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ASTR 1040 – October 26

ASTR 1040 – October 26. Homework 4 due today Lecture in Planetarium next Tuesday (Halloween) Second mid-term exam Thursday November 2. Website http://casa.colorado.edu/~wcash/APS1040/APS1040.html. Black Holes. Are there any Black Holes?. YES. Just 20 years ago, the answer was “probably”.

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ASTR 1040 – October 26

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  1. ASTR 1040 – October 26 Homework 4 due today Lecture in Planetarium next Tuesday (Halloween) Second mid-term exam Thursday November 2 . Website http://casa.colorado.edu/~wcash/APS1040/APS1040.html

  2. Black Holes • Are there any Black Holes? YES. Just 20 years ago, the answer was “probably”. The term didn’t exist until 1969

  3. What Happens when a neutron star exceeds its Chandrasekhar Limit? • Must Collapse • No known force powerful enough to halt the collapse • Result: Black Hole

  4. Things that don’t happen • Collapse to Singularity • Winks out of universe • Explodes by some new force • Einstein’s prediction wasn’t a “sure thing”

  5. Formation Neutron Star Collapses Now it’s inside event horizon and can never be seen again.

  6. A Newtonian Black Hole Kinetic Energy Energy Falling To Surface OR if v=c

  7. Schwarzschild Radius Two errors cancel. This is the radius of the “Event Horizon” The event horizon is a true singularity in space-time. It is a place where time and space cease to exist.

  8. Geometry of Black Hole Can you boost the signal? No, that doesn’t help. Space Curves in on itself There’s no path out!

  9. Curved Space

  10. Rubber Sheet Analogy

  11. Properties - Size The radius of a black hole is 3km per solar mass There is no limit on size or mass. Note: Volume rises as the cube of the mass. Implies the larger the black hole gets, the lower is its density. A sphere of water the size of Saturn’s orbit would be a black hole!

  12. Properties – Escape Velocity No way. Not even light can escape. No signal can escape No particle Nothing

  13. Properties – Orbital Period Material orbiting a black hole will have milli-second periods

  14. Properties - Basic • Mass (Schwarzschild Black Hole) • Electric Charge (doesn’t happen) • Angular Momentum (Kerr Black Hole) No “Surface” Features No Magnetic Fields No Pulsing “No Hair”

  15. Jump on In You won’t make it, but it would be quite a ride!

  16. Properties – Energy Emitted • Energy Released from accretion • about 0.1mc2

  17. Time Dilation Now it gets weird! Time does not run at the same rate everywhere in the universe. Twins are not always the same age. Clocks run a little bit faster in Colorado than in Washington DC. Folks in DC are actually a little slower than us. About one part in a trillion. That’s a millisecond over a lifetime.

  18. Time Dilation Some event takes dt∞ out in free space. Same event takes place at radius r from center of a black hole. Now view it from free space. Takes dt instead. Longer. It looks like things are moving slower. If you are near the black hole, the rest of the universe appears to be moving faster.

  19. Time Dilation As r approaches Rsdt gets longer and longer. When r reaches the event horizon, time stops. We know how to make a time machine with a forward switch only! Just fly to a black hole and orbit above the surface. But you can fall in really fast as viewed from outside.

  20. A “frozen star” If time stops above the surface, it can’t go in. How does the hole form? Is the material still stuck in temporal limbo just above the surface? What’s inside? If nothing can get out, then how can gravity?

  21. Hawking Radiation The vacuum makes pairs of electrons and positrons that pop into existence and then annihilate without any net effect. Above a black hole, one can get sucked in. The other annihilates above the surface to cause radiation. Since its close to the surface, the light gets redshifted escaping, but it carries energy with it!

  22. Temperature Hawking derived that the temperature of a black hole is thermal. Energy for the radiation comes from the mass of the hole. The black hole shrinks with time. That’s a really long time unless the black hole is tiny. A 1kg black hole would last only 10-16s.

  23. Artist’s impression of Cyg X-1 (NASA) 6M0 BH orbiting an O9 star. 2000pc away in Cygnus

  24. Active Galactic Nuclei Some Galaxies have Giant Black Holes in the middle,spewing relativistic jets into intergalactic space

  25. At the Center of the Milky Way8000pc away

  26. Gravity Warps Space-Time

  27. Ripples in Space Timeas Masses Spiral Inward

  28. https://youtu.be/I_88S8DWbcU https://youtu.be/y0orOwQgcCM

  29. LIGO Observatorieslaser interferometer gravity-wave observatory Hanford WA Livingston, LA

  30. Super Sensitive Equipment

  31. Detection – 2016Guaranteed Nobel Prize

  32. Gravitational Wave Event (Aug 17, 2017) TwoNeutronStars inBinarySystem

  33. NS-NS binary in- spiral and merger Gamma Ray Burst (GRB) delayed 1.7 sec “Chirp”signal

  34. LocalizationofGW170817(2017Aug17) Fermi-Integral Timing LIGO/Virgo Gamma-Ray Burst Optical Transient (inNGC4993,z=0.00980andD=40.4±3.4Mpc)

  35. NGC4993(“nearbygalaxy”) ~130millionlightyears ⬇ NOAO(NationalOpticalAstronomyObservatories)

  36. LightCurvesofGW/GRBAfterglow 2.5 2.0 0819 0820 1.5 x :::::i u. 0821 0822 1.0 0823 0824 0825 0.5 0826 0827 o.o 5000 1000015000 20000 25000 Wavelength (A)

  37. Comparison of GW/GRB Afterglow with spectra of SN Ia and SN II TypeIa TypeII X-ShooteronVLT

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