Sensitivity of Type Ia Supernovae to Electron Capture Rates E
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
UNSTABLE NONRADIAL OSCILLATIONS on HELIUM-BURNING NEUTRON STARS Anthony L
The Astrophysical Journal, 603:252–264, 2004 March 1 # 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A. UNSTABLE NONRADIAL OSCILLATIONS ON HELIUM-BURNING NEUTRON STARS Anthony L. Piro Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106; [email protected] and Lars Bildsten Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106; [email protected] Received 2003 September 18; accepted 2003 November 17 ABSTRACT Material accreted onto a neutron star can stably burn in steady state only when the accretion rate is high (typically super-Eddington) or if a large flux from the neutron star crust permeates the outer atmosphere. For such situations we have analyzed the stability of nonradial oscillations, finding one unstable mode for pure helium accretion. This is a shallow surface wave that resides in the helium atmosphere above the heavier ashes of the ocean. It is excited by the increase in the nuclear reaction rate during the oscillations, and it grows on the timescale of a second. For a slowly rotating star, this mode has a frequency !=ð2Þð20 30 HzÞ½lðl þ 1Þ=21=2, and we calculate the full spectrum that a rapidly rotating (330 Hz) neutron star would support. The short-period X-raybinary4U1820À30 is accreting helium-rich material and is the system most likely to show this unstable mode, especially when it is not exhibiting X-ray bursts. Our discovery of an unstable mode in a thermally stable atmosphere shows that nonradial perturbations have a different stability criterion than the spherically symmetric thermal perturbations that generate type I X-ray bursts. -
The R-Process Nucleosynthesis and Related Challenges
EPJ Web of Conferences 165, 01025 (2017) DOI: 10.1051/epjconf/201716501025 NPA8 2017 The r-process nucleosynthesis and related challenges Stephane Goriely1,, Andreas Bauswein2, Hans-Thomas Janka3, Oliver Just4, and Else Pllumbi3 1Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium 2Heidelberger Institut fr¨ Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany 3Max-Planck-Institut für Astrophysik, Postfach 1317, 85741 Garching, Germany 4Astrophysical Big Bang Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan Abstract. The rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A > 60 stable nuclei observed in nature. Recently, special attention has been paid to neutron star (NS) mergers following the confirmation by hydrodynamic simulations that a non-negligible amount of matter can be ejected and by nucleosynthesis calculations combined with the predicted astrophysical event rate that such a site can account for the majority of r-material in our Galaxy. We show here that the combined contribution of both the dynamical (prompt) ejecta expelled during binary NS or NS-black hole (BH) mergers and the neutrino and viscously driven outflows generated during the post-merger remnant evolution of relic BH-torus systems can lead to the production of r-process elements from mass number A > 90 up to actinides. The corresponding abundance distribution is found to reproduce the∼ solar distribution extremely well. It can also account for the elemental distributions observed in low-metallicity stars. However, major uncertainties still affect our under- standing of the composition of the ejected matter. -
Electron Capture in Stars
Electron capture in stars K Langanke1;2, G Mart´ınez-Pinedo1;2;3 and R.G.T. Zegers4;5;6 1GSI Helmholtzzentrum f¨urSchwerionenforschung, D-64291 Darmstadt, Germany 2Institut f¨urKernphysik (Theoriezentrum), Department of Physics, Technische Universit¨atDarmstadt, D-64298 Darmstadt, Germany 3Helmholtz Forschungsakademie Hessen f¨urFAIR, GSI Helmholtzzentrum f¨ur Schwerionenforschung, D-64291 Darmstadt, Germany 4 National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA 5 Joint Institute for Nuclear Astrophysics: Center for the Evolution of the Elements, Michigan State University, East Lansing, Michigan 48824, USA 6 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA E-mail: [email protected], [email protected], [email protected] Abstract. Electron captures on nuclei play an essential role for the dynamics of several astrophysical objects, including core-collapse and thermonuclear supernovae, the crust of accreting neutron stars in binary systems and the final core evolution of intermediate mass stars. In these astrophysical objects, the capture occurs at finite temperatures and at densities at which the electrons form a degenerate