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Trip to a Black Hole I

Extraordinary Concepts in Physics. Lecture 4. Trip to a Black Hole I. by  Robert J. Nemiroff  Michigan Tech. Physics X: About This Course. Officially "Extraordinary Concepts in Physics" Being taught for credit at Michigan Tech Light on math, heavy on concepts Anyone anywhere is welcome

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Trip to a Black Hole I

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  1. Extraordinary Concepts in Physics Lecture 4 Trip to a Black Hole I by  Robert J. Nemiroff  Michigan Tech

  2. Physics X: About This Course • Officially "Extraordinary Concepts in Physics" • Being taught for credit at Michigan Tech • Light on math, heavy on concepts • Anyone anywhere is welcome • No textbook required • Wikipedia, web links, and lectures only • Find all the lectures with Google at: • "Starship Asterisk" then "Physics X"  • http://bb.nightskylive.net/asterisk/viewforum.php?f=39

  3. Trip to a Black Hole: Overview • Schwarzschild black hole only • It's the easiest • It's what I know best • Based partly on my paper: •  "Visual distortions near a neutron star and black hole" • American Journal of Physics 1993, 61, 619 • And my web page:   • Virtual Trips to Black Holes and Neutron Stars

  4. Trip to a Black Hole: Key Distances • r = infinity: space is flat: aN = GM/r2 • Near the black hole: a = aN / (1 - rs/r)1/2 • r = 3 rs: last stable orbit • r = 1.5 rs: photon sphere • r = rs: event horizon • r = rc: Compton radius • r = 0: GR singularity

  5. Trip to a Black Hole: Far Away • r -> infinity: space is "flat" • all (1 - rs/r) terms go to 1. • gravity is Newtonian:  aN = GM/r2 •  black holes attract the same as normal matter • curved universe NOT flat as r -> infinity • can see lensing effects with a telescope  • orbiting the same as spinning in place

  6. Trip to a Black Hole: Approaching • black hole appears black • excludes evaporation effects • blackness everywhere inside photon sphere • cannot see to the event horizon • outside, average surface brightness unchanged • appears fuzzy as star images merge • distant universe  • speeds up • appears bluer

  7. Background: Gravitational Lensing • gravity bends light: "null geodesics"

  8. Gravitational Lensing:Einstein Ring • Actual Einstein ring: APOD 2008 July 28

  9. Gravitational Lensing:Einstein Ring • Detailed image of Einstein ring from AJP paper

  10. Trip to a Black Hole: Orbiting Nearby

  11. Trip to a Black Hole: Orbiting at 10 rs  • Stars CANNOT cross the Einstein ring • Einstein ring mapped point behind BH center • Einstein ring divides complete image sets • Angular speeds diverge at the Einstein ring • One can see oneself  • All stars have two discernible images • One outside the ER, one inside • Observers also have two images • Actually, an infinite number of images exist

  12. Trip to a Black Hole: Orbiting at 10 rs  • Distant stars appear slightly bluer • Distant clocks appear to run faster • This also occurs for stars that appear next to the black hole • Objects ACTUALLY nearer to the black hole • Appear redder • Clocks appear to run slower

  13. Trip to a Black Hole: Orbiting at the Photon Sphere

  14. Trip to a Black Hole: Orbiting at the Photon Sphere • Everything below you is black • because those light paths fall into the BH • The whole sky appear above you • because those light paths escape the BH • The Einstein ring appears above the horizon • Stars still CANNOT cross the Einstein ring • Stars still speed up near the Einstein ring

  15. Trip to a Black Hole: Orbiting at the Photon Sphere • Other image sets between other Einstein rings • "The" Einstein ring actually "First Sky Einstein ring" • There are infinitely many Sky Einstein rings • Every radius from the BH has  • its own infinite set of Einstein rings • its own redshift (or blueshift)

  16. Gravitational Lensing:Einstein Ring • Einstein rings near a black hole

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