Big Bang, Black
Holes, No Math
ASTR/PHYS 109
Dr. David Toback
Lecture 24
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
1
Was Due Today– L24
• Reading:
– (Unit 5)
• Pre-Lecture Reading Questions:
– Unit 5 Revision (if desired): Stage 2
• End-of-Chapter Quizzes:
– Chapter 16
• Papers:
– Paper 3 Revision (if desired):
• Stage 2 due Monday
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
2
Unit 5: Big Objects
1.Galaxies
2.Star Birth and
Death
3.More on Black
Holes
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
Today
3
Where are we now in the history?
Half a billion years after the bang
Black holes start forming
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
4
Paper 4: The Assignment
• Abbreviated Description: What is the evidence
for Stellar Black Holes? Note there is an
emphasis on what is a black hole and how it
forms.
– Explain it to someone who isn’t taking the
class (no jargon)
• Make sure you read ALL the instructions
• Same format and due dates as usual
– Text due 1 week after we finish Chapter 17
– Calibration, reviews and self-assessment due
a week after
that
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
5
Outline
• What makes Black Holes black
• What a black hole would look
like to a nearby observer
• Evidence for Black Holes
• Different types of Black Holes
• A few words on why black holes
are so important in cosmology
and our understanding of the
Big Objects and Black Holes
Big Bang,
Black
6
Big
Bang
Topic 3: Properties of Black Holes
Holes, No Math
Moving Towards Black Holes
• If a neutron star has a “critical
mass” (about 3MSun) it can
continue to collapse
• Nothing strong enough to oppose
the crush of gravity! 
Continues to collapse until it
becomes a single point in space
• Call this a Black Hole
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Why do we call it a black hole?
Call it a Black
Hole because light
can’t “escape”
Say more about
what this means
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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What they are… and aren’t
• Black holes aren’t demonic, sucking
power holes
• A black hole is just another thing a star
can turn into when it runs out of fuel
• It is basically a really massive ex-star
• Then again, something with that much
mass but a size smaller than a proton
does have some unusual properties
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
9
The Sun in Space
• What if the Sun
compressed into a
Neutron Star?
• Shrink Sun to
10% of its size
• Now 1%
• Neutron star is
0.004% of its
size
• What if it were
crushed into a
1.4 Million Kilometers across
blackBlack
hole? Big Objects and~25
Black
Holes
Big Bang,
Kilometers
across 10
Holes, No Math
Topic 3: Properties of Black Holes
The Curvature of Space-Time
near the Sun
The size of the Sun…
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
11
How the Curvature Changes as
we Compressing the Sun
Far outside
What if we
the Sun you
compressed the Sun can’t really
into a Neutron Star? tell the
difference
You can tell
the difference
if you are
very close to
the Sun itself
The sun is now a few kilometers across
Big Objects and Black Holes
Big Bang, Black
Topic 3: Properties of Black Holes
Holes, No Math
12
Compress the Sun into a Black Hole
Infinite curvature
Big Bang, Black
Holes, No Math
• Black hole is just
a point in space
• Here we looking at
the CURVATURE
of Space-time
• Far outside the
Sun the curvature
isn’t very
different, but
very close to the
center is very
different
Big Objects and Black Holes
Topic 3: Properties of Black Holes
13
What does this
have to do with
light being able to
escape?
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
14
Small speed objects can’t leave the Earth
How fast does it need to move so that it
can “escape” the pull of gravity? Call this
the escape velocity
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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The Moon has a “small” escape Velocity
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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The Escape Velocity for the Earth
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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The Sun
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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A Neutron Star
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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A Black Hole
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Why do we call it a Black Hole?
A Black Hole is so dense that
it’s escape velocity is
GREATER than the speed of
light  light can no longer
escape!
Looks at this from the
perspective of the curvature
of Space-Time
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
21
Space-Time as an Escalator
Can think of space
near a star as an
escalator moving
downward
towards the
surface of the
star
A person in curved
space-time
moves downward
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
22
Later time
Even though
he is walking
in the “up”
direction, his
overall
motion is
actually
downwards
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
23
Even later times.
If the man moves
slower than the
speed of the
escalator he will
move backwards
If the escalator is
moving down faster
than the speed of
light, even light
can’t go “up”
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Space-Time Near a Black Hole
• The gravity of a Black
Hole curves space-time
SO MUCH that light
simply can’t leave
• If light can’t escape
then we can’t “see” light
from it and our star
“appears” black
• Since light could fall in,
and never come back
out, we call it a “Black
Hole”
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Black Holes
Light falls in and never comes back
Light from inside can’t escape!