relativistic electron gas. The capture rates can be derived in perturbation theory where allowed nuclear transitions (Gamow-Teller transitions) dominate, except at the higher temperatures achieved in core-collapse supernovae where also forbidden transitions contribute significantly to the rates. There has been decisive progress in recent years in measuring Gamow-Teller (GT) strength distributions using novel experimental techniques based on charge-exchange reactions. These measurements provide not only data for the GT distributions of ground states for many relevant nuclei, but also serve as valuable constraints for nuclear models which are needed to derive the capture rates for the arXiv:2009.01750v1 [nucl-th] 3 Sep 2020 many nuclei, for which no data exist yet. -
Star Factories: Nuclear Fusion and the Creation of the Elements
Star Factories: Nuclear Fusion and the Creation of the Elements Science In the River City workshop 3/22/11 Chris Taylor Department of Physics and Astronomy Sacramento State Introductions! Science Content Standards, Grades 9 - 12 Earth Sciences: Earth's Place in the Universe 1.e ''Students know the Sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium.'' 2.c '' Students know the evidence indicating that all elements with an atomic number greater than that of lithium have been formed by nuclear fusion in stars.'' Three topics tonight: 1) how do we know all the heavier elements are made in stars? (Big Bang theory) 2) How do stars make elements as heavy as or less heavy than iron? (Stellar nucleosynthesis) 3) How do stars make elements heavier than iron? (Supernovae) Big Bang Nucleosynthesis The Big Bang theory predicts that when the universe first formed, the only matter that existed was hydrogen, helium, and very tiny amounts of lithium. If this is true, then all other elements must have been created in stars. Astronomers use spectroscopy to examine the light emitted by distant stars to determine what kinds of atoms are in them. We've learned that most stars contain nearly every element in the periodic table. The spectrum of the Sun In order to measure measure what kinds of atoms were around in the earliest days of the Universe, we look for stars that were made out of fresh, primordial gas. The closest we can get to this is looking at dwarf galaxies, which show extremely low levels of elements heavier than helium. -
Heavy Element Nucleosynthesis
Heavy Element Nucleosynthesis A summary of the nucleosynthesis of light elements is as follows 4He Hydrogen burning 3He Incomplete PP chain (H burning) 2H, Li, Be, B Non-thermal processes (spallation) 14N, 13C, 15N, 17O CNO processing 12C, 16O Helium burning 18O, 22Ne α captures on 14N (He burning) 20Ne, Na, Mg, Al, 28Si Partly from carbon burning Mg, Al, Si, P, S Partly from oxygen burning Ar, Ca, Ti, Cr, Fe, Ni Partly from silicon burning Isotopes heavier than iron (as well as some intermediate weight iso- topes) are made through neutron captures. Recall that the prob- ability for a non-resonant reaction contained two components: an exponential reflective of the quantum tunneling needed to overcome electrostatic repulsion, and an inverse energy dependence arising from the de Broglie wavelength of the particles. For neutron cap- tures, there is no electrostatic repulsion, and, in complex nuclei, virtually all particle encounters involve resonances. As a result, neutron capture cross-sections are large, and are very nearly inde- pendent of energy. To appreciate how heavy elements can be built up, we must first consider the lifetime of an isotope against neutron capture. If the cross-section for neutron capture is independent of energy, then the lifetime of the species will be ( )1=2 1 1 1 µn τn = ≈ = Nnhσvi NnhσivT Nnhσi 2kT For a typical neutron cross-section of hσi ∼ 10−25 cm2 and a tem- 8 9 perature of 5 × 10 K, τn ∼ 10 =Nn years. Next consider the stability of a neutron rich isotope. If the ratio of of neutrons to protons in an atomic nucleus becomes too large, the nucleus becomes unstable to beta-decay, and a neutron is changed into a proton via − (Z; A+1) −! (Z+1;A+1) + e +ν ¯e (27:1) The timescale for this decay is typically on the order of hours, or ∼ 10−3 years (with a factor of ∼ 103 scatter). -
Fundamentals of Stellar Evolution Theory: Understanding the HRD
