Evolution of the Universe
Frank L. H. Wolfs
Department of Physics and Astronomy
University of Rochester
Frank L. H. Wolfs / University of Rochester, Slide 1
Outline
Why do I talk about this topic?
Tools used to probe the evolution of the Universe:
Astronomy
Nuclear Physics
High-Energy Physics
Going back in time in New York State:
The Relativistic Heavy-Ion Collider (RHIC)
Conclusions
Frank L. H. Wolfs / University of Rochester, Slide 2
Why do I talk about this topic?
I am just a nuclear physicist!
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Because I was asked to give a talk about PHOBOS.
Because my primary interest in relativistic heavy-ion
physics is motivated by the astrophysical implications of our
studies of properties of nuclear matter under extreme
conditions.
Because our study of the evolution of the universe is a great
example of how distinct areas of basic science can
contribute different components / solutions to the same
puzzle.
Frank L. H. Wolfs / University of Rochester, Slide 3
What happened during the last
9
15 x 10 years?
Frank L. H. Wolfs / University of Rochester, Slide 4
Going back in time:
Astronomy
Frank L. H. Wolfs / University of Rochester, Slide 5
Nuclear physics allows us to
describe stellar nucleosynthesis
Frank L. H. Wolfs / University of Rochester, Slide 6
The binding energy per nucleon
Source of nuclear energy
Frank L. H. Wolfs / University of Rochester, Slide 7
Nucleosynthesis in stars forms all
elements heavier than Lithium
Death of an “Ordinary” Star
Frank L. H. Wolfs / University of Rochester, Slide 8
Death of a Massive Star
Nucleosynthesis
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Hydrogen
burning
(He
production)
Helium burning (C and O
production)
Carbon, Oxygen, and Neon
burning (16 ≤ A ≤ 28 production)
Silicon burning (28 ≤ A ≤ 60
production)
The s-, r-, and p-processes (A ≥
60 production)
The l-process (D, Li, Be, and B
production)
Frank L. H. Wolfs / University of Rochester, Slide 9
Experimental nuclear physics:
Measuring stellar reaction rates
Converting protons to helium
Frank L. H. Wolfs / University of Rochester, Slide 10
The evolution of stars
Frank L. H. Wolfs / University of Rochester, Slide 11
Formation of heavy elements
(beyond Iron)
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Elements beyond iron are not
formed
in
“lighter-element
burning” reactions (abundances
are too large).
The neutron-rich nuclei in this
region are formed via the sprocess (n capture) and r-process
(b decay).
The proton-rich nuclei in this
region are formed via the pprocess (p capture).
Need nuclear data far from
stability.
Frank L. H. Wolfs / University of Rochester, Slide 12
Better techniques/facilities =>
Better info far from stability
Frank L. H. Wolfs / University of Rochester, Slide 13
Nucleosynthesis is an ongoing
process.
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Nuclei are still being synthesized
in the Universe.
By measuring life times of
unstable nuclei, areas of active
nucleosynthesis can be be
identified.
For example:
26Al has a lifetime of 730,000
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years.
26Al decays by emitting g rays.
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26AL g rays
 The origin of
reveals the locations of active
nucleosynthesis.
Frank L. H. Wolfs / University of Rochester, Slide 14
Data from the GRO satellite
Star Formation:
9
1 x 10 yr after the Big Bang
Molecular clouds of mainly
hydrogen molecules are the
birthplace of stars:
 Dense
regions collapse and
form “protostars”.
 Initially
the
gravitational
energy of the collapsing star is
the source of its energy.
 Once the density of its central
core is large enough, the
hydrogen burning process can
start, and the star becomes a
“main sequence” star.
Frank L. H. Wolfs / University of Rochester, Slide 15
Big-Bang Problem:
Large Scale Structures
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The Big-Bang theory predicts
that
matter
is
uniformly
distributed
throughout
the
universe.
The formation of large-scale
structures requires the formation
of small fluctuations in density
(around 0.5%).
The tiny fluctuations in density
can not be produced by gravity.
Frank L. H. Wolfs / University of Rochester, Slide 16
Cosmic Microwave Background:
Fluctuations in early universe
Microwave background is created
when hydrogen atoms form (about
400,000 years after the Big bang.
Frank L. H. Wolfs / University of Rochester, Slide 17
Cosmic Microwave Background:
Fluctuations in early universe
Observations by COBE have been confirmed by BOOMERANG
with an improved angular resolution (factor of 35).
Frank L. H. Wolfs / University of Rochester, Slide 18
Formation of light nuclei:
Three minutes after the Big Bang
Frank L. H. Wolfs / University of Rochester, Slide 19
Formation of light nuclei:
Three minutes after the Big Bang
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Neutrons and protons interact and
form deuterium.
Tritium
and
Helium
are
subsequently created by neutron
and proton capture.
The reaction rates are high
enough to ensure that most
neutrons will interact before they
decay (neutron life time is 10
minutes).
Using measured reaction rates,
we can calculate the relative
abundance.
Frank L. H. Wolfs / University of Rochester, Slide 20
Formation of light nuclei:
Three minutes after the Big Bang
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All deuterium is created during
this phase.
