Black holes

Black holes

This lecture is part of the course "physics of active galactic nuclei" offered to graduate students in astrophysics by Rodrigo Nemmen and Joao Steiner at IAG USP.

https://rodrigonemmen.com/teaching/active-galactic-nuclei/

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Rodrigo Nemmen

May 20, 2016
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  1. 2.

    Hazard+14 Optical image of 3C 273 3C273, the first Quasar

    7 Figure 6. The culmination of the Parkes positions and the Palomar redshift. 3C273 had become: eve tern he w ligh of c hav him and On tha also Ha tha Thu star hig obj was the per Qu in a Soc and tan app oth rep the The are Maarten Schmidt was the fi rst to recognize that quasars are ultra- luminous distant objects. After Cyril Hazard and his colleagues in Australia had pinned down the position of the radio source 3C 273, Schmidt took a spectrum of the starlike object in that location. The unusual features of the spec- trum could be understood only if there was a 16 percent redshift, implying an enormous distance. Schmidt has, over the past 40 years, continued to discover and study distant quasars. He has been a leader in analyzing how the quasar population depends on redshift (or cosmic epoch), as described in Chapter 9. mber 29 he managed to obtain a spectrum of the “star” that was not over- which showed some faint emission lines, but with no obvious explanation y expected stellar lines. yed until February 6th, as outlined in the paper presented to the American Society (Schmidt, 2011). He wrote: d on 6 February 1963. In response to Hazard’s letter I decided to have at the spectra... For reasons that I don’t remember I tried to construct an iagram. When the energy levels did not come out regularly spaced, I was check on the regularity of the observed lines, I decided to compare them er lines of hydrogen... Specifically, I took for each line in 3C 273 the ratio gth over the wavelength of the nearest Balmer line. The first ratio was 1.16, s... also 1.16. ruck me that I might be seeing a redshift. When the third and fourth ratios e to 1.16, it was abundantly clear that I was seeing in 3C 273 a redshifted um.” ed fortunate that the 3C273 redshift was small enough that the Balmer re and would be readily recognised. aarten Schmidt’s 200” spectrum taken on the night of December 29, with the
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    Quasars in the centers of distant galaxies (z>1) outshine all

    stars in the host galaxy this image: z ~ 0.2 d L ~ 1 Gpc Hubble Space Telescope Bahcall+97
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    THE ASTROPHYSICAL JOURNAL, 479:642È658, 1997 April 20 1997. The American

    Astronomical Society. All rights reserved. Printed in U.S.A. ( HUBBL E SPACE T EL ESCOPE IMAGES OF A SAMPLE OF 20 NEARBY LUMINOUS QUASARS1 JOHN N. SOFIA AND DAVID H. BAHCALL, KIRHAKOS, SAXE Institute for Advanced Study, School of Natural Sciences, Princeton, NJ 08540 AND DONALD P. SCHNEIDER Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 Received 1996 August 21; accepted 1996 November 8 ABSTRACT Observations with the Wide-Field Camera of the Hubble Space Telescope (HST ) are presented for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These obser- vations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (two), apparently normal ellipticals (10), apparently normal spirals with H II regions (three), complex systems of gravitationally interacting components (three), and faint surrounding nebulosity (two). The quasar host galaxies are centered on the quasar to the accuracy of our measure- ments, 400 pc. There are more radio-quiet quasars in galaxies that appear to be ellipticals (seven) than in spiral hosts (three), contrary to expectations. However, three, and possibly Ðve, of the six radio-loud quasars have detectable elliptical hosts, in agreement with expectations. The luminous quasars studied in this paper occur preferentially in luminous galaxies. The average absolute magnitude of the hosts is 2.2 mag brighter than expected for a Ðeld galaxy luminosity function. The superb optical characteristics of the repaired HST make possible the detection of close galactic companions; we detect eight companion galaxies within projected distances of 10 kpc from quasar nuclei. The presence of very close companions, the images of current gravitational interactions, and the higher density of galaxies around the quasars suggest that gravitational interactions play an important role in triggering the quasar phenomenon. Subject headings: galaxies: clusters: general È galaxies: interactions È galaxies: structure È quasars: general 1. INTRODUCTION Figures and (Plates 25È28) tell the main story of this 1 2 paper. We urge the reader to look at these beautiful HST images before continuing with the text and the quantitative details. point-spread function (PSF), there are small, quantitative di†erences between the results described in this paper and previous results we have reported. In the previous work, we used a stellar PSF determined from a red standard star, F141. In the present work, we have used stellar PSFs that ABSTRACT Observations with the Wide-Field Camera of the Hubble Space Telescope (HS representative sample of 20 intrinsically luminous quasars with redshifts smaller t vations show that luminous quasars occur in diverse environments that include the brightest cluster galaxies (two), apparently normal ellipticals (10), apparently n regions (three), complex systems of gravitationally interacting components (three), nebulosity (two). The quasar host galaxies are centered on the quasar to the acc ments, 400 pc. There are more radio-quiet quasars in galaxies that appear to be el spiral hosts (three), contrary to expectations. However, three, and possibly Ðve, quasars have detectable elliptical hosts, in agreement with expectations. The lumin this paper occur preferentially in luminous galaxies. The average absolute magnit mag brighter than expected for a Ðeld galaxy luminosity function. The superb optical characteristics of the repaired HST make possible the dete companions; we detect eight companion galaxies within projected distances of nuclei. The presence of very close companions, the images of current gravitationa higher density of galaxies around the quasars suggest that gravitational interacti role in triggering the quasar phenomenon. Subject headings: galaxies: clusters: general È galaxies: interactions È galaxies: st quasars: general 1. INTRODUCTION Figures and (Plates 25È28) tell the main story of this 1 2 paper. We urge the reader to look at these beautiful HST images before continuing with the text and the quantitative details. We summarize in this paper the results of our analysis of HST -WFPC2 observations of a representative sample of 20 point-spread function (PSF di†erences between the resu previous results we have rep used a stellar PSF determ F141. In the present work, were obtained for four se cussion in of the PSFs c ° 4 The visual appearanc 1996).
  5. 6.

