Download The Big Four:

HOW TO DETECT A BLACK HOLE
• Effects on matter/light outside the horizon
– gravitational attraction of other bodies
– “dark star” with mass  3M Sun
• 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
CAN WE IMAGE BLACK HOLES?
CAN WE IMAGE BLACK HOLES?
…NOT YET, BUT SOMEDAY…?
• HUBBLE: read newspaper @ 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
200
M
MAXIM =
Microarcsecond
X-ray
Imaging
Mission
CONSTELLATION
BORESIGHT
Hub Spacecraft
10
KM
COLLECTOR
SPACECRAFT
(32 PLACES
EVENLY SPACED)
CONVERGER
SPACECRAFT
5000
KM
DELAY LINE
SPACECRAFT
DETECTOR
SPACECRAFT
HOW TO DETECT BLACK HOLES
1. Mass of “compact “
companion in close
binary system (stellar
remnants only)
X-ray binary (artist’s
impression)
HOW TO DETECT BLACK HOLES
M87 disk
2. Orbital motion of
stars or gas clouds
(supermassive holes)
HOW TO DETECT BLACK HOLES
3. Random motions of
stars in galaxy’s
nucleus
(supermassive holes)
Globular cluster M3 (similar
appearance to a galactic
nucleus)
Gas almost never falls directly into a black hole
Too much “swirl”
(angular momentum) …
Gas almost never falls directly into a black hole
…makes it more
like a whirlpool
Too much “swirl”
(angular momentum) …
ACCRETION
DISK
• Like a flattened whirlpool
• Gas must give up angular
momentum to go down the drain
VISCOSITY (~FRICTION)
ACCRETION DISKS ALLOW US to
PROBE the HORIZON
Energy flows from one form to another...
GRAVITY
matter swirling inward
MOTION
friction
HEAT
RADIATION (X-rays, UV…)
ENERGY FLOW IN ACCRETION DISK
Energy flows from one form to another...
GRAVITATIONAL POTENTIAL ENERGY
falling matter
KINETIC ENERGY
compression/turbulence
HEAT
particle collisions, etc.
RADIATION
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
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
BINARY MASS FUNCTION
depends on...
• Orbit period: easy
• Doppler shift of
normal star: easy
• Mass of normal star:
hard
• Orbit inclination: hard
0.1
1
10
Log Mass (solar units)
100
NEUTRON STAR VS. BLACK HOLE:
…how to tell
• BH if:
– mass  3M Sun (reliable)
– distinctive spectrum (unreliable ????)
• NS if:
– pulsing (X-ray pulsar)
– evidence of nuclear explosions on surface
(X-ray burster)
X-ray pulsar
(accretion)
X-ray burster
(thermonuclear)