Path of light passing nearby gets bent
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Weird…
What if our Sun were to
(magically??) turn into a Black
Hole?
The gravitational attraction far
outside wouldn’t change, so the
planets would continue to orbit
Then again, without the light it
would get really cold and we’d
all die… Big Objects and Black Holes
Big Bang, Black
27
Holes, No Math
Topic 3: Properties of Black Holes
Different Types of Black Holes
• Two different types
1. Stellar Black Holes (the types we have
been discussing)
2. Supermassive Black Holes
• Both have been observed and are now known
to be common
– Closest known stellar Black Hole is about
3,000 light years away
• Supermassive Black hole at the center of the
Milky Way with a mass more than one million
times that of our sun
– At the center
of
many
(all?)
large
galaxies
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
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Some pictures from Chapter 2
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Supermassive Black Holes
• Still learning about how they came to be. Some people
think they started as a stellar Black Hole near the
center of the galaxy when the galaxy was forming a
half a billion years after the bang
– “Ate” material that fell towards the center of the
galaxy
– Lots of light came from the atomic interactions as
the material fell in
– Called a Quasar
• Today: nothing falling in since everything either
already fell in or is now rotating around the center of
the galaxy
– Quasars onlyBigobserved
in “distant” galaxies
Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
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Switch Topcs
• Life near a black
hole
• Evidence for
black holes
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
31
Getting a Close-Up Look
What would a
Black Hole
look like to an
observer who
tries to get a
closer look?
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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An Astronaut Near a Black Hole
Light falls in and never comes back
The same thing is true for our Astronaut
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Event Horizon
• A rocket with a speed of 11km/sec can
escape from the Earth
– Needs a lower speed if it starts up
high in the atmosphere
– The higher it is, the smaller the
escape velocity is
• We call that special distance from the
center of a black hole where the escape
velocity is equal to the speed of light
the EVENTBigHORIZON
Objects and Black Holes
Big Bang, Black
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Holes, No Math
Topic 3: Properties of Black Holes
Spaghettification as he falls in…
• The gravitational
pull on his feet
would be much
stronger than on
his head
• He’d get
stretched out and
then ripped apart
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
35
Falling into a Black Hole
Spaghettification as he falls in
Can’t see him after he passes the event horizon…
not even Big
light
from
can escape 36
Objects
and his
Blackgun
Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
A way to observe Stellar Black
Holes?
• Let’s say we have
two stars orbiting
each other (a
binary pair), and
one has already
turned into a
black hole
• We can “see” light
“from” a Black
Hole by watching
them “eat” their
Big Objects and Black Holes
Big Bang, Black
companion
Topic 3: Properties of Black Holes
Holes, No Math
37
Black Holes Suck
• Can think of the stuff
sucked in like crumbs
on the surface of the
water as it goes down
the sink  swirl faster
and faster until it
reaches the drain and
gets sucked down
• As the matter moves
more quickly the atoms
collide
• These collisions
produce light that we
can see  x-rays
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
38
A way to observe Supermassive
Black Holes
• Can observe supermassive black holes by looking
at stars as they orbit “nothing” at the center of
a galaxy
• Can even measure their mass like the way we
measure the mass of the Sun
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Measuring the Mass of a Stellar
Black Hole
Can also measure
the mass of a
stellar black
hole if its in a
binary pair by
watching the
speed of its
“partner” orbit
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
40
Last Topic on Black Holes…
Why are Black
Holes
important in
Cosmology?
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
41
Theory
In the 1970’s Hawking and
Penrose realized that the
creation of a Black Hole looks
like a Big Bang in reverse
Said differently, the Big Bang
appears to be the creation of a
Black Hole running backward in
time…
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Theory?
• Inside a Black Hole we get “infinite
curvature” and “infinite density” of
space
– A singularity
• Here the particles would interact
according to Quantum Mechanics
• Hard to calculate things… Quantum
Mechanics and General Relativity
predict different things and we
don’t know which one is right…
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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In a way, this is Good…
• Since we now have observed
Black Holes, we finally have a
set of objects we can look at
• Maybe by studying their
properties we can tell which
theory (if either) is correct
• Maybe neither? Maybe
something like Quantum Gravity?
