Transcript Document 7345367

Modern Nuclear Physics:
Recreating the Creation of the
Universe
Rene Bellwied
Wayne State University
([email protected])
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The Universe and its beginning
Remaining Puzzles in Cosmology
How to recreate creation
The latest evidence
Newton’s Universe Paradox
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The universe is not empty.
 It contains matter with mass.
 Attraction of gravity is present.
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If the universe has existed forever and
is static, (i.e. has no net pattern of
motion), there must be enough time for
gravity to collapse the universe.
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Why did it not happen ?
Why has it not Collapsed?
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Newton knew of 3 ways to resolve this
paradox.
 Universe is infinite in volume and
mass
 Universe is expanding fast enough to
overcome the gravitational attraction.
 Universe has a beginning and/or an
end.
Newton’s Choice…
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Last two ways violate the assumptions
of an eternal and static universe, of
course.
Newton chose the infinite universe
option.
Notice that you are able to arrive at the
conclusion of an infinite universe from
just one observation: the universe is
not empty. No telescopes are needed,
just the ability to follow a train of logical
thought to its conclusion.
Olbers' Paradox
and the Dark Night Sky
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Another simple observation is that the visible
night sky is dark.
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IF the universe is infinite, eternal, and static,
then the sky should be as bright as the
surface of the Sun all of the time!
 Heinrich Olbers (lived 1758--1840)
popularized this paradox in 1826
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This problem is called Olbers' Paradox
(1826).
Statement of the Paradox
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If the universe is
uniformly filled with
stars, then no matter
which direction you look,
your line of sight will
eventually intersect a star
(or other bright thing).
Known that stars are
grouped into galaxies, but
the paradox remains:
your line of sight will
eventually intersect a
galaxy.
How it works….
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The brightnesses of stars does decrease with
greater distance
 remember the inverse square law
BUT there are more stars further out.
 number of stars within a spherical shell around
us increases by the same amount as their
brightness decreases.
Therefore, each shell of stars should have the
same overall luminosity and because there are a
lot of ever bigger shells in an infinite universe,
there should be a lot of light!
An Expanding Universe
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Edwin Hubble and Milton Humason discovered (1920)
that the universe is not static it is expanding.
This is enough to resolve the paradox.
 As the universe expands, the light waves are stretched
out and the energy is reduced.
 Also, the time to receive the light is also lengthened
over the time it took to emit the photon.
Let there be light
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The
HertzsprungRussell
Diagram
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Relation
between mass
and
temperature,
light output,
lifetime.
Stars shine
because of
nuclear fusion
reactions in
their core. The
more luminous
they are, the
more reactions
are taking place
in their cores.
Wien’s Law Temperature
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Cool stars will have the peak of their continuous
spectrum at long (red) wavelengths.
As the temperature of a star increases, the peak of its
continuous spectrum shifts to shorter (blue)
wavelengths.
Doppler Effect
(a)
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Case (a)
 Object (source) moving towards
observer A at velocity “v”
 Observer “A” sees compressed
wave, I.e. shorter wavelength,
higher frequency.
 Observer “B” see stretched
wave, I.e. longer wavelength,
lower frequency.
Case (b)
 Stationary source
 Observer “A” and “B” see same
wavelength.
v
Observer B
Observer A
Source
(b)
Observer B
Observer A
Source
Doppler Effect with Stars
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A star's motion causes a wavelength shift in its light
emission spectrum, which depends on speed and
direction of motion.
If star is moving toward you, the waves are
compressed, so their wavelength is shorter = blueshift.
If the object is moving away from you, the waves are
stretched out, so their wavelength is longer = redshift.
Relativity and Universe Expansion
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This explanation also works if you are moving and
the object is stationary or if both you and the object
are moving.
The doppler effect tells you about the relative motion
of the object with respect to you.
Important fact:
 The spectral lines of nearly all of the galaxies in
the universe are shifted to the red end of the
spectrum.
 This means that the galaxies are moving away
from the Milky Way galaxy.