Fundamentals of Stellar Evolution Theory: Understanding the HRD By C E S A R E C H I O S I Department of Astronomy, University of Padua, Vicolo Osservatorio 5, 35122 Padua, Italy Published in: "Stellar Astrophysics for the Local Group: a First Step to the Universe" VIII Canary Islands Winter School Cambridge University Press 25 March, 1997 Abstract. We summarize the results of stellar evolution theory for single stars that have been obtained over the last two decades, and compare these results with the observations. We discuss in particular the effect of mass loss by stellar winds during the various evolutionary stages of stars that are affected by this phenomenon. In addition, we focus on the problem of mixing in stellar interiors calling attention on weak aspects of current formulations and presenting plausible alternatives. Finally, we survey some applications of stellar models to several areas of modern astrophysics. 1. Introduction The major goal of stellar evolution theory is the interpretation and reproduction of the Hertzsprung-Russell Diagram (HRD) of stars in different astrophysical environments: solar vicinity, star clusters of the Milky Way and nearby galaxies, fields in external galaxies. The HRD of star clusters, in virtue of the small spread in age and composition of the component stars, is the classical template to which stellar models are compared. If the sample of stars is properly chosen from the point of view of completeness, even the shortest lived evolutionary phases can be tested. The HRD of field stars, those in external galaxies in particular, contains much information on the past star formation history. -
Nucleosynthesis
Nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons. The first nuclei were formed about three minutes after the Big Bang, through the process called Big Bang nucleosynthesis. Seventeen minutes later the universe had cooled to a point at which these processes ended, so only the fastest and simplest reactions occurred, leaving our universe containing about 75% hydrogen, 24% helium, and traces of other elements such aslithium and the hydrogen isotope deuterium. The universe still has approximately the same composition today. Heavier nuclei were created from these, by several processes. Stars formed, and began to fuse light elements to heavier ones in their cores, giving off energy in the process, known as stellar nucleosynthesis. Fusion processes create many of the lighter elements up to and including iron and nickel, and these elements are ejected into space (the interstellar medium) when smaller stars shed their outer envelopes and become smaller stars known as white dwarfs. The remains of their ejected mass form theplanetary nebulae observable throughout our galaxy. Supernova nucleosynthesis within exploding stars by fusing carbon and oxygen is responsible for the abundances of elements between magnesium (atomic number 12) and nickel (atomic number 28).[1] Supernova nucleosynthesis is also thought to be responsible for the creation of rarer elements heavier than iron and nickel, in the last few seconds of a type II supernova event. The synthesis of these heavier elements absorbs energy (endothermic process) as they are created, from the energy produced during the supernova explosion. Some of those elements are created from the absorption of multiple neutrons (the r-process) in the period of a few seconds during the explosion. -
S-Process Nucleosynthesis
Nuclei in the cosmos 13.01.2010 Max Goblirsch Advisor: M.Asplund Recap: Basics of nucleosynthesis past Fe Nuclear physics of the s-process . S-process reaction network . Branching and shielding S-process production sites . Components of the s-process . Basics of TP-AGB stars . Formation of the 13C-pocket . Resulting Abundances Summary References 13.01.2010 s-process nucleosynthesis Max Goblirsch 2 For elements heavier than iron, creation through fusion is an endothermic process The coulomb repulsion becomes more and more significant with growing Z This impedes heavy element creation through primary burning or charged particle reactions 13.01.2010 s-process nucleosynthesis Max Goblirsch 3 Neutron captures are not hindered by coulomb repulsion Main mechanism: seed elements encounter an external neutron flux 2 primary contributions, r(rapid) and s(slow) processes identified . Main difference: neutron density Additional p-process: proton capture, insignificant for high Z 13.01.2010 s-process nucleosynthesis Max Goblirsch 4 R-process basics: . high neutron densities (>1020 cm-3 ) . Very short time scales (seconds) . Moves on the neutron rich side of the valley of stability . Stable nuclides reached through beta decay chains after the neutron exposure . Final abundances very uniform in all stars 13.01.2010 s-process nucleosynthesis Max Goblirsch 5 S-process basics: . Neutron densities in the order of 106-1011 cm-3 . Neutron capture rates much lower than beta decay rates After each neutron capture, the product nucleus has time -