String Theory?
… Stay tuned… 44
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
Paper 4: The Assignment
• Abbreviated Description: What is the evidence
for Stellar Black Holes? Note there is an
emphasis on what is a black hole and how it
forms.
– Explain it to someone who isn’t taking the
class (no jargon)
• Make sure you read ALL the instructions
• Same format and due dates as usual
– Text due 1 week after we finish Chapter 17
– Calibration, reviews and self-assessment due
a week after
that
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
45
For Next Time – L24
No class Wednesday, but
everything is still due as scheduled
• Reading:
– Unit 6
• Pre-Lecture Reading Questions:
– Unit 6: Stage 1
• End-of-Chapter Quizzes:
– Chapter 17 if we finished Chapter 17 (else just Chapter
16)
• Papers:
– Paper 3 Revision (if desired):
• Stage 1 due Monday before class
– Paper 4:
• Due 1 week from today if we finished Chapter 17
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Clicker Question
Can you "fill up" a black
hole?
a) Yes
b) No
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Clicker Question
Can a Black Hole orbit another
star?
a) Yes
b) No
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Clicker Question
Could the Earth orbit a
black hole?
a)Yes
b)No
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Clicker Question
What would happen if two black
holes collided?
a)They would make a supermassive
black hole
b)They would just make a black
hole that is the mass of the two
black holes that started
c) Black holes can’t collide
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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1 Paragraph in-class Quiz
What is the evidence for
stellar black holes?
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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For Next Time – L23
• Reading:
– Unit 6
• Pre-Lecture Reading Questions:
– Unit 6: Due Monday before class
• End-of-Chapter Quizzes:
– Chapter 17 if we finished Chapter 17 (else just
Chapter 16)
• Papers:
– Paper 3 Revision (if desired):
• Stage 2 due Wednesday before class
– Paper 4:
• Due 1 week from today if we finished Chapter
17
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
53
For Next Time – L24
• Reading:
– Unit 6 (was due already)
• Pre-Lecture Reading Questions:
– Unit 6: Stage 2 due Wednesday before class
• End-of-Chapter Quizzes:
– Chapter 17
• Papers:
– Paper 3 Revision (if desired):
• Stage 2 due Wednesday before class
– Paper 4:
• Stage 1 eue 1 week from today (Monday)
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Was Due for Today– L25
• Reading:
– Chapter 18
• Pre-Lecture Reading Questions:
– Chapter 18
• End-of-Chapter Quizzes:
– Chapter 16 (also check 14)
• Papers:
– Paper 3: Done fixing broken rubrics. Now
working on recent re-grade requests.
– Paper 3 Revision: Now open for submission.
Text due Monday before class
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Was Due for Today– L26
• Reading:
– Chapter 20
• Pre-Lecture Reading Questions:
– Chapter 20
• End-of-Chapter Quizzes:
– Chapter 16 (also check 14)
• Papers:
– Paper 3: Working on recent re-grade
requests.
– Paper 3 Revision: Now open for submission.
Text due Monday before class
– Paper 4: Now open for submission. Text
Bigbefore
Objects and
Black Holes
Big Bang,
Black
56
due
Monday
class
Holes, No Math
Topic 3: Properties of Black Holes
Prep for Next time – L25
• Reading:
– Chapter 19 and 20
• Pre-Lecture Reading Questions:
– Chapter 19 and 20
• End-of-Chapter Quizzes:
– If we finished Chapter 17 then end-of-chapter
quiz 17 (else just through Chapter 16)
• Papers:
– Paper 3: Done fixing broken rubrics. Now working
on recent re-grade requests.
