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HOW TO DETECT A BLACK HOLE

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

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HOW TO DETECT A BLACK HOLE

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  1. 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

  2. CAN WE IMAGE BLACK HOLES?

  3. 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

  4. 200 M CONSTELLATION BORESIGHT Hub Spacecraft 10 KM COLLECTOR SPACECRAFT (32 PLACES EVENLY SPACED) CONVERGER SPACECRAFT 5000 DELAY LINE KM SPACECRAFT DETECTOR SPACECRAFT MAXIM = Micro- arcsecond X-ray Imaging Mission

  5. HOW TO DETECT BLACK HOLES 1. Mass of “compact “ companion in close binary system (stellar remnants only) X-ray binary (artist’s impression)

  6. HOW TO DETECT BLACK HOLES M87 disk 2. Orbital motion of stars or gas clouds (supermassive holes)

  7. 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)

  8. Gas almost never falls directly into a black hole Too much “swirl” (angular momentum) …

  9. Gas almost never falls directly into a black hole Too much “swirl” (angular momentum) … …makes it more like a whirlpool

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

  11. 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

  12. 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.

  13. 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

  14. ALGOLSCAN 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

  15. BINARY MASS FUNCTIONdepends on... • Orbit period: easy • Doppler shift of normal star: easy • Mass of normal star: hard • Orbit inclination: hard 10 100 0.1 1 Log Mass (solar units)

  16. 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)

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

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