    The pioneers of the theory of supermassive black holes applied

    to AGNs: Salpeter, Zeldovich, Lynden-Bell Chapter 5 fueled by the transfer of gas from the companion star onto the compact remnant, the massive black holes in AGN would be fueled through the capture of gas from the surrounding galaxy, or even by the swallowing of entire stars. This captured debris would swirl downward into the intense gravitational fi eld, reaching nearly the speed of light before it is swallowed. The gravitational energy thus liberated would provide the power for both the luminosity and the outfl owing gaseous jets that char- acterize AGN. Lynden-Bell also predicted that the modern-day galaxies that had once hosted quasars should still contain their black hole relics. Evidence for these quiescent black holes now abounds (Chapter 8), pro- viding perhaps the strongest vindication of the black hole paradigm. Modeling Quasars Salpeter Zeldovich Lynden-Bell
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    Powerful, relativistic jets from galactic nuclei Signs of Activity to

    a precision of a few arcseconds, by noting the time at which it was occulted by the Moon. They had to make special adjustments to the telescope to observe something as far north – and consequently as close to the horizon – as 3C 273. (“3C” denotes the third Cambridge catalog of radio sources – the source had been discovered by means The Very Large Array in New Mexico reveals the double-lobed radio structure of Cygnus A in rich detail. The energy produced in the nucleus is carried to the lobes by jets, the traces of which are Remain aligned for millions of years (what is the gyroscope?)
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    0 0 −30 30 −60 60 −90 90 −120 120

    −150 150 −180 180 30 −30 60 −60 90 −90 90 Ackermann+15, 1501.0605 Gamma-ray sky observed by Fermi LAT is dominated by blazars FSRQs: flat spectrum radio quasars BL Lac objects AGNs of unknown type non-blazar AGNs
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    SUPERMASSIVE BLACK HOLE OF M87 581 sitions of the slit

