Download Lecture 22 - Center for Astrophysics and Space Astronomy CASA

ASTR 1200
Announcements
Last Lecture on
Thursday.
Final Exam Wednesday Dec 17 1:30-4:00
In Benson 180
Josh will hold review 5:30-6:30 here (Benson180)
On Monday (15th)
Website
http://casa.colorado.edu/~wcash/APS1200/APS1200.html
A Modern Hubble Diagram
Galaxies are Flying Apart
Galaxies remain same size. They just get farther apart.
Effect is the same no matter which position you occupy
Expanding Universe
Current Universe
Early Universe
The volume of the universe is
increasing.
The Age of the Universe
v  Hd
1
d 
H

v

d  vt
Notice: At time zero, d = 0
All galaxies are at zero distance!
The universe has zero volume!
when t=1/H
Feeding a Quasar
Accretion disk is formed of stars
and clouds that wander too near the
big black hole.
Tidal forces rip them apart.
They settle into an accretion disk.
When there’s no material falling in,
the quasar goes quiet.
Jets
The Cosmic Web
Structure of the Universe
Where is the center of the Universe?
Where are the edges?
What happens if you fly to the edge and stick your finger through?
Newtonian Universe must be infinite.
Cosmological Principle: The Universe is Everywhere the Same
(when averaged over grand scale)
Classical Universe
•
•
•
•
Euclidean Geometry
Infinite in Extent
Matter may or may not be everywhere
Universe infinitely old
– always been here, always will be
• Expansion still possible
•
2x∞=∞
Cosmological Principle
• Cosmological Principle applied to
expanding Euclidean Universe
• New matter must be formed of nothing to
keep density everywhere the same.
Olber’s Paradox
If universe is infinite with stars everywhere,
then there an infinite number of stars.
Any line of sight will eventually intersect the
surface of star. Sky would be as bright as the
surface of the Sun.
Well it isn’t. So why not?
Universe Must Change
Answer to Olber’s Paradox:
Universe must change:
Space: ie the stars stop
This was the answer until mid 20th Century
Time: Universe hasn’t always been here, so can’t see forever.
Discovery of Big Bang leads us to this answer.
General Relativity
• GR provided an answer
• The presence of matter warps space in on
itself.
• Space is actually DEFINED by the
presence of the matter in it!!!
• Solves the edge problem
• But geometry is no longer Euclidean
Geometry of Universe
Space Curves
in on itself
There’s no path
out!
Curved Space
There is no “edge” but the volume is finite.
Surface of Earth has no end,
but it is finite.
Expands and falls back
Universe starts as pinprick
Expands.
But its below escape velocity.
Hits maximum size.
Then shrinks
The End is the “Big Crunch”
Negatively Curved Universe
Its warped so it cannot close back on itself.
Is infinite in extent.
Open vs Closed
Universe is either open or closed.
If closed:
Positive Curvature
Finite Mass
Finite Lifetime
Finite Volume
If open:
Negative Curvature
Infinite Mass
Infinite Volume
Infinite Lifetime That’s
INFINITY Folks!!!
Astronomers have prejudice in favor of closed universes.
All measurements have been inconclusive. We live near the edge!
Critical Density
• Whether Universe is open or closed
depends on the average DENSITY of
matter.
• Above 10-29 g/cc the universe is closed
• Below 10-29 g/cc the universe is open
• We are very close to that density
• Coincidence?
rcrit is about 1 atom per liter
History and Fate of Universe
Universe is one of these (maybe).
Best Guess Size
• Diameter of Universe is about 1024 times
larger than the part we can see.
• That makes the volume 1072 times larger.
• But still finite
• How big is 1072 ?
Heat Death of Universe
•
•
•
•
If universe is open, then it will last forever
But stars will all burn out 1014 years
Protons decay 1031 years
Orbits will decay into black holes at center
of the galaxies 1060 years
• Giant black holes evaporate 10100 years
• Nothing left but redshifting photons
More on Infinite Universe
• If Cosmological Principle
holds and universe is
infinite, there’s infinite
mass.
• Infinite Planets
• Infinite Earth-like planets
• Infinite planets just like
you.
• Infinite You’s
• Far away: About
10118
10
meters away
The Origin of it All?
