black&holes&and&quasars& - astronomy group...

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

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

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

2

2

2

22121

cGMr

rGMmmc

rGMmmv

S

S

=

=

=

r s

Types of Black Hole •  Normal

–  Formed from massive stars going supernovae

•  Super-‐massive –  Formed in galaxy cores during iniAal collapse?

•  Most galaxies are believed to harbour a super-‐massive black-‐hole in their cores –  Existence of Intermediate Mass Black Holes uncertain

!MM 10~BH

!" MM 97

BH 10~

Evidence for SMBHs •  We find that stars have velociAes of >110km/s within 2.5pc of

the core of M31

Super-massive BH in M31 •  IF they are in circular orbits we can use the Virial theorem to

calculate the mass inside r

•  In our Milky Way galaxy –  Velocities > 1000 km/s inside 0.01 pc!

•  => 2 x 106 Msun SMBH

!

"

#=#=

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MM

M

637CORE

11

16232

CORE

108.6104.11067.6

1035.2)10110(

kgGrv

Our Galactic Centre

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

–  Teff ~ 20,000 K –  Burst of star formaAon 107 years ago?

•  Or masses modified by star-‐star collisions? –  Plus repeated bursts in the past (AGB stars present) –  Stellar density ~> 106 stars pc–3 –  Compare solar neighbourhood: stellar density ~ 0.1 stars pc–3

–  Use stars to study kinemaAcs –  And mass of central object

GRvM

RGMv

22 =!=

Time lapse movie of Galactic Centre over past 12 years

Orbital Motions

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:

( ) constant 5.0constant 2 !<"! pcrMRv

Obs.Tech.

i.e., Keplerian

Central Black Hole •  Mass of central object

•  Mass within 0.01 pc is ~3 x 106 Msun •  Keplerian velociAes inside of 0.5 pc

•  Mass within 10 pc is ~3 x 107 Msun •  mass density is ~4 x 106 Msun pc-‐3

•  So, does this necessarily mean a black hole? •  If not, mass density is ~4 x 1012 Msun pc-‐3

–  Cluster of neutron stars?

GRvM2

=

Mass distribution

106

mass

107

105

Radius (pc)

0.01 0.1 1.0 10.0

Msun

4 x 106 Msun pc-3 4 x 1012 Msun pc-3

3 x 106 Msun

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 < 105 Lsun

•  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 Rsun

R = GMc2

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’

Galaxies – AS 3011 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


NGC5548 (Seyfert I) NGC3277 (Normal Spiral)

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


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


OpAcal jet

3C273

Typical Quasar or QSO spectrum

Steep conAnuum Broad lines No discernable host galaxy

point-‐like.


ObservaAons -‐> ProperAes Point-‐like = compact Distant = luminous Broad lines = high velociAes High excitaAon lines = energeAc Variable = small (<1 lyr)


at 1 Gpc

Oten have associated jets visible in raAo due to relaAvisAc charged material zipping out along open field lines: Synchrotron radiaAon Jets oten extend 10-‐500kpc!

24

Emit over all wavelengths:, e.g.,Mk421

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

-  BL Lacs (BL Lacertae)=no features -  OVV (OpAcally violently variable)

LINERS -  Weak Seyferts (no broad lines)

Theories Two compeAng theories:

-  Nuclear starbursts -  Super-‐massive black holes

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: vorbit ~ (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 RS = 2 G Mbh / c2 (≈ 3 km x Mbh / Msolar)

•  However SMBHs as central mechanism only adopted following discovery of the GC SMBH and that in M31 and M84 which also exhibits a jet

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

(not to scale!)

see Seyfert 1

see Seyfert 2

narrow line region clouds at ~0.1-‐1 kpc

broad line region

accreAon torus

can also see polarized light from near the nucleus if scavered

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AGN Unification

Seyfert 2 galaxy

Seyfert 1 galaxy

Quasar Blazar

Jet !!!

Torus

Antonucci, 1993

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CorrelaAon between SMBH mass and bulge velocity dispersion

CorrelaAon between SMBH mass and Bulge Absolute magnitude

AGN acAvity much more common in the past. Consistent with bulge formaAon preceeding disc formaAon

AGN ac+vity

The Cosmic Star-‐formaAon History

Constructed from measurements of Hα or UV fluxes at various redshits

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

CSFH v AGN acAvity v Time

.

.

.

37

Puxng it together ? Dark Maver Baryonic Maver 0yrs 5Gyrs

13Gyrs

Rapid merging

Slow merging

SMBHs AGN

BULG

ES

DISKS

P-‐BU

LGES

??

COLLAPSE/MERGERS

INFALL

SECULAR

ACCE

LERA

TING DEC

ELER

ATING

U

AGN acAvity

AGN no longer acAve

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