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Evolution of the Universe. Frank L. H. Wolfs Department of Physics and Astronomy University of Rochester. 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:
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Evolution of the Universe Frank L. H. Wolfs Department of Physics and Astronomy University of Rochester
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
Why do I talk about this topic?I am just a nuclear physicist! • 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.
Nuclear physics allows us to describe stellar nucleosynthesis
Nucleosynthesis in stars forms all elements heavier than Lithium Death of an “Ordinary” Star Death of a Massive Star
Nucleosynthesis • 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)
Experimental nuclear physics:Measuring stellar reaction rates Converting protons to helium
Formation of heavy elements(beyond Iron) • 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 s-process (n capture) and r-process (b decay). • The proton-rich nuclei in this region are formed via the p-process (p capture). • Need nuclear data far from stability.
Better techniques/facilities =>Better info far from stability
Nucleosynthesis is an ongoing process. • 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 years. • 26Al decays by emitting g rays. • The origin of 26AL g rays reveals the locations of active nucleosynthesis. Data from the GRO satellite
Star Formation:1 x 109 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.
Big-Bang Problem:Large Scale Structures • 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.
Cosmic Microwave Background:Fluctuations in early universe Microwave background is created when hydrogen atoms form (about 400,000 years after the Big bang.
Cosmic Microwave Background:Fluctuations in early universe Observations by COBE have been confirmed by BOOMERANG with an improved angular resolution (factor of 35).
Formation of light nuclei:Three minutes after the Big Bang • 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.
Formation of light nuclei:Three minutes after the Big Bang • 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
Formation of Nucleons100 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 high-temperature environment. • Leptons (electrons, neutrinos, and photons) • During this phase baryons, anti-baryons, and photons were in equilibrium and their abundances were nearly equal. • The ratio NB / Ng observed today is 10-9. • 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.
Unanswered Questions about the Evolution of the Early Universe • 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.
Recreating the early universe:relativistic heavy-ion collisions
Production of the QGPRelativistic Heavy-Ion Collisions Two nuclei approach each other. The nuclei are contracted to thin pancakes Hard collisions dominate first instants of collision 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.
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 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). Relativistic Heavy-Ion Collider:Scientific Objectives
Will the world survive the first collisions at RHIC? • 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): • The Schwarzschild radius is 2.1 x 10-47 m • The black hole evaporates via Hawking radiation in about 2.3 x 10-82 s • Before the black hole evaporates, it moves 7 x 10-74 m • The black hole can not acquire additional material before it evaporates. • Yes !!!!!!!!!!!!!!!!!!!!!!!!!!!!! • There will be life after RHIC.
The Relativistic Heavy-Ion ColliderBrookhaven National Laboratory • 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.
Preparing Au ions for injection in RHIC. 10.8 GeV/u 1 MeV/u 78 MeV/u
Conclusions • 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.