The
calculated
abundances
depend critically on the density of
baryons (protons and neutrons).
A baryon density of a few percent
is required to account for the
measured abundances. Data limit
the number of light neutrino
generations.
Not all dark matter can be
baryonic.
Critical density
Frank L. H. Wolfs / University of Rochester, Slide 21
Formation of Nucleons
100 µs after the Big Bang
During the first few seconds after the Big Bang the universe
was composed of:
 Nucleons (protons and neutrons).
Any nuclei formed at
this point would not have survived long in this hightemperature environment.
 Leptons (electrons, neutrinos, and photons)
 During this phase baryons, anti-baryons, and photons were
in equilibrium and their abundances were nearly equal.
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 The ratio NB / Ng observed today is 10 .
 This ratio represents the fractional discrepancy between
matter and antimatter during this phase:
 For every one billion anti-baryons there were one billion
and one baryons.
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Frank L. H. Wolfs / University of Rochester, Slide 22
Unanswered Questions about the
Evolution of the Early Universe
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Origin of the density fluctuations:
 Quark-to-Hadron transitions
Matter / anti-matter asymmetry
 Symmetry breaking
Missing mass:
 WIMPS
 Axions
 Neutrinos
Recreation of the “early universe” might
allow us to address these questions.
Frank L. H. Wolfs / University of Rochester, Slide 23
Recreating the early universe:
relativistic heavy-ion collisions
Frank L. H. Wolfs / University of Rochester, Slide 24
Production of the QGP
Relativistic Heavy-Ion Collisions
Two nuclei approach
each other. The nuclei
are contracted to thin
pancakes
Hard collisions
dominate first
instants of
collision
Frank L. H. Wolfs / University of Rochester, Slide 25
Produced particles
reinteract at hard
and soft scales
Final state particles
freeze-out and stream
towards the detectors…
Phases of Nuclear Matter
Nuclear matter can exist in
several phases:
 At low excitations energies,
nuclear matter may evaporate
protons and neutrons.
 At
high temperatures or
densities, a “gas” of nucleons
may form.
 At
extreme
conditions,
individual nucleons may lose
their identities, and the
constituents quarks and gluons
may form a quark-gluon
plasma.
Frank L. H. Wolfs / University of Rochester, Slide 26
Formation of the Quark-Gluon
Plasma (QGP)
Frank L. H. Wolfs / University of Rochester, Slide 27
Relativistic Heavy-Ion Collider:
Scientific Objectives
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To create extraordinary states of
nuclear matter in density and
temperature (similar to matter a
few µs after the Big Bang).
To deconfine the quarks and
gluons and form a Quark-Gluon
Plasma.
Experimental goals @ RHIC
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Frank L. H. Wolfs / University of Rochester, Slide 28
Verify the existence of the
Quark-Gluon Plasma.
Explore the properties of this
new phase of matter.
Study the transitions from
quarks to nucleons (which will
provide insight into the
physics of the early universe).
From BBC News
RHIC is not the end of the world!
Frank L. H. Wolfs / University of Rochester, Slide 29
From ABC News
The Doomsday Machine!
Frank L. H. Wolfs / University of Rochester, Slide 30
Will the world survive the first
collisions at RHIC?
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Suppose a black hole was formed in a head-on collision
between two 100-GeV/A Au ions.
Properties of this black hole (Astronomy 142):
-47 m
 The Schwarzschild radius is 2.1 x 10
 The black hole evaporates via Hawking radiation in about
2.3 x 10-82 s
-74 m
 Before the black hole evaporates, it moves 7 x 10
 The black hole can not acquire additional material before
it evaporates.
Yes !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 There will be life after RHIC.
Frank L. H. Wolfs / University of Rochester, Slide 31
Going back in time by travelling
across New York State.
Frank L. H. Wolfs / University of Rochester, Slide 32
Going back in time by travelling
across New York State.
Frank L. H. Wolfs / University of Rochester, Slide 33
The Relativistic Heavy-Ion Collider
Brookhaven National Laboratory
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Two 3.8 km-long concentric rings
with 6 interaction regions.
Capable of accelerating ions up to Au
(A+A, p+p, and p+A).
Maximum beam energy:
 Au + Au:
100 GeV/u
 p + p:
250 GeV
Design luminosity:
 Au + Au:
2 x 1026 cm-2 s-1
 p + p:
1 x 1031 cm-2 s-1
First running period concluded on
9/19/2000 with a luminosity close to
10% of the design luminosity.
Frank L. H. Wolfs / University of Rochester, Slide 34
Preparing Au ions for injection in
RHIC.
10.8 GeV/u
1 MeV/u
78 MeV/u
Frank L. H. Wolfs / University of Rochester, Slide 35
Conclusions
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Very different areas of basic physics
and astronomy contribute to our
understanding of the evolution of the
universe.
Many unanswered questions may be
understood if we know the properties
of matter under extreme conditions.
This new state of matter is produced
for the first time in New York State.
First results of experiments at RHIC
will be discussed by Prof. Manly on
10/21 at 3.30 pm.
Frank L. H. Wolfs / University of Rochester, Slide 36