    during the observations compared with the Ha ] N II image of the M87 disk from the WFPC2 archive. The gray levels are d 40% of the nuclear peak in the outer region. The nucleus has been rescaled to be displayed within this range of values. North is up and east is n, geometric distortion is also induced on the slit and dispersion directions by the spectrographic mirror and the distortion in the dispersion direction was determined by tracing the spectra of two stars taken in the core of the globular cluster. These stars are ^130 pixels apart and almost at the opposite extremes of the slit. The distortion t direction was determined by tracing the brightness distribution along the slit of the planetary nebula NGC 6543 es. Ground-based observations (Perez, Cuesta, Axon, & Robinson, in preparation) indicate that the distortion TABLE 1 LOG OF OBSERVATIONS Integration Time Target Data Set Date (1996) (s) Format Description M87 . . . . . . . . . . . . . X3E40101T Jul 25 297 1024 ] 512 Interactive acq. M87 . . . . . . . . . . . . . X3E40102T Jul 25 2169 1024 ] 512 Spectrum =POS1 M87 . . . . . . . . . . . . . X3E40103T Jul 25 600 1024 ] 512 Internal Ñat M87 . . . . . . . . . . . . . X3E40104T Jul 25 600 1024 ] 512 Internal dark M87 . . . . . . . . . . . . . X3E40105T Jul 25 2169 1024 ] 512 Spectrum 1 =NUC M87 . . . . . . . . . . . . . X3E40106T Jul 25 600 1024 ] 512 Internal Ñat M87 . . . . . . . . . . . . . X3E40107T Jul 25 2169 1024 ] 512 Spectrum =POS2 M87 . . . . . . . . . . . . . X3E40108T Jul 25 600 1024 ] 512 Internal Ñat M87 . . . . . . . . . . . . . X3E40109T Jul 25 2597 1024 ] 512 Spectrum 2 =NUC M87 . . . . . . . . . . . . . X3E4010AT Jul 25 600 1024 ] 512 Internal Ñat M87 . . . . . . . . . . . . . X3E4010BT Jul 25 2597 1024 ] 512 Spectrum 3 =NUC M87 . . . . . . . . . . . . . X3E4010CT Jul 25 600 1024 ] 512 Internal Ñat M87 . . . . . . . . . . . . . X3E4010DT Jul 25 2597 1024 ] 512 Spectrum 4 =NUC No. 2, 1997 SUPERMASSIVE BLACK HOLE OF M87 FIG. 12.ÈBest Ðts of the observed rotation curve with the Keplerian thin disk model. The solid line corresponds to cpix \ 22 km s~1 and the dotted line to cpix \ 22.7, 1.73 ] 109 M _ , h \ 0¡ .7, i \ 49¡V sys \ 1204 b \ 0A .06, M BH (sin i)2 \ 1.68 ] 109 M _ km s~1 (s 2 \ 1.73). The residuals are computed for the former set of values and the error bars on the velocity are the square ro 1274 eq. (9). Macchetto+97, ApJ Keplerian rotation curve Kinematics of gaseous disk in giant elliptical galaxy M87 mapped with HST M = 3 ⇥ 109 M v = r GM r
  10. 16.

    VLBA radio observations of water maser in NGC 4258: thin

    gas disk following Keplerian motion Kormendy & Ho 2013, ARA&A M = 3.6 ⇥ 107 M Myioshi+95, Nature Observer’s view Top view High Bowl 0.1 pc 0.1 pc –1 1,200 1,000 800 600 0 0 20,000 40,000 NGC 4258 Keplerian rotation curve 60,000 80,000 1 2 3 4 Impact parameter (mas) r/rS (km s–1) 5 6 7 8 9 Redshifted masers Blueshifted masers Systemic masers a b ded by Universidade de Sao Paulo (USP) on 04/30/15. For personal use only. 2-Kormendy ARI 24 July 2013 12:27 Observer’s view Top view High Bowl 0.1 pc 0.1 pc –1 1,200 1,000 800 600 400 200 0 0.1 0.2 0.3 0.0 0 0 20,000 40,000 NGC 4258 Keplerian rotation curve 60,000 80,000 1 2 3 4 Impact parameter (mas) r/rS r (pc) Velocity (km s–1) 5 6 7 8 9 Redshifted masers Blueshifted masers Systemic masers a b
  11. 17.

    VLBA radio observations of water maser in NGC 4258: thin

    gas disk following Keplerian motion
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    10 light-days = 260 billion km Ghez, Schödel, Genzel et

    al. central mass = 4 million solar masses Resolved stellar dynamics around Our Galactic Center with Keck observations
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    black hole Our Galactic Center hosts the nearest supermassive black

    hole: Sagittarius A* Ghez, Schödel, Genzel et al. central mass = 4 million solar masses 10 light-days = 260 billion km
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    Using stars as test particles to probe the central mass:

    stellar kinematics van den Bosch+12, Nature relation16 predicts a black-hole mass of 2.4 3 109M8 , so the measured value is almost one order of magnitude higher, or a 2.1-s.d. outlier relative to the intrinsic scatter in the M. –s relation1. Apart from NGC 1277, NGC 4486B9 and to lie significantly above the relations, and a known to lie significantly below the relatio know if these over-massive and under-mass the tails of a relatively narrow distribution o properties, or if they demonstrate non-un more black-hole measurements, including th pact galaxies with high velocity dispersions, w the cause of the black-hole/galaxy connectio –300 –200 –100 0 100 200 300 V (km s–1) a 17 × 109M O black hole 1 × 108M O black hole NGC 1277 100 200 300 400 σ (km s–1) Seeing b –0.2 0.0 0.2 h 3 c –6 –4 –2 0 2 4 6 x (kpc) –0.2 0.0 0.2 d . . h 4 we construct a three-dimensional luminous-mass model of the stars by 107 108 109 1010 1011 Black-hole mass (M O ) NGC NGC 4486B Ref. 8 Ref. 19 Ref. 16 Mass–luminosity . Modeling: Disentangle gravitational contribution of host galaxy vs central “invisible” mass Every galaxy with a bulge has a supermassive invisible object in its center
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    60 80 100 200 300 400 Velocity dispersion / km

