Supermassive black holes

1. Supermassive black holes Christopher | Vlad | David | Nino

2. What is a black hole? • Massive object from which nothing can escape. • Even light is attracted by gravity. • Schwarzschild radius is the distance for a given mass where the escape velocity is the speed of light • A black hole has its entire mass enclosed inits own Schwarzschild radius.

3. How can we see black holes? • No light escapes • Hawking Radiation • Not observed • Accretion disks • Observed radiation An artist's rendering of the Cygnus X-1 system. (from http://spaceart1.ning.com/photo/cygnus-x1)

4. How do black holes form? • Type II Supernova of a massive star • Collapse of a neutron star • Nothing can stop it • Don’t know what happens after

5. How do we weigh black holes? • Mass can be inferred from orbital velocities of stars around it The position of a star around the Supermassive Black Hole Sgr A* (from http://www.sciencemag.org)

6. Properties of SUPERMASSIVE BLACK HOLES • Masses range from millions to billions of solar masses • Located at center of most galaxies • Especially flat, normal galaxies with bulge component • Active SMBHs emit energetic jets • X-Rays and Gamma rays • Perpendicular to accretion disks (possibly) along rotation axis • Limit star growth by clearing gas along their axis

7. PROPERTIES OF SUPERMASSIVE BLACK HOLES • Strong X-Ray emitters • Account for half of radiation after Big Bang • SMBH rotation drags spacetime in direction of rotation (Roy Kerr) – “frame dragging” • Local phenomenon • Can delay matter falling in due to sideways motion • Weaker tidal forces than BH of regular size/mass • Since larger surface area of event horizon

8. Eating or fasting? Different faces of SMBHs • SMBHs may regulate galactic growth along with appetite for matter • Saggitarius A* - dormant SMBH in Milky Way nearly empty • Very little matter in immediate surroundings • Large amounts of matter in surroundings • Quasar galaxies, Seyfert galaxies, Blazar galaxies • Quasar galaxy • Most variably-luminous objects in universe (> 1012Lsolar) • Powerful jets powered by accretion disk around SMBH • Central SMBH 10,000x times regular black hole • 3C 273 – first quasar discovered early 1960s • Quasar activity peaked in early universe

9. Eating or fasting? Different faces of SMBH • Seyfert galaxy • Produce spectral emissions from highly ionized gas • Large amounts of IR, UV, X-Ray rad. • Jet velocity 500-4,000 km/s • Central SMBH mass 108 Msolar • Blazar galaxy • Emission jets pointed towards Earth • Radiation spectrum radio to Gamma rays • Variable / Unstable output • At 9 billion ly can be detected with Earthly instruments • SMBHs key for early universe • Facilitate formation of galaxies

10. Why do we think they are black holes? • Sphere of influence • rh ~ GMBH/2 ~ 11.2(MBH/108MS)/( /200kms-1)2pc • Keplerianvelocity distribution near galactic center • Must be highly concentrated mass at center • Proper motion of stars in Milky way indicate singularity at galactic center • Called Sagittarius A* • Higher concentration than normal of 22Ghz water masers imply an AGN in NGC 4258

11. Other Methods • Hubble Space Telescope high resolution images • Shows clearly gas or stellar dynamics at galactic nucleus • Only works if gravity is most influential force on gas • Reverberation or Echo mapping • Only for type 1 active galactic nuclei • Can probe regions up to 1000 times the Schwarzschild Radius

12. How does the SMBH relate to the surrounding galaxy? • MBH vs. blue luminosity of the bulge (whole galaxy if elliptical) • Correlates to blue luminosity from the bulge • Generally scattered correlation; less so for ellipticals • Latest relation given by log(MBH) = (8.37±0.11) – (0.419±0.085)(B0T + 20.0) • MBH vs. velocity dispersion, (σ) • σ relates to LB, which relates to MBH • Tighter correlation than mass vs. bulge light; maybe more fundamental • Latest relation (MBH/108MSun) = (1.66±0.24)(σ/200km s-1)4.68±0.43

13. Other Correlations with host galaxy • MBH vs. bulge light concentration (C) • Tight correlation; little scattering • Practical relation; needs only one measurement • Depends on parametric characterization of light profile • MBH vs. Dark Matter Halo • σ correlates tightly with large scale circular velocity distribution • Less massive halos are less efficient at forming SMBH • (MBH/108MSun) ~ 0.10(MDM/1012MSun)1.65

14. How do Supermassive Black holes form? • What came first? • Supermassive Black Holes or galaxies ? • Proponents of galalxies first: • Observed galaxies without SMBH (ex. NGC 2613) • Bulge component in flattened normal galaxies necessary

15. Proponents of SMBH first: • Uniform density shown by microwave background radiation • Not sufficiently clumped to form SMBH from regular matter alone • Suggest SMBH from dark matter • Quasar activity peaked 10 billion years ago • Primordial seed theory • Central black hole can double its mass every 40 million years

16. Growth of Supermassive Black Holes • Stellar and intermediate mass black holes gravitate towards galactic center • Coalesce there to SMBH (ex. NGC 253) • Major growth from galactic collisions and mergers • Example collision of Milky Way with Andromeda in 5 billion years • New Black Hole: 100 million Msolar • Both from SMBH mergers and influx of material

18. will supermassive black holes die? • Will stop growing • Estimated terminal mass 1-10 billion Msolar • Hawking radiation • 30 Msolar black hole • 1061times current age of universe • 100 billion Msolar black hole • 1098 years