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Cosmology - PowerPoint PPT Presentation


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Cosmology. What is Cosmology?. Stellar Systems Stellar Clusters Galaxies Galaxy Groups and Clusters Galaxy Superclusters The Universe. Study of the universe as a whole Its past, present, and future Is the Universe finite or infinite? Did it have a beginning? Will it ever end?

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slide1

Cosmology

What is Cosmology?

  • Stellar Systems
  • Stellar Clusters
  • Galaxies
  • Galaxy Groups and Clusters
  • Galaxy Superclusters
  • The Universe
  • Study of the universe as a whole
    • Its past, present, and future
  • Is the Universe finite or infinite?
  • Did it have a beginning?
  • Will it ever end?
  • Where did everything come from?
slide2

The Shape of the Universe

  • In Einstein’s General Theory of Relativity, space and time can be curved
  • The amount of matter and itsmotion affects the curvature ofspace-time
  • If there’s a lot, then theuniverse is like a sphere andfinite: “Closed”
  • If there’s less than that, it’sinfinite: “Open”
  • If there’s just the right amount,it’s infinite: “Flat”
slide3

The Ultimate Number: 

  • The density, denoted , is the amount of stuff in the Universe
  • The critical densityc, is the amount of stuff you need to make the universe flat
  • The ratio is called :(aka 0)
  • If  > 1, universe is closed andfinite
  • If  < 1, universe is open andinfinite
  • If  = 1, universe is flat andinfinite
slide4

What is ? First Attempt

  • Add up contribution from everything we know of:

StuffCont. to 

Stars 0.012

Gas, Dust 0.038

Dark Matter 0.250

Neutrinos 0.001

Total 0.301

  • Total  < 1*
  • Universe is Open*
  • Universe is Infinite*

*It’s lies, all lies

slide5

Hubble Expansion Revisited

  • Universe is expanding
  • In the past, everything was together
  • When was everything together?
  • Will it expand forever?
slide6

Age of the Universe: Round 1

  • To find age of universe, find how long ago any galaxy left us
  • Let its distance be d
  • Hubble’s Law gives us the velocity:v = H0d
  • If you move at constant speed, then: d = vt0
  • Solve for t0:
  • Compare: oldestknown stars
    • About 13 Gyr

What’s wrong with this computation?

A) You assumed constant speed

B) You ignored peculiar velocities

C) Both A and B

D) There’s nothing wrong, this is correct

slide7

Age of the Universe: Round 2

  • We assumed the Universe always expanded at a constant rate
  • But there is gravity
    • Gravity slows things down
  • So the universe was expanding faster in the past
  • Which means it should be younger than we previously calculated
  • The formula gets alittle more complicated:
  • If = 0.30, t0 = 11.7 Gyr
  • If  = 1, t0 = 9.6 Gyr
  • Younger than the oldest stars: The age problem
slide8

Age of the Universe: Round 2

Now

  • If you ignore gravity, you get one age
  • When you include it, universe is younger

No gravity

distance

Matter,  = 1

t = 9.6 Gyr

t = 14.4 Gyr

slide9

Measuring Deceleration

  • White dwarf supernovae are so bright you can see them more than half way across the universe
  • You are seeing the universe at an earlier era
  • Universe may have been expanding at a faster rate
  • Should be able to see this
  • How you do this:
    • Measure distance to very distant WD supernovae
    • Compare to Hubble’s Law
    • Fit to curve for various 
  • Drum roll please . . .
slide10

And the Results Are In

  • No model (with only ordinary matter) worked
  • It looked like universe has recently been accelerating
  • Best fit: Universe decelerated early on, but now accelerating

m = 0.0,  = 0.0

m = 0.3,  = 0.0

m = 1.0,  = 0.0

m = 0.3,  = 0.7

slide11

Dark Energy

  • Universe is currently accelerating
    • This is impossible with ordinary matter or dark matter
  • There must be another unknown contribution to the universe’s gravity
  • This mysterious stuff is called “Dark Energy”
  • We know almost nothing about Dark Energy
  • But dominant view is that it is
    • Cosmological Constant
    • Also known as Vacuum Energy Density
slide12

Vacuum Energy Density

  • Best guess for nature of dark energy is vacuum energy density
  • Particle physics: A combination of relativity and quantum mechanics
  • Predicts you can create particles and anti-particles out of nothingness
    • For a brief time
  • For this reason, “empty” space (the vacuum) has energy
    • We don’t know how to calculate how much
  • Vacuum energy density predicted to have repulsive gravity
    • Empty space repels itself – causes expansion
slide13

