big objects and black holes topic 3: properties of black holes big bang, black holes, no math 1 big...

Big Objects and Black HolesTopic 3: Properties of Black Holes

Big Bang, Black Holes, No Math

1

Big Bang, Black Holes, No MathASTR/PHYS 109

Dr. David TobackLecture 24 & 25



2

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 1



3

Was Due Today– L25• Reading:

– Unit 6• Pre-Lecture Reading Questions:

– Unit 6: Stage 1• End-of-Chapter Quizzes:

– Chapter 16• Papers:

– Paper 3 Revision (if desired): Stage 2 due Wednesday

• Honors Papers:– (Stage 2)– Final paper due on the last day of class



4

Unit 5: Big Objects

1.Galaxies2.Star Birth and

Death3.More on Black

HolesToday



5

Where are we now in the history?

Half a billion years after the bangBlack holes start forming



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 6



7

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 Bang



8

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



9

Why do we call it a black hole?

Call it a Black Hole because

light can’t “escape”

Say more about what this

means



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

10



11

No dent in space… Just a small

• 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 black hole?

1.4 Million Kilometers across

~25 Kilometers across



12

Space looks the same, but let’s look at the Curvature

of Space-Time near the SunThe size of the Sun…



13

How the Curvature Changes as we Compress the Sun

What if we compressed the

Sun into a Neutron Star?

Far outside the Sun you can’t really tell the differenceYou can tell the difference if you are very close to the Sun itselfThe sun is now a few kilometers across



14

Compress the Sun into a Black Hole

Infinite curvature

• 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



What does this have to do with light being able

to escape? 15



16

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



The Moon has a “small” escape Velocity

17



The Escape Velocity for the Earth

18



The Sun

19



A Neutron Star

20



A Black Hole

21



22

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 Space-Time



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

23



Later time

Even though he is walking in the “up” direction, his overall motion is actually downwards 24



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” 25



26

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”



27

Black Holes

Light falls in and never comes backLight from inside can’t escape!

Path of light passing nearby gets bent



28

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…



29

Different Types of Black Holes

• Two different types1. 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 four million times that of our sun– At the center of many (all?) large

galaxies



Some pictures from Chapter 2

30



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 only observed in “distant” galaxies31



Switch Topcs

•Life near a black hole

•Evidence for black holes

32



33

Getting a Close-Up Look

What would a Black Hole look like to an observer who tries to get a closer look?



34

The same thing is true for our Astronaut

An Astronaut Near a Black Hole

Light falls in and never comes back



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 EVENT HORIZON

35



36

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



Falling into a Black Hole

Spaghettification as he falls inCan’t see him after he passes the event horizon… not even light from his gun can

escape37



38

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 companion



39

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



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

40



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 41



42

Last Topic on Black Holes…

Why are Black Holes important in Cosmology?



43

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…



44

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…



45

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…



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 46



47

For Next Time – L24• Reading:


– 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 2 due next

Wednesday– Paper 4: Stage 1 due Wednesday if we finished

Chapter 17• Honors Papers:

– (Stage 2)– Final paper due on the last day of class



48



Clicker Question

49

Can you "fill up" a black hole? a) Yesb) No



Clicker Question

50

Can a Black Hole orbit another star?a) Yesb) No



Clicker Question

51

Could the Earth orbit a black hole?a)Yesb)No



Clicker Question

52

What would happen if two black holes collided? a)They would make a

supermassive black holeb)They would just make a

black hole that is the mass of the two black holes that started

c)Black holes can’t collide



1 Paragraph in-class Quiz

What is the evidence for stellar black holes?

53



54



– 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



55


– 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)



56

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



57

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 due Monday before class



58

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



59

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



Early Times & Fate of the Universe Topic 1: Possibilities

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 a paper 4 revision

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61

Prep For Next Time – L11•Reading:–BBBHNM: All reading through Chapter 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.