• Good Question
• Perhaps a bubble in a hyper-universe
• Perhaps its “unknowable”
• But it appears Universe started as a very
tiny bubble. How small, we don’t know.
The “Planck Era”
• When quantum fluctuations exceed the radius of
the universe our theories are definitely
inadequate.
• R < 10-35m
• t < 10-44 seconds
• Density of Universe > 1093 g/cc
• T > 1032 K
• Then it starts to expand and cool….
The Inflationary Universe
• Idea: Vacuum of space-time created with
excess energy  folded upon itself
• At t=10-37s, T=1028K, starts to relax
• From 10-37 to 10-33s it expands by the
creation of new space.
• Universe expands from 10-28m to 0.1m
• That’s 10cm in 10-33s = 1032m/s
v = 3x1023 c !!!
How Can It Expand
Faster than Light?
• Einstein’s Law says nothing
can travel faster than light.
• Particles in the inflationary
universe aren’t traveling.
• More space comes into
existence between them.
• Before inflation could see
whole universe.
• Since then, can only see a
small part.
Big! Very, Very Big
Because of inflation, universe gets much
bigger  A factor of 1026!
Means now, universe is 1026 times larger
than we can see.
Rvisible = 1026m
Runiverse = 1052m
We are connected to only one part in 1078
of the volume
Maps of Microwave Background
The size of lumps and
blobs set before inflation.
Indicate residual gravity from
parts of the universe we can
no longer see.
Strong evidence that inflation
is on the right track.
The Annihilation Era
• After inflation settles down and resumes normal
expansion
• So hot that matter and anti-matter are in
equilibrium.
• For every 100,000,000 antimatter particles,
there are 100,000,001 matter particles.
• Basic Asymmetry From Planck era is not
understood, but it’s why we’re made of matter.
.001 Seconds
• Jump from 10-33s to 10-3s
• T = 1012K
• Neutrons and Protons now have cooled so
that can annihilate with anti-neutrons and
anti-protons.
• Leave mostly photons and an occasional
particle of matter.
1 Second
• Electrons and Positrons have cooled to
point where they are no longer in
equilibrium. T=1010K
• Create photons.
• One matter particle in hundred million is
left.
• Those are today’s electrons.
Era of Nucleosynthesis
• T = 109 K
• t = 100s
• Hydrogen and Helium form from neutrons
and protons.
• Tiny amounts of Li and Be are created.
• No carbon: density too low for triple alpha
• This is when the initial elements form
The Plasma Era
• From 100s to 100,000 years universe is a
soup of ionized hydrogen and helium
• But its expanding and cooling
• Ends at 100,000years when the
temperature falls below 3000K.
• Hydrogen and Helium nuclei combine with
electrons to form neutral atoms
• At that moment, universe becomes
transparent
Sky Aglow
• At moment of de-ionization, sky is glowing as
blackbody at 3000K (M star)
• Photons released are no longer re-absorbed
• They travel into the universe and are travelling
today
• But they redshift.
• Now 1000 times longer wavelength than then
(makes them microwaves)
The Cosmic Microwave
Background
• Microwave Antenna at Bell Labs – 1965
• Penzias and Wilson
• Microwaves coming from sky, but not Earth.
Uniformly
• Predicted as part of a “Big Bang” by Gamov in
the early 1950’s
• Inescapable proof of the “Big Bang”
• Killed all steady state theories
• Now we’re studying it.
At 100 Million Years
• No Galaxies yet – or perhaps
protogalaxies
• Gas mostly smooth through universe
• Clumps cause gravitational spots that
create even greater density fluctuations.
• Size:
• Remember: Dark matter dominates
Primordial Density Enhancements
Grow
• Now (12.4Billion
years) we have
structure
• Galaxies and clusters
Recap
History and Fate of Universe
Universe is one of these (maybe).
Dark Energy
• Expansion of
Universe is
Accelerating!!!
• Implies New
Inflationary Era
(Why Now?)
• Acceleration takes
energy
New Cosmology
•
•
•
•
70% of mass is Dark Energy (E=mc2)
25% of mass is Dark Matter
3.5% of mass is in Intergalactic Medium
1.5% of mass is regular matter in galaxies
• Together they add to exactly critical density.
• We’re right on the edge of open/closed
• Universe is either finite and very big, or infinite.