– Paper 3 Revision: Now open for submission. Text
due Monday before class
– Paper 4: Due one week from today
Big Bang, Black
Holes, No Math
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Topic 3: Properties of Black Holes
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Was due today – L12
• Reading:
–BBBHNM: All reading through Chapter 19
•Reading Questions:
– All reading questions through 19
• eLearning Quizzes:
– Chapter 17
• Papers:
– Rest of Paper 3 assignment (if you
resubmitted a revision) due before class
today
– Text of Paper 4 due Wednesday night at
11:55PM Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
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End of the Semester – L12
• Only 3 more days of class
– Today, April 22nd, and April 29th
• Need to finish all the end of Chapter
quizzes as well as AMS 2
– That’s my of semester evaluation
(there will be another)
– Need to finish this before you can
finish all the end of chapter quizzes
• Will not do the 5th paper, but will allow
Early Times & Fate of the Universe Topic 1:
Big Objects
and Black Holes
Big Bang,
Black 4 revision
Possibilities
a paper
59
Holes, No Math
Topic 3: Properties of Black Holes
Prep For Next Time – L11
• Reading:
–BBBHNM: All reading through Chapter 19
• Reading Questions:
–All reading questions through 19
• eLearning Quizzes:
– Through Chapter 17
• Papers:
– Rest of Paper 3 assignment (if you resubmitted a
revision) due before class on Monday
– Paper 4 will due Wednesday at 11:55PM and the
Calibrations/Reviews/Self-Assessment will be due
Monday before class.
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Prep For Next Time – L11
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 19
• Reading Questions:
–All reading questions through 19
• eLearning Quizzes:
– If we finished Chapter 16 then end-of-chapter
quiz 16 (else just through Chapter 15)
• Papers:
– Rest of Paper 3 assignment (if you resubmitted a
revision) due before class on Tuesday
– Since we did not finish Chapter 17, Paper 4 will
be assigned Tuesday
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Prep for Today (Is now due) – L23
• Reading:
– BBBHNM 18
• Reading questions:
– Chapter 18
• End-of-Chapter Quizzes:
– Chapter 16
• Paper Stuff
– Paper 3: Misgraded? Let us know
• Revision due Monday before class. Want
feedback? Due Thursday
– Paper 4: Will be due 1 week after we
finish Chapter
17
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
62
Prep for Today (Is now due) – L23
• Reading:
– BBBHNM 18
• Reading questions:
– Chapter 18
• End-of-Chapter Quizzes:
– Chapter 16
• Paper Stuff
– Paper 3: Misgraded? Let us know
• Revision due Monday before class. Want
feedback? Due Thursday
– Paper 4: Will be due 1 week after we
finish Chapter
17
Big Objects and Black Holes
Big Bang, Black
Holes, No Math
Topic 3: Properties of Black Holes
63
Prep for Today (Is now due) – L24
• Reading:
– Rest of BBBHNM
• Reading questions:
– Some of the rest of the chapter, finish all by the
end of the semester
• End-of-Chapter Quizzes:
– Chapter 16
• Paper Stuff
– Paper 3: Misgraded? Let us know
– Paper 3 Revision: Due Monday before class. Want
feedback? Due Thursday
– Paper 4: Will be due 1 week after we finish
Chapter 17
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
64
Prep For Next Time – L12
• Note: May change depending on how far we get in
lecture
• Reading:
–BBBHNM: All reading through Chapter 20
• Reading Questions:
– All reading questions through 20
• eLearning Quizzes:
– If we finished Chapter 17 then end-of-chapter
quiz 17 (else just through Chapter 16)
• Papers:
– Text of Paper 4 assignment due before class on
Tuesday
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Prep for Next Time – P23
• Reading
– Reading the rest of BBBHNM
• Reading questions
– Chapter 18, 19 and 22 (can do in installments)
• End-of-Chapter Quizzes
– If we finished Chapter 17 then end-of-chapter
quiz 17 (else just 16)
• Papers
– Paper 2 Revision or Paper 3: Misgraded? Let us
know.
– Paper 3 Revision: Due Monday before class.
Want feedback? Due Friday for quick response
– Paper 4: Final date assigned when we finish
17 Big Objects and Black Holes
Big Bang,Chapter
Black
Holes, No Math
Topic 3: Properties of Black Holes
66
Full set of Readings So Far
• Required:
– BBBHNM: Chaps. 1-18
• Recommended:
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11
(117-137), 12
• SHU: Chaps. 1-3, 4(77-86), 5(95-114),
6-8 (up-to-page 164)
• TOE: Chaps. 1-3
• Seeds (Cosmology in the 21st Century)
Big Bang, Black 67 Big Objects and Black Holes
Topic 3: Properties of Black Holes
Holes, No Math
More on Our Astronaut
• Suppose he sends us a signal every
second, according to his watch, as he
falls in
• As he falls into the star space-time
gets stretched more and more
– The time between signals gets
stretched also
– His signals appear to get further and
further apart in time
– His signals are red-shifted
Big Bang, Black
Holes, No Math
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Topic 3: Properties of Black Holes
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Astronaut Continued
• Any light reflecting off him
is red-shifted also, so he
looks “redder and redder”
• Eventually, his signals “fall”
into the Black Hole and we
can’t see them (or him)
anymore
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Prep for Next Time – P22
• Reading
– BBBHNM 18
• Reading questions
– Chapter 18
• End-of-Chapter Quizzes
– If we finished Chapter 17 then end-of-chapter
quiz 17 (else just 16)
• Papers
– Paper 2: Misgraded? Let us know
– Paper 3: Misgraded? Let us know
– Paper 4: Will assign paper 4 next time
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
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Announcement
before we
begin
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
71
Time near a Black Hole
The passage of
time for an
observer near or
on a Black Hole
is different than
we observe
because spacetime is different
in curved space
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
72
Evidence for Black Holes?