62

Prep For Next Time – L11•Note: May change depending on how far we

get in lecture•Reading:–BBBHNM: All reading through Chapter 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



63

Prep for Today (Is now due) – L23

• Reading:– BBBHNM 18

• Reading questions:– Chapter 18


• 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



64


• Reading:– BBBHNM 18

• Reading questions:– Chapter 18


• 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



65


• 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



66

Prep For Next Time – L12•Note: May change depending on how far we

get in lecture•Reading:–BBBHNM: All reading through Chapter 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



Prep for Next Time – P23

67

• 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 Chapter 17



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)

68



69

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



70

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



Prep for Next Time – P22

71

• 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



Announcement before we begin

72



73

Time near a Black Hole

The passage of time for an observer near or on a Black Hole is different than we observe because space-time is different in curved space



74

Evidence for Black Holes?

Hubble Space Telescope data

Cygnus XR-1Look at the hot

gas swirling around “Nothing”

A “blob” breaks off then swirls in and disappears like an astronaut would

http://oposite.stsci.edu/pubinfo/pr/2001/03/content/

CygnusXR-1.mpg



75

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



76



•These collisions produce light that we can see



77

The Sun in Space-Time

The size of the Sun…



78

Compressing the Sun

What if we compressed the

Sun into a Neutron Star?

Far outside the Sun you can’t really tell the differenceYou can tell the difference if you are very close to the Sun itselfThe sun is now a few kilometers across



79

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…



80

The Sun in Space-Time

Anything faster than 620 km/sec can escape



81

Neutron Stars

Only things faster than half the speed of light can escape



82

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 quickly



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

83



Other Stuff

•Elearning:–Unit 5 in progress

•Make sure you pick up the latest version of the online textbook!!!–Been updating it all semester

84



85

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) • TOE: Chaps. 1-3



86

For Next TimeUnit 6: Early Times and the Fate of the UniverseFull 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



87

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



88

The Life and Death of Stars

Black Hole

Big Star(Supergiant)

Small Star(Red Giant)

Brown Dwarf

White Dwarf Neutron Star

Slightly more complicated than this…

Explodes (Superno

va)



8989

Writing Assignments

Short Assignments 1 & 2Re-do’s are still possible. Want to revise again? Talk to me

eLearning:Unit 4 now dueNeed to be working on Unit 5



9090

Papers AFTER Paper 2

Two options1.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 PaperIf you want this option Stage 1

must be approved ASAP• Was due last week

• Final paper due the last day of class, Tuesday Dec 8th



91

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



92


•We can “see” Black Holes “eating” other stars

•They are so massive that the gravitational attraction can “suck” off stuff from another star



93

Black Holes ain’t so black…



94

Quantum Mechanics

Weird: Pairs of particles can be created but they have to disappear again quickly because of Quantum Mechanics

e+

e-

Need to conserve energy



95

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-



96

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



97

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…



98

Can we see this?

Example of a Black Hole

•Stuff swirling into the middle

•A stream of particles coming out



99



•These collisions produce light that we can see



100

http://science.nasa.gov/headlines/images/blackhole/blackhole-swirl.jpg



101

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



102

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



103

What is a Black Hole?

•A Black Hole is a really REALLY DENSE star

•REALLY curves the space time around it…



104

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!



105

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!



106

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



107

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



108

That’s it

•It’s been a real pleasure•Stay in touch, and best of luck in the future!



109

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



110

Next Time

•Back to Section 5: Early Times and the Fate of the Universe–Inflation–Dark Energy



111

•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



112

• 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…



113

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



114

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



115

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



116

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



117

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



118

• 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



119

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



120

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…



121

Why do we believe in black holes?

•Do they really exist? What is the evidence?



122

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.



123



124



125



126

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.



127



128

•This is some text



129



130

TOE 3… cont…

•Call the event horizon the boundary from which light can just barely escape (or just barely not escape if you like).



131

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.



132

•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



133



134

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



135

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



136



137

• 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



138

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…



139



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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!



143

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



145

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…



147

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…



150

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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• 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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