    s-1 106 107 108 109 1010 M BH / M sun Elliptical / classical bulge Pseudo-bulge , AGN , Quiescent Galaxies somehow coevolve with their central black holes: the M-σ relation Woo+13 central black hole host galaxy property
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    Schimoia, …, Nemmen+12 The Astrophysical Journal, 748:145 (12pp), 2012 April

    1 Schimoia et al. Figure 1. Acquisition image from 2010 August 15, where we illustrate the locations of the 1. ′′0 × 1. ′′0 extraction windows for the nucleus and stellar population spectra. The square labeled A represents the nuclear extraction window, while squares B and C represent the extranuclear ones, from which we obtained the spectrum of the underlying stellar population. (A color version of this figure is available in the online journal.) continuum to the corresponding value at the nucleus) thus Figure 2. Observation from 2010 August 15. Top: nuclear spectrum (region A of Figure 1). Middle: stellar population obtained from averaging the spectra from regions B and C in Figure 1. Bottom: nuclear spectrum after the subtraction of the stellar population. blue continuum we need the FC continuum to contribute with at least 15%–20% of the flux at 5800 Å. We thus can say that a possible FC contribution to the nuclear spectrum is lower than 20% of the continuum flux at 5800 Å. We consider this value an upper limit, as a comparison between the stellar continuum from our spectra and the AGN continuum obtained in the work of Nemmen et al. (2006) shows that the stellar continuum in our FWHM ≈ 10000 km/s center distance of the ring (from 1 ¼ 1300 to 450) could lead to the observed increase in the separation of the two peaks, R ÀB . Such a dramatic change in the physical loca- tion of a given volume of gas could not occur on a timescale of 5 yr, however, as we noted in x 4.1. Rather, the emission properties of the ring must have changed, so that the radius of maximum emission became smaller. Therefore, to pro- duce a self-consistent and physically plausible scenario for the entire set of observations, we were led to revise the model parameters. This revision represents a refinement of earlier models, which is possible only after following the variability of the line profile over a baseline of 10 yr. We now propose that the ring has always had a smaller inner radius of 1 ¼ 450 (and now resembles a disk more than a ring) and that the increasing width of the profile is due to a change in emissivity such that, in more recent epochs, the inner regions of the disk make a more significant relative contribution to the total line emission. This picture is also consistent with the observational result that the flux of the broad line is decreasing, as discussed above. To explain the increasing separation between the two peaks, we experimented with several emissivity laws. We found that we could best reproduce the observations with a broken power law, such that inside a radius q the power- law index is q1 ¼ À1 and outside this radius q2 ¼ 1. This means that the emissivity increases with radius from 1 to q and then decreases with radius beyond q. These q-values are also physically motivated: in the ‘‘ saturation ’’ region, the increase in emissivity is due to the increase in the area of the ring, while beyond q, the decrease can be understood as due to both the drop-off in the intensity of the radiation field as rÀ2 and the increase of the emitting area as r. In this parameterization of the disk emissivity, varying the ‘‘ break radius ’’ q allows us to reproduce the shifts of the blue and red peaks. In particular, allowing the break radius to decrease with time shifts the region of maximum emission closer to the center and results in an increase in the separation between the two peaks. At the same time, since 2 Nov. 91 5 Oct. 92 5 Jan. 94 6 Dec. 94 24 Jan. 96 24 Sep. 97 6400 6600 6800 0 1 2 3 4 Fig. 7.—Fits of the elliptical-disk model to the profiles from 1991 November to 1997 September obtained by changing only 0 (the orientation of the disk relative to the line of sight) and q (the radius of the peak of the emissivity law). The values of these parameters are listed in Table 3. Storchi-Bergmann, Nemmen+03 Broad, mildly relativistic emission lines in the optical
  17. 24.

    Tanaka+95, Nature Broad, relativistic velocities from X-ray emission lines: produced

    within a few Schwarzschild radii FWHM ≈ 100.000 km/s
  18. 29.

    s of light rays become rved close to the a

    black hole. As the pproached, a light be aimed within an y narrow cone in order ing dragged into the Schwarzschild radii a med light beam can ack hole indefi nitely. zon, the escape cone no light rays emit- is radius can avoid ed into the black hole. rom just outside the ild radius would reach bserver with a large nd a clock near the hole ear to run slow. Begelman & Rees
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    Thorne Radii of different objects with M = 1.2 MSun.