Hubble Space
Telescope data
Cygnus XR-1
Look at the hot
gas swirling
around “Nothing”
A “blob” breaks
off then swirls in
and disappears
like an astronaut
would
Big Objects and Black Holes
Big Bang, Black
http://oposite.stsci.edu/pubinfo/pr
/2001/03/content/CygnusXR-1.mpg
Holes, No Math
Topic 3: Properties of Black Holes
73
How do we Observe Black Holes?
• We can “see”
Black Holes
“eating” other
stars
• They are so
massive that the
gravitational
attraction can
“suck” off stuff
from another
star
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
74
Black Holes Suck
• Can think of the stuff
sucked in like crumbs
on the surface of the
water as it goes down
the sink  swirl faster
and faster until it
reaches the drain and
gets sucked down
• As the matter moves
more quickly the atoms
collide
• These collisions
produce light that we
can see
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
75
The Sun in Space-Time
The size of the Sun…
Big Bang, Black
Holes, No Math
Big Objects and Black Holes
Topic 3: Properties of Black Holes
76
Compressing the Sun
What if we
compressed the Sun
into a Neutron Star?
Far outside
the Sun you
can’t really
tell the
difference
You can tell
the difference
if you are
very close to
the Sun itself
The sun is now a few kilometers across
Big Objects and Black Holes
Big Bang, Black
Topic 3: Properties of Black Holes
Holes, No Math
77
Light in Space-Time
• Doesn’t light
just always
travel at the
speed of light?
• Yes, but it’s
path can curve
in space-time…
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The Sun in Space-Time
Anything faster than 620 km/sec
can escape
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Neutron Stars
Only things faster than half the
speed of light can escape
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Black Holes
Nothing can escape unless it is
traveling faster than the speed
of light
No matter
how fast it’s
going it can’t
leave
Space is
falling into
the hole too
Big Bang,
Black
quickly
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Papers
• Paper 1 is done
• Paper 2 grades are on eLearning
– Working on getting the revised grades fixed
• Paper 3:
– Let us know if you think you have been mis-graded
– Revisions must be submitted by Wednesday at noon
• Paper 4:
– Now open
– Due next Monday before class
• Paper 5 (last paper, no final)
– Assigned after we start Chap 20
Big 82
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Other Stuff
• Elearning:
–Unit 5 in progress
• Make sure you pick up the
latest version of the online
textbook!!!
–Been updating it all
semester
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The Reading So Far and For Unit 5
Reading for Unit 5:
• BBBHNM: Chaps. 15-17
• SHU: 4(87-93)
• TOE: 3
• BHOT: 8(76-85)
Full reading through Unit 5:
• BBBHNM: Chaps. 1-17
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-85), 9 and 11
(117-122)
• SHU: Chaps. 1-3, 4(77-93), 5(95-114), 6, 7
(up-to-page 159)
Objects and Black Holes
• Bang,
TOE:Black
Chaps. Big
1-3
Big
84
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For Next Time
Unit 6: Early Times and the Fate of the Universe
Full reading for Unit 6:
• BBBHNM: Chaps. 18-22
• SHU: 8 (159-164)
• BHOT: 11 (122-137), 12
• Seeds (Cosmology in the 21st Century, Web Handout)
Full reading through Unit 6:
• BBBHNM: Chaps. 1-22
• TFTM: Chaps. 1-5
• BHOT: Chaps. 1-7, 8 (68-76), 9 and 11 (117-137), 12
• SHU: Chaps. 1-3, 4(77-86), 5(95-114), 6-8 (up-to-page 164)
• TOE: Chaps. 1-3
• Seeds (Cosmology in the 21st Century)
Lecture prep: Turn in on eLearning
Two questions from Chapter 18 you want to know the answer to
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Overview
• The way Galaxies and Stars
form is very similar
• The way stars “die” depends
on the star itself… sometimes
they die to form a Black
Hole
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The Life and Death of Stars
Small Star
(Red Giant)
White Dwarf
Big Star
(Supergiant)
Explodes
(Supernova)
Neutron Star
Brown Dwarf
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Black Hole
Slightly more complicated than this…
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Writing Assignments
Short Assignments 1 & 2
Re-do’s are still possible.