 This is evidence for the expansion of the universe.
Uniform Expansion
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The Hubble law, speed = Ho × distance, says the
expansion is uniform.
The Hubble constant, Ho, is the slope of the line
relating the speed of the galaxies away from each
other and their distance apart from each other.
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It indicates the rate of the expansion.
If the slope is steep (large Ho), then the expansion rate
is large and the galaxies did not need much time to get
to where they are now.
Hubble Law
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Hubble and Humason (1931):
 the Galactic recession speed = H × distance,
where H is a number now called the Hubble
constant.
This relation is called the Hubble Law and the
Hubble constant is the slope of the line.
Age of the Universe
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Age of the universe can be estimated from the
simple relation of time = distance/speed.
The Hubble Law can be rewritten
 1/Ho = distance/speed.
The Hubble constant tells you the age of the
universe, i.e., how long the galaxies have been
expanding away from each other:
 Age = 1/Ho.
Age upper limit since the expansion has been
slowing down due to gravity.
Some preliminary Conclusions
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Expansion of the universe means that galaxies
were much closer together long ago.
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This implies that there is a finite age to the
universe, it is not eternal.
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Even if the universe is infinite, the light from
places very far away will not have had enough
time to reach us. This will make the sky dark.
Star Count in the Galaxy
Rough guess of the number of stars in our
galaxy obtained by dividing the Galaxy's
total mass by the mass of a typical star (e.g.,
1 solar mass).
 The result is about 200 billion stars!
 The actual number of stars could be several
tens of billions less or more than this
approximate value.
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How stars like the sun evolve
How heavy stars evolve
Black Hole Formation
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After a supernovae explosion, if the core remnant
has a mass greater than 3 solar masses, then not
even the super-compressed degenerate neutrons
can hold the core up against its own gravity.
As the core implodes it briefly makes a neutron
star for just long enough to produce the supernova
explosion. Supernovae are rare (one every 25
years in our galaxy of 200 billion stars!)
Gravity finally wins and compresses everything to
a mathematical point at the center. The point
object is a black hole.
Ultra-strong gravity
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The gravity of the point mass is strong enough
close to the center that nothing can escape, not even
light! Within a certain distance of the point mass,
the escape velocity is greater than the speed of
light.
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The distance at which the escape velocity equals
the speed of light is called the event horizon (or
Schwarzschild radius) because no information
from within that distance of the point mass will be
able to make it to the outside.
Spiral Galaxies
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Andromeda
Galaxy M31 near
the Milky Way.
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NGC 2997 large
face-on spiral
galaxy (Sc).
Masses of Galaxies
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Masses of galaxies are found from the orbital motion of
their stars. Stars in a more massive galaxy orbit faster than
those in a lower mass galaxy because the greater gravity
force of the massive galaxy causes larger accelerations of its
stars.
By measuring the star speeds, one finds out how much
gravity there is in the galaxy. The rotation curve shows how
orbital speeds in a galaxy depend on their distance from the
galaxy's center. Orbital speed is found from the doppler
shifts of the 21-cm line radiation from the atomic hydrogen
gas.
Since gravity depends on mass and distance, knowing the
size of the star orbits enables you to derive the galaxy's
mass.
A Mass Problem
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The stars and gas in most galaxies
move much quicker than expected
from the luminosity of the galaxies.
In spiral galaxies, the rotation curve
remains at about the same value at
great distances from the center (it is
said to be ``flat'').
This means that the enclosed mass
continues to increase even though
the amount of visible, luminous
matter falls off at large distances
from the center.
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Something else must be adding to the gravity of the
galaxies without shining. We call it Dark Matter !
According to measurements it accounts for 90% of the
mass in the universe.
What is Dark Matter ?
We don’t know (yet)
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White dwarfs, brown dwarfs, black holes, massive
neutrinos, although intriguing are very unlikely to account
for most of the dark matter. The dwarfs are generally called
Massive compact halo objects (MACHOS)
New exotic particles or formations are more likely:
 Weakly interacting massive particles (WIMPS)
 Matter based on exotic quark configurations (e.g.
strange Quark matter)
If these states exist somewhere in the universe
wouldn’t they have been produced in the early
universe ?
