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