Want to revise again? Talk to
me
eLearning:
Unit 4 now due
Need to be working on Unit 5
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Papers AFTER Paper 2
Two options
1.Two short papers like the first one
• One on Black Holes (due one week
after we finish Black Holes)
• One on Dark Matter (due last day
of class)
2.Research Paper
If you want this option Stage 1 must
be approved ASAP
• Was due last week
• Final paper due the last day of
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th
Holes
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Black
89
Tuesday
Dec
8
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Outline
• What makes Black Holes black
• What a black hole would look
like to a nearby observer
• Black Holes ain’t so black…
• A few words on why black holes
are so important in cosmology
and our understanding of the
Big Bang
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90
How do we Observe Black Holes?
• We can “see” Black
Holes “eating” other
stars
• They are so massive
that the
gravitational
attraction can
“suck” off stuff
from another star
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Black Holes
ain’t so
black…
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Quantum Mechanics
Weird: Pairs of particles can be created
but they have to disappear again quickly
because of Quantum Mechanics
e-
e+
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Need to
conserve energy
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Black Holes ain’t so Black
Even Weirder: Near a Black Hole the
pairs of particles can get split up
One gets sucked in and the other goes
off and we can see it!
e
+
e
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So What?
• By conservation of energy, one will
have positive energy and the other
will have “negative” energy
• Since the negative energy particles
fall into the black hole, by
Einstein’s E=MC2 equation, the mass
of the Black Hole goes down
• To an observer at a distance the
particle will appear to have been
“emitted” from the Black Hole
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Can a Black Hole “Evaporate”?
• We can do the calculation…
 Estimates are that it will
take 1066 years
• Compare to the age of the
Universe: 1010 years
• In other words… don’t hold your
breath…
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Can we see this?
Example of a
Black Hole
• Stuff swirling
into the middle
• A stream of
particles coming
out
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Black Holes Suck
• Can think of the stuff
sucked in like crumbs on
the surface of the
water as it goes down
the sink  swirl faster
and faster until it
reaches the drain and
gets sucked down
• As the matter moves
more quickly the atoms
collide
• These collisions produce
light that we can see
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http://science.nasa.gov/headlines/images/blackhole/blackhole-swirl.jpg
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Black Holes
Nothing can escape unless it is
traveling faster than the speed
of light
No matter
how fast it’s
going it’s
path is back
into the
Black hole
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Schedule from Here on Out
• Wed Nov 19th: 25th lecture:
– Recitation for Paper 2
• Please bring a copy of your outline and be
prepared to discuss it
• Will be checked off at the end of class as your
in-class quiz
– Inflation
• Mon Nov 24th: 26th lecture: Dark Energy
• Wed Nov 26th: No class
– Research paper and 2nd short paper due at midnight
– Day before Thanksgiving. Class cancelled
• Dec 1st: No classes redefined day
• Dec 3rd: Reading period, no classes
• Dec 8th: Finals week, no final
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What is a Black Hole?
• A Black Hole is a really REALLY
DENSE star
• REALLY curves the space time
around it…
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Escape Velocity
• The escape velocity for the
Earth is about 11.2 km/sec
• The escape velocity for the sun
is about 620 km/sec
• The escape velocity of a
neutron star is about half the
speed of light!
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Why do we call it a Black Hole?
• The escape velocity for the Sun is
about 620 km/sec
• The escape velocity of a neutron
star is about half the speed of
light!
• The escape velocity for a Black Hole
is GREATER than the speed of light!
