bursters Brief one-time events Not in the host galaxy core Possibly formation of black holes Two neutron stars merge A hypernova

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