Evidence for the Big Bang
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Galaxies are distributed fairly uniformily across the sky
between a lot of void (Obler’s paradox)
Background radiation was predicted, and has been found,
to be exactly 2.73 K everywhere in the universe. Variations
as measured by a NASA satellite named COBE (Cosmic
Background Explorer) are less than 0.0001 K.
What happened at the beginning ?
A Cosmic Timeline
Age
0
10-35 s
Energy
1019 GeV
1014 GeV
Matter in universe
grand unified theory of all forces
1st phase transition
(strong: q,g + electroweak: g, l,n)
10-10 s
102 GeV
2nd phase transition
(strong: q,g + electro: g + weak: l,n)
10-5 s
0.2 GeV
3rd phase transition
(strong:hadrons + electro:g + weak: l,n)
3 min.
0.1 MeV
6*105 years 0.3 eV
Now
(15 billion years)
3*10-4 eV = 3 K
nuclei
atoms
The Grand Unification Theory
(GUT)
An Inflationary Universe
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The universe expanded to a point where the
unified forces of nature started to decouple.
When the strong force decoupled a major
amount of energy was released and the
universe expanded by a facto 1030 in less
than 10-36 seconds. This rapid expansion is
called inflation
Going back in time
~ 100 s after Big Bang
Nucleosynthesis begins
~ 10 ms after Big Bang
In the beginning
Hadron Synthesis
quark – gluon strong force binds
quarks and gluons in massive objects:
protons, neutrons mass ~ 1 GeV
plasma
STAR
The RHIC Complex
1. Tandem Van
de Graaff
6
2. Heavy Ion
Transfer Line
3. Booster
5
3
4. Alternating Gradient
Synchrotron (AGS)
4
2
1
5. AGS-to-RHIC
Transfer Line
6. RHIC ring
Let’s go for the ‘Mini-Bang’
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We need a system that is small so that we can
accelerate it to very high speeds.
(99.9% of the speed of light)
But we need a system (i.e. a chunk of matter and
not just a single particle) so that the system can
follow simple rules of thermodynamics and form a
new state of matter in a particular phase.
We use heavy ions (e.g. a Gold ion which is made
of 197 protons and neutrons). It is tiny (about a
10-14 m diameter) but it is a finite volume that can
be exposed to pressure and temperature
What are we trying to do ?
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We try to force a phase transition of the matter we
know (e.g. our Gold nucleus) to a new state of
matter predicted by the Big-Bang, called a QuarkGluon Plasma (QGP)
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We try to do that by following thermodynamics:
PV = nRT
A system of volume V can change if exposed to
pressure P or temperature T.
An example: water, ice, and steam
pressure
This is a simple phase diagram
The temperature inside
The temperature inside a heavy ion collision
at RHIC can exceed 1000 billion degrees !!
 That’s about 10,000 times the temperature
of the sun
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How to create a QGP ?
energy = temperature & density = pressure
Let’s collide two heavy nuclei (1)
Let’s collide two heavy nuclei (2)
What is a Quark-Gluon Plasma?
An atom
contains a
nucleus...
…which
contains
protons and
neutrons...
…which
contain up
and down
quarks.
Let’s study all phases of the process
Freeze-out
Hadron Gas
Phase Transition
Hard
scattering
Plasma-phase
Pre-Equilibrium
If the QGP was formed, it will only live for 10-21 s !!!!
BUT does matter come out of this phase the same way it went in ???
The STAR Experiment
450 scientists from 50 international institutions
Conceptual
Overview
The STAR Experiment
construction from 1992-2000
data taking from 2000-2010 (?)
Overview while
under
construction
The STAR Experiment (TPC)
Construction
in progress
The STAR Experiment (SVT)
Construction
in progress
The STAR Experiment (SVT)
The happy crew
after 8 long years
Actual Collision in STAR (1)
Actual STAR data
for a
peripheral collision
Actual Collision in STAR (2)
Actual STAR data
for a central
collision
What is going on ?
