Black Holes and Quasars

Transcription

1 Black Holes and Quasars Black Holes Normal and Super- massive The Schwartzchild Radius (event horizon) Normal and Super Massive Black Holes (SMBHs) The GalacAc Centre (GC) The Black Hole in Andromeda AcAve GalacAc Nuclei (AGN) Discovery of Seyferts and Quasars Basic properaes Blazars, QSOs, BL Lacs, OVVs, LINERs etc. AGN UnificaAon SMBH correlaaons with host galaxy AGN AcAvity with Cosmic Time ImplicaAons for galaxy formaaon

2 Black Holes Gravity is the curvature of space-time by matter. If sufficient mass exists in a small enough volume space-time is distorted such that even light cannot escape

3 The Schwarzschild Radius The radius at which even light cannot escape is known as the event horizon or Schwarzschild radius. For a non- rotaang black hole this is simply when the KineAc Energy = GravitaAonal Energy for a photon r s r S mv mc = 2 2 = = 2GM 2 c GMm r GMm r S

4 Types of Black Hole Normal Formed from massive stars going supernovae Super- massive MBH ~ 10M! Formed in galaxy cores during iniaal collapse? M 7 " 9 BH ~ 10 M! Most galaxies are believed to harbour a super- massive black- hole in their cores Existence of Intermediate Mass Black Holes uncertain

5 Evidence for SMBHs We find that stars have velociaes of >110km/s within 2.5pc of the core of M31

6 Super-massive BH in M31 IF they are in circular orbits we can use the Virial theorem to calculate the mass inside r M M CORE CORE v r (110# 10 ) # 2.5# 3# 10 = = " 11 G 6.67# = 1.4# 10 kg = 6.8# 10 M! 16 In our Milky Way galaxy Velocities > 1000 km/s inside 0.01 pc! => 2 x 10 6 M sun SMBH

7 Our Galactic Centre

8 Infrared Studies Infrared (2 µm) penetrates through the dust Can use to probe stellar populaaons and dynamics in GC Find central cluster of young massive stars T eff ~ 20,000 K Burst of star formaaon 10 7 years ago? Or masses modified by star- star collisions? Plus repeated bursts in the past (AGB stars present) Stellar density ~> 10 6 stars pc 3 Compare solar neighbourhood: stellar density ~ 0.1 stars pc 3 Use stars to study kinemaacs And mass of central object v 2 = GM R! M = 2 v R G

9 Time lapse movie of Galactic Centre over past 12 years

10 Orbital Motions

11 Proper Motions in Galactic Centre Measured by speckle and (now) adapave opacs In IR (2.2 mm) to see through dust Speckle: many short exposures Freeze out effects of turbulence in atmosphere Add coherently to see image! Measures velociaes of many stars near GN From velociaes: mass At 0.01 pc: v ~ 1000 km/s At 0.04 pc: v ~ 500 km/s ImplicaAon: Obs.Tech. v 2 R! constant " M pc ( r < 0.5 )! constant i.e., Keplerian

12 Central Black Hole Mass of central object M = 2 v R G Mass within 0.01 pc is ~3 x 10 6 M sun Keplerian velociaes inside of 0.5 pc Mass within 10 pc is ~3 x 10 7 M sun mass density is ~4 x 10 6 M sun pc - 3 So, does this necessarily mean a black hole? If not, mass density is ~4 x M sun pc - 3 Cluster of neutron stars?

13 Mass distribution mass 10 7 M sun 3 x 10 6 M sun x M sun pc -3 4 x 10 6 M sun pc Radius (pc)

14 Sgr A* Radio source in centre of nucleus Molecular gas disc rotates around it Stellar cluster centred on it What is it? Variable non- thermal radio source Luminosity < 10 5 L sun Size: 0.3 mas ~ 2.4 AU!!! Could be a neutron star But it doesn t move!!! Should be in equilibrium with stellar cluster! v < 200 km/s Most probably a black hole Schwarschild radius ~ ~ few R sun R = GM c 2

15 Flare from black hole x- ray flare from central locaaon Due to mass falling into the GC super- massive black hole Heats up and emits in X- rays before crossing event- horizon

