Christopher | Vlad | David | Nino

SUPERMASSIVE BLACK HOLES

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 in its own Schwarzschild radius.

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)

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

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)

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

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

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 (> 1012 Lsolar )

• 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

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

WHY DO WE THINK THEY ARE BLACK HOLES?• Sphere of influence

• rh ~ GMBH/ 2 ~ 11.2(MBH/108MS)/( /200kms-1)2 pc

• Keplerian velocity 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

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

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

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

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

• 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

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

WILL SUPERMASSIVE BLACK HOLES DIE?

• Will stop growing

• Estimated terminal mass 1-10 billion Msolar

• Hawking radiation

• 30 Msolar black hole

• 1061 times current age of universe

• 100 billion Msolar black hole

• 1098 years