What is ? Second Attempt

  • Add up contribution from everything we know of:

StuffCont. to 

Stars 0.012

Gas, Dust 0.038

Dark Matter 0.250

Neutrinos 0.001

Matter Subtotal 0.301

Dark Energy 0.701

Total 1.002

  • Total  = 1, or close*
  • Universe is Flat, or close*
  • Universe is Very Large or Infinite*

*No longer lies

slide14

Age of the Universe: Round 3

  • At present, universal expansion is accelerating
    • Vacuum energy density is the most important contribution
    • Therefore, in the past, the expansion was slower
  • Early on, universal expansion was decelerating
    • Matter had a high concentration and was most important
    • Therefore, early on, the expansion was faster
  • By a numerical coincidence, the average speed is almost exactly the current speed
  • Our first estimate of age was pretty close: t0 = 13.8 Gyr
  • Oldest stars: 13 Gyr
    • No age problem
slide15

Age of the Universe: Round 3

Now

Matter & Energym = 0.3e = 0.7

No gravity

distance

Matter,  = 1

t = 13.8 Gyr

slide16

The Standard Cosmological Model

  • The standard cosmological model: CDM
  • Big bang started it all
  • The universe is formed from:
    • Dark energy ()
    • Cold (slowly moving) dark matter (CDM)
    • Ordinary matter
  • The total density parameter is  = 1 (or close to 1)
  • All structure grew from tiny density perturbations
    • With a simply described distribution
slide17

Composition of the Universe

H0 = 21 km/s/Mly

t0 = 13.8 Gyr

 = 1

slide18

The Future of Expansion

  • “Vacuum” is the biggest part of the mass density now
  • As the universe expands, you have more vacuum, but no more matter – vacuum will be forever the dominant part
  • Vacuum causes universe to accelerate its expansion
  • Universe should expand exponentially – forever
  • Are we sure?
  • No – recall, we don’t know what the dark energy is
  • If it behaves differently, there are other possibilities
    • Modest eternal growth
    • Big Crunch
    • Big Rip
slide19

Cosmic Eschatology – End Times

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • What events will destroy life on Earth?
  • Can we survive the destruction of theEarth?
  • How long can we live around other stars?
  • How long will energy continue to beproduced somewhere in the universe?
  • Current age – 13.8 Gyr = 1.381010 yr
  • Recall: Universe in era of eternalexpansion
slide20

Act 1: Destruction of Life on Earth

  • 100 Myr = 108 yr – Giant Asteroid impact
    • Probably can deflect it with minimal improvement in technology
  • 1 Gyr = 109yr – Runaway Global Warming
    • Sun is gradually getting brighter
    • If it gets too bright, Earth gets like Venus
    • Move Earth (?) or leave for space
  • 5 Gyr = 5109 yr – Sun becomes Red Giant
    • Earth melts, all life eradicated
    • Leave Earth for other stars
  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
slide21

Act 2: Galaxies Merge or Separate

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • 1011 yr – Superclusters or clusters separate from each other

Other

Supercluster

Other

Supercluster

Virgo

Supercluster

SuperGalaxy

Other

Supercluster

Other

Supercluster

  • 1012 yr – All galaxies in a cluster or supercluster merge into super-galaxies
slide22

Act 3: The Stars Die

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • 1014 yr – No gas left for making stars
    • Will have to switch to long lived stars
  • 1014 yr later – Low mass stars die
    • Low mass stars much dimmer
    • They burn fuel more efficiently

What remains – White Dwarfs, Neutron Stars, Black Holes, and Brown Dwarfs

slide23

Act 4: The Galaxies Die

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • 1019 yr – Near collisions of dead stars cause some to get thrown out of galaxy, others thrown into center
    • Black hole at center grows, gets super big
    • Galaxies disappear
slide24

Act 5: Matter Dies

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • 1034 - 1046 yr – Protons and neutrons decay
    • Speculative, but most theorists agree

What remains – Small and large black holes, isolated electrons and anti-electrons

slide25

Act 6: Black Holes Die

  • Giant Asteroids
  • Global Warming
  • Death of Sun
  • Isolated Universe
  • Super Galaxies
  • No New Stars
  • Stars Die
  • Galaxies Evaporate
  • Matter Decays
  • Black Holes Decay
  • According to Quantum mechanics, black holes don’t last forever, they spontaneously emit radiation – very slowly
  • 1060 years – Stellar black holes evaporate
  • 1099 years – Galactic black holes evaporate

What remains – Isolated electrons and anti-electrons in a super-cold universe