11 Black Holes and General Relativity Stuff that warps your mind.
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Transcript of 11 Black Holes and General Relativity Stuff that warps your mind.
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Black Holes Black Holes and General and General
RelativityRelativity
Stuff that warps your mind
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GoalsGoals
• Use the Scientific Method:• What proof is there of black holes?• What proof is there that black holes are
black?• Why should light be affected by
gravity?• What proof is there that it is?
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Black Holes
• Mass so great that the velocity needed to escape is greater than c.
• Need lots of mass in a small volume.
SunEH M
Mkm3R
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Seeing Black Holes
• Rips apart and heats up anything it swallows.
• Very hot thermal emission peak in X-rays.
• So what do you look for:– Massive– Small– Dark in visible– Bright in X-rays
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Cygnus X-1• 1970s• Intense source of X-
rays.• “Near” star
HDE226868.
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HDE226868
• Doppler shifts of HDE226868
• Like before, we get mass of star and unseen companion.
Mass Total
)(Separation)(Period
32 AU
yrs
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The Companion• Result:
Period = 5.6 daysTotal Mass ~ 28 x Msun
• From spectral type of HDE226868 we estimate its mass ~18 Msun.
• Companion M = 10 Msun!• Massive!• But where is its light?• Dark!• Can’t be a normal star, or even
neutron star.
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X-ray Source?
• Star brightness fluctuates every 5.6 days.
• X-rays drop off every 5.6 days!• Companion must be source of X-rays!
• REH = 30 km!
SunEH M
Mkm3R
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Supermassive Black Holes
• Photograph the center of a galaxy.
• Make spectrum of light from center.
Velocity
Dis
tan
ce
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Heart of Darkness
• From Doppler shift get a velocity.
• From picture get a separation.
• From Kepler’s Laws get a Total Mass.
Mass Total
)(Separation)(Period
32 AU
yrs
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The Dark Truth• Observe:
V = 400 km/s within 26 LY of center.• So:
– Period = 121,600 yrs– Separation = 26 LY = 1,600,000 AU
• Total Mass in central pixel:300,000,000 x Mass of Sun!
• But where’s all the light?• Small, massive, dark black hole?
• REH = 6.5 AU!
Mass Total
)(Separation)(Period
32 AU
yrs
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Are Black Holes Black?
• Why should light be affected by gravity?Newton - “Whenever you have mass you have
gravity.”
• But light has no mass!• Einstein’s General Theory of Relativity
(1915):– New way of looking at gravity.– Allows gravitational effects on light.
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General Relativity2 Main Postulates:1. The speed of light is always c.
Thou shalt not add your speed to the speed of light!
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General Relativity
2. Accelerating reference frames are indistinguishable from a gravitational force.
The Star Tours ride at Disneyland is awesome!
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Gravity Bends Light
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Is there Proof?
Scientific Method:1. Hypothesis: predict gravity bends
light.2. Test: The Sun has a lot of gravity and
should deflect star light.
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Solar Eclipse of 1919
• Hard to see stars near the Sun.
• Can see stars near the Sun during an eclipse.
• Can predict time and position of Sun during eclipse years in advance.
• Measure the positions of stars 6 months before when they are up at night.
• During eclipse, measure their positions again.
SOHO spacecraft
Result: Theory of Relativity confirmed!
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Gravitational Lensing
• If geometry right: gravity cause multiple images.
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Einstein Lenses
Copyright – J. Rhoads, WIYN
Copyright – Charles R Evans (UNC)
Einstein Ring
Copyright – L. J. King (U. Manchester)
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1111Copyright – A. Fruchter (STScI)
Abell 2218
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Space is Curved• Einstein said to picture gravity as a warp in
space. – Sagan : A “pucker” in fabric of space.
• Kepler’s Laws can all be explained by movement around “puckers.”
• Everything moving is affected, regardless of mass.
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c
distancetime
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Gravity makes time slow
S
F
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