HOW TO DETECT A BLACK HOLE

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HOW TO DETECT A BLACK HOLE

• Effects on matter/light outside the horizon
• gravitational attraction of other bodies
• dark star with mass
• distinguish from normal star, white dwarf,
  neutron star
• Accretion (swallowing) of gas
• gas heated by compression/turbulence in strong
  gravity field X-rays
• but need a source of gas
• accretion from interstellar matter insignificant
• mass transfer in binaries to the rescue

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CAN WE IMAGE BLACK HOLES?
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CAN WE IMAGE BLACK HOLES?
NOT YET, BUT SOMEDAY?

• HUBBLE read newspaper _at_ 1 mile
• Optical/UV telescope in space
• Falls short by 100,000
• VLBA read newspaper in Philly
• Transcontinental radio telescope
• Falls short by 1,000
• MAXIM Read newspaper on moon
• X-ray interferometer in space
• Can do it! Ready for launch (?) 2020-2030

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• MAXIM
• Micro-
• arcsecond
• X-ray
• Imaging
• Mission

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HOW TO DETECT BLACK HOLES
1. Mass of compact companion in close binary
system (stellar remnants only)
X-ray binary (artists impression)
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HOW TO DETECT BLACK HOLES
M87 disk
2. Orbital motion of stars or gas clouds
(supermassive holes)
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HOW TO DETECT BLACK HOLES
3. Random motions of stars in galaxys nucleus
(supermassive holes)
Globular cluster M3 (similar appearance to a
galactic nucleus)
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Gas almost never falls directly into a black hole
Too much swirl (angular momentum)
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Gas almost never falls directly into a black hole
Too much swirl (angular momentum)
makes it more like a whirlpool
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ACCRETION DISK

• Like a flattened whirlpool
• Gas must give up angular momentum to go down the
  drain
• VISCOSITY (FRICTION)

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ACCRETION DISKS ALLOW US to PROBE the HORIZON
Energy flows from one form to another...

• GRAVITY
• MOTION
• HEAT
• RADIATION (X-rays, UV)

matter swirling inward
friction
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ENERGY FLOW IN ACCRETION DISK
Energy flows from one form to another...

• GRAVITATIONAL POTENTIAL ENERGY
• KINETIC ENERGY
• HEAT
• RADIATION

falling matter
compression/turbulence
particle collisions, etc.
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EVOLUTION OF CLOSE BINARIES

• Algol Paradox and its resolution
• Roche lobe sphere of influence
• actually teardrop shaped
• Matter flows across Lagrange point
• Too much angular momentum
  

ACCRETION DISK
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ALGOLS CAN EVOLVE INTO X-RAY BINARIES

• Crucial that mass ratio flips
• otherwise stars can fly apart
• Compact star either NS or BH
• depends on mass of precursor
• Two modes of mass transfer
• stellar wind star smaller than Roche lobe
• Roche lobe overflow star swells to fill Roche
  lobe

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BINARY MASS FUNCTION depends on...

• Orbit period easy
• Doppler shift of normal star easy
• Mass of normal star hard
• Orbit inclination hard

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100
0.1
1
Log Mass (solar units)
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NEUTRON STAR VS. BLACK HOLE how to tell

• BH if
• mass (reliable)
• distinctive spectrum (unreliable ????)
• NS if
• pulsing (X-ray pulsar)
• evidence of nuclear explosions on surface (X-ray
  burster)

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X-ray pulsar (accretion)
X-ray burster (thermonuclear)