16 Quasars & Seyferts 1943 Carl Seyfert publishes a list of odd galaxies: Mostly spirals with point- like nuclei Broad emission lines Also high ionisaaon states (O[VI]) Doppler interpretaaon implied >1000 km/s Later two classes of Seyferts proposed: Seyfert Is: Broad hydrogen lines, narrow forbidden lines (e.g., O[III]) Seyfert IIs: Only narrow lines present Assumed lines originate from disanct regions: Broad lines from Broad Line Region Narrow lines from Narrow Line Region Galaxies AS

17 NGC5548 (Seyfert I) NGC3277 (Normal Spiral) Galaxies AS

18 Seyfert 1 showing both Broad and Narrow line features Seyfert 2 showing narrow lines only Images of both show a spiral galaxy with a very bright central nucleus 18

19 Discovery of Quasars - Strong radio sources known to correlate with point- like objects - Maarten Schmidt collected the first spectrum for radius source 3C273 - Contained unexplained broad lines, idenafied as redshited hydrogen - Eventually deduced a redshit of 0.16 (Schmidt, Nature, 1963) - Soon other Quasars were discovered with redhists upto 2 - Current record holder around z=6.0 Galaxies AS

20 3C273 OpAcal jet Galaxies AS

21 Typical Quasar or QSO spectrum Steep conanuum Broad lines No discernable host galaxy point- like.

22 ObservaAons - > ProperAes Point- like Distant = compact = luminous Broad lines = high velociaes High excitaaon lines = energeac Variable = small (<1 lyr) Galaxies AS

23 Oten have associated jets visible in raao due to relaavisac charged material zipping out along open field lines: Synchrotron radiaaon Jets oten extend kpc! Galaxies AS at 1 Gpc

24 Emit over all wavelengths:, e.g.,mk421 24

25 Other AGN types Quasars, radio- loud QSO (Quasi- stellar objects), radio quiet Seyfert I(Broad lines) Seyfert II(Narrow lines) Blazers (Highly variable systems), superluminous LINERS - BL Lacs (BL Lacertae)=no features - OVV (OpAcally violently variable) - Weak Seyferts (no broad lines) 25

26 Galaxies AS

27 Two compeang theories: - Nuclear starbursts - Super- massive black holes Theories

28 Evidence for black holes Gas moving at ~10,000 km/s, inconsistent with stellar orbits Emission lines change in brightness over days to weeks light travel Ame implies emission from region only ~ light- weeks across (~0.01 pc) Hence must have very high density, because fast orbits within very small region: v orbit ~ (G M / r) 1/2 Only a black hole can pack this much maver in so densely the power is generated at a few Schwartzschild radii R S = 2 G M bh / c 2 ( 3 km x M bh / M solar ) However SMBHs as central mechanism only adopted following discovery of the GC SMBH and that in M31 and M84 which also exhibits a jet 28

29 unified model The several types may be the same kind of object seen from different angles (Unified Model) see narrower lines if a spectrum comes from gas orbiang further out fastest stuff is in an accreaon disk around the black hole broad line region narrow line region clouds at ~0.1-1 kpc accreaon torus (not to scale!) 29 see Seyfert 1 see Seyfert 2 can also see polarized light from near the nucleus if scavered

30 AGN Unification Antonucci, 1993 Blazar Quasar Seyfert 2 galaxy Torus Seyfert 1 galaxy 30 Jet!!!

31 CorrelaAon between SMBH mass and bulge velocity dispersion 31

32 CorrelaAon between SMBH mass and Bulge Absolute magnitude

33 AGN ac+vity AGN acavity much more common in the past. Consistent with bulge formaaon preceeding disc formaaon

34 The Cosmic Star- formaaon History Constructed from measurements of Hα or UV fluxes at various redshits

35 CSFH v AGN AcAvity AGN acavity does not seem to trace SFH at high- z 1. Data uncertain 2. Redshit axis misleading..lets switch to Ame à

36 CSFH v AGN acavity v Time...

37 Puxng it together? ACCELERATING DECELERATING U Dark Maver 0yrs 5Gyrs 13Gyrs?? Rapid merging Slow merging AGN acavity AGN no longer acave Baryonic Maver SMBHs AGN COLLAPSE/MERGERS BULGES INFALL DISKS P- BULGES SECULAR 37