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Paper 2
• On Wednesday we will devote the
first part of lecture for small group
discussions of your Short-Paper 2
• Please bring a copy of your outline
and be prepared to discuss it
• Will be checked off at the end of
class as your in-class quiz
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Schedule from Here on Out
• Mon Nov 17th: 24th lecture: Black Holes
• Wed Nov 19th: 25th lecture:
– Recitation for Paper 2
– Inflation
• Mon Nov 24th: 26th lecture: Dark Energy
• Wed Nov 26th: No class
– Research paper and 2nd short paper due at
midnight
– Day before Thanksgiving. Class cancelled
• Dec 1st: No classes redefined day
• Dec 3rd: Reading period, no classes
• Dec 8th: Finals week, no final
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That’s it
• It’s been a real pleasure
• Stay in touch, and best of luck
in the future!
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Remaining Assignments
• Writing Assignments Due Thursday
– However, you may turn it in, via
email, on Monday
– If you want to revise your paper
you’ll need to pick it up from me
directly
• Don’t forget to finish your WebCT
stuff
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Next Time
• Back to Section 5: Early
Times and the Fate of the
Universe
–Inflation
–Dark Energy
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• Said differently, a Big Bang
could occur provided only that
General Relativity is correct and
that the universe contains as
much matter as we observe
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• As the mass goes down the area of its
event horizon goes down…
• Might black holes eventually evaporate?
• Estimates are that it will take 1066
years
• Compare this to the 1010 years which is
the age of the universe
• In other words… don’t hold your breath…
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TOE 4 cont…
• The smaller the black hole, the
easier it is for one of the
particles to escape
• Thus the rate of emission will
be greater and the apparent
temperature of the black hole
will be higher
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TOE 4 cont…
• The smaller the black hole, the less far
the particle with negative energy will
have to go before it becomes a real
particle
• Thus the rate of emission will be
greater and the apparent temperature
of the black hole will be higher
• Since the negative energy particles fall
into the black hole, by Einstein’s E=MC2
equation, the mass of the black hole
goes down
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So What?
• By conservation of energy, one will have positive energy and the
other negative energy
• Real particles (electrons etc.) always have positive energy,
however the gravitational field inside a black hole is so strong
that even a real particle can have negative energy there
• BHOT 10…It is therefore possible for virtual particles
with negative energy to fall into a black hole and
become real particles
• Its partner may fall into the black hole also
• However, since it has positive energy it is also
possible for it to escape to infinity as a real particle
• To an observer at a distance it will appear to have
been emitted from the black hole
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TOE 4 cont…
• There can be quantum fluctuations
in empty space
• One can think of these fluctuations
as pairs of particles of light or
gravity that appear together at
some time, move apart and then
come together again and annihilate
each other
• These are known as virtual particles
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Our Astronaut
• Suppose he sends a signal every
second, according to his watch,
to us as he falls in
• He begins transmitting at 2
seconds before 11:00
• What will the spaceship record?
• TOE 3, p54
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• Do we really want to spend time on
HOW black holes are observed?
• All the quasars we see are REALLY far
away, which means we are observing
them from a LONG time ago
• The theory goes that they eventually
turned into Black Holes and that’s why
we don’t see them closer by… i.e., the
ones closer by have already turned into
black holes
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Our Astronaut
• Suppose we have an astronaut getting
close to a Black Holeon the surface of a
collapsing star and stays on the surface
as it collapses
• At some point on his watch, say 11:00
the star shrinks past the critical radius
such that the gravitational field
becomes so strong that nothing can
escape
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SHU 11 cont…
• We believe there is a black hole
at the center of our galaxy.
Reading for this??? Actually
quite common…
• Describe Hawking radiation?
• “Event Horizon?”
• Jets of matter…
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Why do we believe in black holes?
• Do they really
exist? What is
the evidence?
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More Notes on Black Holes
• Black holes have been observed and are
now known to be common
• There is a huge black hole at the center
of the milky way with a mass more than
one million times that of our sun
• That supermassive black hole has a star
orbiting it about 2% of the speed of
light which is faster than the average
speed of an electron orbiting the nucleus
of an atom.
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TOE 4
• Black holes ain’t so black.
• Really want to talk about entropy
and the 2nd law of thermodynamics
• Anything with a temperaure (like a
hot poker) emits radiation (light).
• Black holes, like everything in
quantum mechanics, is no different.
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• This is some text
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TOE 3… cont…
• Call the event horizon the
boundary from which light can
just barely escape (or just
barely not escape if you like).