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A Au nucleus consists of 79 protons and 118 neutrons = 197
particles -> 394 particles total
p and n consist of u- and d-quarks
After the collision we measure about 10,000 particles in the
debris!
measured particles: p, p, K, f, L, r, X, W, d, J/y, Y
many particles contain s-quarks, some even c-quarks
Energy converts to matter, but does the matter go through a
phase transition ?
How Do We Measure Things ?
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particles go from the inside-out
they have to traverse certain detectors
they should stop in the outermost detector
the particle should not change its properties when
traversing the inner detector
DETECT but don’t DEFLECT !!!
inner detectors have to be very thin (low radiation
length): easy with gas, challenge with solid state
materials (Silicon).
What do we have to check ?
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If there was a transition to a different phase, then this phase
could only last very shortly. The only evidence we have to check
is the collision debris.
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Check the make-up of the debris:
 which particles have been formed ?
 how many of them ?
 are they emitted statistically (Boltzmann distribution) ?
 what are their kinematics (speed, momentum, angular
distributions) ?
 are they correlated in coordinate or momentum space ?
 do they move collectively ?
Signatures of the QGP phase
Phase transitions are signaled
thermodynamically by a ‘step function’ when
plotting temperature vs. entropy (i.e. # of
degrees of freedom.
The temperature (or energy) is used to
increase the number of degrees of freedom
rather than heat the existing form of matter.
In the simplest approximation the number of
degrees of freedom should scale with the
particle multiplicity.
At the step some signatures drop
and some signatures rise
How do we know what happened ?
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We have to compare to a system that did definitely
not go through a phase transition (a reference
collision)
Two options:
 A proton-proton collision compared to a GoldGold collision does not generate a big enough
volume to generate a plasma phase
 A peripheral Gold-Gold collision compared to a
central one does not generate enough energy
and volume to generate a plasma phase
Time scales of the collision (simulated)
initial state
pre-equilibrium
dN/dt
hadronic phase
and freeze-out
QGP and
hydrodynamic expansion
hadronization
CYM & LGT
Measurements:
HBT
Balance function
Resonances
PCM & clust. hadronization
NFD
NFD & hadronic TM
1 fm/c
5 fm/c
string & hadronic TM
10 fm/c
50 fm/c
time
PCM & hadronic TM
Chemical freeze out
Kinetic freeze out
Time scales according to STAR data
GT
CYM & LGT
Balance function (require flow)
CYM & LGT
Resonance survival
PCM PCM
& &
clust.
clust. hadronization
hadronization
PCM & clust. hadronization
Rout, Rside
NFD
dN/dt
Rlong (and HBT wrt reaction plane)
NFD & hadronic TM
NFD
NFD
NFD & hadronic TM NFD & hadro
string & hadronicstring
TM& hadronic TM
strin
PCM & hadronic
PCM
TM& hadronic
PCM & hadronic TM TM
1 fm/c
5 fm/c
10 fm/c
20 fm/c time
Chemical freeze out
Kinetic freeze out
Evidence: Some particles are suppressed
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If the phase is very dense (QGP) than certain particles get absorbed
If things are produced in pairs then one
might make it out and the other one not.
Peripheral Au + Au
STAR Preliminary
Central Au + Au
If things require the fusion of very heavy
rare quarks they might be suppressed in a
dense medium
Evidence: Some particles are enhanced
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Remember dark matter ? Well, we didn’t find clumps of it yet, but we
found increased production of strange quark particles
What is our present conclusion ?
The interpretation of bulk properties in heavy ion systems is complex. We have
indications of unusual behavior in rare, fast decoupling, and high momentum
probes. Our system behaves like matter, not a collection of elementary particles,
and we have the tools to study it.
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We could declare discovery of the QGP but we have more things to study and
we don’t have the ‘smoking gun’ yet. Further exploration will take a few years,
but the first steps were very exciting and very successful.