    Black holes are the most compact objects in nature white dwarf neutron star black hole
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    -1.0 -0.5 0.0 0.5 1.0 j = a M 1.0

    1.2 1.4 1.6 1.8 2.0 R+ Event horizon radius as a function of spin
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    Kerr black holes drag space around them within a region

    called ergosphere frame-dragging or Lense-Thirring effect
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    UO aim o 0.2 0.5 0.7 0.6 0.9 0.95 0.96

    1 mO. (3.12) Fig.3.2. Efficiency of energy release by gas accreting through a thin accretion disk onto a spinning black hole. The quantity plotted is 1 - em. as a function of the hole angular efficiency of energy release Blandford
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    20 40 60 80 100 0.15 0.20 0.25 Circular speed

    M = 108 Msun vK/c R/RS Schwarzschild black hole
  28. 46.

    A cloud of interstellar gas is rotating slowly around its

    axis and contracting because of the attractive pull of its own gravity. As the cloud collapses, it rotates faster. The gas in the cloud’s equatorial plane moves inward more slowly because its rotation starts to balance the gravity. Gas above and below the plane falls inward much faster. Gravitational contraction Rotation Faster contraction Slower contraction galaxy. In general, galaxies do not tic collisions and mergers compli- At least some elliptical galaxies, as of spiral galaxies, may have arisen m in binary star systems when one compact, dense white dwarf) grav- companion (usually a larger, less considerable angular momentum otion of the two stars around their it typically cannot fall directly in- arf. Instead the gas ends up form- . ch shorter year than Earth—a mere nner parts of a disk invariably takes bit than does material in the outer al periods causes shear: bits of ma- stances from the center of the disk ox on page 54]. If some form of fric- erial, it tries to slow down the more s and speed up the more slowly or- ar momentum is therefore trans- outer regions of the disk. As a con- ner regions loses rotational support ard. The overall result is a gradual he central star or black hole. to the innermost orbit of an accre- avitational potential energy. Some into giving the material the faster ls inward; the rest is dissipated into y by the friction itself. Thus, the ma- very hot, emitting copious amounts ay radiation. The energy release can dable power sources. A cloud of interstellar gas is rotating slowly around its axis and contracting because of the attractive pull of its own gravity. As the cloud collapses, it rotates faster. The gas in the cloud’s equatorial plane moves inward more slowly because its rotation starts to balance the gravity. Gas above and below the plane falls inward much faster. Gravitational contraction Rotation Faster contraction Slower contraction of the stars (for example, a compact, dense white dwarf) grav- itationally pulls gas off its companion (usually a larger, less compact star). This gas has considerable angular momentum from the original orbital motion of the two stars around their common center of mass, so it typically cannot fall directly in- ward toward the white dwarf. Instead the gas ends up form- ing a disk around the dwarf. Just as Mercury has a much shorter year than Earth—a mere 88 days—the material in the inner parts of a disk invariably takes less time to complete one orbit than does material in the outer parts. This gradient in orbital periods causes shear: bits of ma- terial at slightly different distances from the center of the disk slide past one another [see box on page 54]. If some form of fric- tion is present in the disk material, it tries to slow down the more rapidly orbiting inner regions and speed up the more slowly or- biting outer regions. Angular momentum is therefore trans- ported from the inner to the outer regions of the disk. As a con- sequence, material in the inner regions loses rotational support against gravity and falls inward. The overall result is a gradual spiraling of matter toward the central star or black hole. As material spirals down to the innermost orbit of an accre- tion disk, it must give up gravitational potential energy. Some of the potential energy goes into giving the material the faster orbital speed it gains as it falls inward; the rest is dissipated into heat or other forms of energy by the friction itself. Thus, the ma- terial in the disk can become very hot, emitting copious amounts of visible, ultraviolet and x-ray radiation. The energy release can make accretion disks formidable power sources. This phenomenon is what first alerted astronomers to the ex- istence of black holes. Black holes themselves cannot emit light, but the accretion disks around them can. (This general statement ignores the theorized Hawking radiation, an emission that would be undetectable for all but the smallest black holes and JIAN A cloud of interstellar gas is rotating slowly around its axis and contracting because of the attractive pull of its own gravity. As the cloud collapses, it rotates faster. The gas in the cloud’s equatorial plane moves inward more slowly because its rotation starts to balance the gravity. Gas above and below the plane falls inward much faster. Rotation Faster contraction Slower contraction Blaes, SciAm