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TOE 4 cont…
• Black holes emit radiation and
particles as if it were a hot
body with a temperature that
only depends on the black hole’s
mass: the higher the mass the
lower the temperature.
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• Figure on page 77 of BHOT.
• This minimum speed is known as
the “escape velocity” and we can
use it for rockets.
• It turns out that we can
calculate the escape velocity for
a star and as the star gets
heavier and denser it gets. this
value goes up
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TOE 3…
• Why can’t light escape? It
moves at the speed of light… it
doesn’t slow down light a
rocket?
• Space is bent so much by the
black hole that the light simply
curves back onto itself enough
so that it can’t escape
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BHOT 8
• Black Hole is a new word, Created in
1969 by Wheeler (year I was born)
• Think of light as a particle, and
therefore affected by gravity
• If you shoot a cannon ball Model of
throwing up a stone in the air. Small
speed  falls back down
• Huge speed, like the space shuttle, it
will leave the gravitational pull of the
earth
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• Eventually, this speed is so high that its
faster than the speed of light!!! Thus
light can’t escape, its pulled back in!
• In other word all the light that a star
emits will fall back into it and no light
escapes, if no light escapes to us it will
look BLACK and its as if the light is
falling back into to a hole. Thus we call
it a BLACK HOLE>
• TOE 3
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The curvature of
the Sun today,
yellow represents
the sun itself
The diagram on
the right Sun
compressed to the
size of a white
dwarf (about the
size of the earth).
Far outside the
sun you can’t really
tell the
difference, but
you can very close
to the sun itself
If the Sun were
compressed into a
black hole…
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Outline
• How are black holes created?
• Properties of black holes
• Why are black holes so
important in cosmology and our
understanding of the Big Bang?
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• The Biggest Objects in the Universe: Part 1
Maybe a week or two on black holes, then a
week on all the other stuff? (Introduce all
the really cool things we study in cosmology
Blackholes, wormholes, supernova, white
dwarfs, pulsars, MACHOs, galaxies, Red
Giants…ect. Is there enough on this stuff… )
Peripheral in SHU and other books. Get the
astronomy book? The toys and the
experiments we use to look at all the cool
things mentioned in the previous
lectures…WMAP, Hubble, Radio
telescopes…ect)
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• The Rest of the Stuff in the
Universe Part 1:(Introduce ideas of
Dark Matter and how we know it is
there, Dark Energy and what it
means for our models of the
universe, talk about experiments
trying to find these things). This
could be where we have our paper
on funding for experiments
searching for Dark Matter!
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TCP 17 cont…
• How black holes are formed
• A black hole originates in the
collapse of the iron core that forms
just prior to the supernova of a
very high mass star
• Any star born with more than about
8MSun dies in a supernova (previous
lecture), but most of the star’s
mass is blown into space by the
explosion.
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• As a result most of the collapsed
cores left behind by most
supernovae become neutron stars
• However, if the supernovae doesn’t
blow away too much of the mass
the remaining neutron star can have
enough mass so that the neutron
pressure cannot overcome gravity
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SHU 5
• Picture of light rays going past
a black hole on page 102
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SHU 10 cont…
• Black Holes continued… Page
210…
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TCP 17 cont…
• Once the critical mass is
reached nothing can hold back
gravity and it collapses on itself
and becomes a black hole.
• This stretches space time
• Cool pictures on page 529
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BHOT 8
• Pictures on page 77 and 81
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• Worm holes a little here… not
sure what to say. Get back to
BHOT first…
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TCP 17 cont…
• Cool picture on page 532 of a
person getting stretched…
• Voyage to a black hole… clocks
slowing down etc. Page 530.
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TOE 3 cont…
• Gravity waves
• Black holes are spherical (like
the earth) in general, but not
all of them are this way.
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How do we Observe Black Holes?
• The amount of mass of a black hole is
huge so it drags stuff into it
gravitationally
• A good analogy would be crumbs on the
surface of the water as it goes down
the sink: swirling faster and faster as it
reaches the drain and gets sucked down.
• As the matter moves more quickly you
can get violent collisions and we can see
this light… Picture on page 220.
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BHOT 8 cont…
• He begins transmitting at 2
seconds before 11:00
• Gravity slows time, so the
stronger the gravity the greater
the effect
• What is one second to the
astronaut will be more than one
second to the spaceship
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• However, they will never see
the one from 11:00
• The light will get “redder” and
redder
• Figure on page 81
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