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Black Holes & Relativity

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  1. Black Holes & Relativity

  2. In this chapter you will discover… • Einstein’s theory of general relativity • space and time are not separate entities • how black holes arise • surprisingly ‘simple’ theoretical properties of black holes • X rays and jets of gas are created near many black holes

  3. Relativity • Einstein’s vision • Theorized Time & Distance cannot be measured absolutely • Time & Distance only have meaning when measured relative to something

  4. The “Up” Paradox • In childhood, we regard “up” as a single direction above our head. • When we realize that people in Australia do not stand upside-down… • we revise our common sense • “up” is defined relative to the center of the Earth

  5. What is Relative? • A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • What an observer sees depends on her/his position!

  6. What is Relative? • A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • An observer on the Earth’s surface? => Would see the plane fly westward overhead

  7. What is Relative? • A plane flies WEST from Nairobi to Quito at 1,000 mi/hr. • The Earth rotates EAST at the equator at 1,000 mi/hr. • An observer far away in space? => Would see the plane not seem to move at all, and the Earth turn under it!

  8. Motion & Reference • Objects moving relative to one other are in different reference frames. • They experience time and measure distance & mass in different ways

  9. Einstein’s Vision • 1905: Special Relativity • Speed of Light is the same for ALL observers • No matter how fast they are moving! • No matter what direction they are moving!

  10. Special Relativity Consequence • Length is different for moving observers • Stationary observers measure longer lengths • Moving objects appear to be shorter • Time is different for moving observers • Stationary observers measure longer times • Time for Moving objects appears to be less • Energy and Mass are related (E = mc2)

  11. A ball in moving train… Seen from INSIDE the train, the ball simply goes UP and DOWN in a certain time tinside observer

  12. A ball in moving train… Seen from OUTSIDE the train, the ball goes UP and DOWN, but ALSO sideways at the speed of the train, say in a certain time toutside observer

  13. A ball in moving train… The faster the train is moving, the faster the ball appears to be going to an outside observer

  14. A ball in moving train… The faster the train is moving, the faster the ball appears to be going to an outside observer, covering a longer distance in that same time toutside observer

  15. So what?? • Replace the Ball with a Beam of Light And… • Suppose both inside and outside observers assume the speed of light is the same

  16. A light beam in moving train… For the observer in the train, the light moves up and down at the speed of light, in a time tinside observer

  17. A light beam in moving train… For the observer OUTSIDE the train, the light travels farther ….

  18. A light beam in moving train… For the observer OUTSIDE the train, the light travels farther …. – but if it moves at the same speed of light – it must take longer! toutside > tinside

  19. Consequences! Time measured by someone moving is different than time measured by someone who isn’t! toutside observer > tinside observer

  20. Consequences! Time measured by someone moving is different than time measured by someone who isn’t! toutside observer > tinside observer The faster you go, the greater the difference in your perception of time vs. for someone not moving!

  21. Proof! • Decay of Subatomic Particles (Muons) (cf. http://www.scivee.tv/node/2415 ) • Actual Aircraft Travel (Hafele-Keating exp.) (cf. http://www.youtube.com/watch?v=gdRmCqylsME) • GPS satellites! (cf. https://www.youtube.com/watch?v=30KfPtHec4s(cf. https://www.youtube.com/watch?v=zQdIjwoi-u4 ) • Nuclear Colliders

  22. Additional Consequences of Special Relativity • Time as measured by stationary observer is longer • Length as measured by stationary observer is longer • Mass as measured by stationary observer is more • All compared with measurements made by moving observers…

  23. Additional Consequences of Special Relativity • Time is relative! (http://www.scivee.tv/node/3025) • Time Dilation (cf. http://www.scivee.tv/node/3007) • Length as measured by stationary observer is longer • Mass as measured by stationary observer is more • All compared with measurements made by moving observers…

  24. Traveling to the Stars

  25. The Doppler Shift Explained through Relativity Speed of light is measured to be identical but… observed frequency (wavelength) is not!

  26. Einstein’s Vision • 1915: General Relativity • Acceleration “upward” is equivalent to gravitation “downward” • You can’t tell the difference • Matter will bend space and time

  27. Time is affected by gravity

  28. Light is affected by gravity • According to Einstein’s Theory of Relativity, gravity is really the warping of spacetime about an object with mass. • This means that even light is affected by gravity.

  29. Proof! • Deflection of Starlight by the Sun • 1919 Total Solar Eclipse • Precession of Mercury’s orbit • Gravitational Redshift of light moving up • Delay in signals from Spacecraft on Mars

  30. Radio Signals from Mars Mars Orbiters & Landers send signals to Earth Signals travel at speed of light across solar system

  31. Radio Signals from Mars Signals bent by gravitation of the Sun Signals take longer to reach us than predicted

  32. So what happens to light near a VERY massive object?

  33. Black Holes& General Relativity

  34. Black Holes – Theory! • After a massive star supernova, if core mass > 3 M, force of gravity will be too strong for even neutron degeneracy to stabilize star. • The star will collapse into a singularity. • This is what we call a black hole.

  35. Black Holes - Theory • The star becomes infinitely small. • it creates a “hole” in the Universe • Since 3 M or more are compressed into an infinitely small space, the force of gravity NEAR to the star is HUGE!!! • WARNING!! • Newton’s Law of Gravity is no longer valid !!

  36. Black Holes - Theory • Defined by their event horizon • Radius inside of which light cannot escape (Schwarzschild radius)

  37. Black Holes - Theory • Defined by their rotation • Rapidly rotating holes will affect space around them

  38. Rotating Black Holes “drag” space around them

  39. Black Holes - Theory • Defined by their event horizon • Radius inside of which light cannot escape (Schwarzschild radius) • Defined by their rotation • Rapidly rotating holes will affect space around them • But how can they be observed??

  40. Black Holes affect Time in nearby space

  41. Black Holes affect matter in nearby space, too

  42. Cygnus X-1 • A candidate for a *stellar-sized* black hole • ~ 11x more massive than Sun. • 8000 ly away.

  43. Black Holes can emit “jets” of radiation