Lecture 3: Nucleosynthesis
Geol. 655 Isotope Geochemistry Lecture 3 Spring 2003 NUCLEOSYNTHESIS A reasonable starting point for isotope geochemistry is a determination of the abundances of the naturally occurring nuclides. Indeed, this was the first task of isotope geochemists (though those engaged in this work would have referred to themselves simply as physicists). We noted this began with Thomson, who built the first mass spectrometer and discovered Ne consisted of 2 isotopes (actually, it consists of three, but one of them, 21Ne is very much less abundant than the other two, and Thomson’s primitive instrument did not detect it). Having determined the abundances of nu- clides, it is natural to ask what accounts for this distribution, and even more fundamentally, what processes produced the elements. This process is known as nucleosynthesis. The abundances of naturally occurring nuclides is now reasonably, though perhaps not perfectly, known. We also have what appears to be a reasonably successful theory of nucleosynthesis. Physi- cists, like all scientists, are attracted to simple theories. Not surprisingly then, the first ideas about nucleosynthesis attempted to explain the origin of the elements by single processes. Generally, these were thought to occur at the time of the Big Bang. None of these theories was successful. It was re- ally the astronomers, accustomed to dealing with more complex phenomena than physicists, who suc- cessfully produced a theory of nucleosynthesis that involved a number of processes. Today, isotope geochemists continue to be involved in refining these ideas by examining and attempting to explain isotopic variations occurring in some meteorites. The origin of the elements is an astronomical question, perhaps even more a cosmological one. -
The Single Degenerate Progenitor Scenario for Type Ia Supernovae and the Convective Urca Process
The Single Degenerate Progenitor Scenario for Type Ia Supernovae and the Convective Urca Process ADissertationpresented by Donald Eugene Willcox to The Graduate School in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics Stony Brook University August 2018 Stony Brook University The Graduate School Donald Eugene Willcox We, the dissertation committe for the above candidate for the Doctor of Philosophy degree, hereby recommend acceptance of this dissertation Alan Calder – Dissertation Advisor Associate Professor, Physics and Astronomy Michael Zingale – Chairperson of Defense Associate Professor, Physics and Astronomy Joanna Kiryluk – Committee Member Associate Professor, Physics and Astronomy Matthew Reuter – External Committee Member Assistant Professor, Applied Mathematics and Statistics This dissertation is accepted by the Graduate School Charles Taber Dean of the Graduate School ii Abstract of the Dissertation The Single Degenerate Progenitor Scenario for Type Ia Supernovae and the Convective Urca Process by Donald Eugene Willcox Doctor of Philosophy in Physics Stony Brook University 2018 This dissertation explores the e↵ects of properties of the progenitor massive white dwarf (WD) on thermonuclear (Type Ia) supernovae. It includes a study of explosions from “hy- brid” C/O/Ne progenitors and focuses primarily on the convective Urca process occurring in C/O progenitors shortly before their explosion. Pre-supernova WDs approaching the Chan- drasekhar mass can possess sufficiently high central densities that 23Na synthesized via 12C fusion undergoes electron capture to 23Ne. Convection sweeps 23Ne to regions of lower den- sity where it reverts via beta decay to 23Na, and vice versa. Cyclic weak nuclear processes of this type constitute the convective Urca process in WDs. -
12.744/12.754 Lecture 2: Cosmic Abundances, Nucleosynthesis and Element Origins
12.744/12.754 Lecture 2: Cosmic Abundances, Nucleosynthesis and Element Origins Our intent is to shed further light on the reasons for the abundance of the elements. We made progress in this regard when we discussed nuclear stability and nuclear binding energy explaining the zigzag structure, along with the broad maxima around Iron and Lead. The overall decrease with mass, however, arises from the creation of the universe, and the fact that the universe started out with only the most primitive building blocks of matter, namely electrons, protons and neutrons. The initial explosion that created the universe created a rather bland mixture of just hydrogen, a little helium, and an even smaller amount of lithium. The other elements were built from successive generations of star formation and death. The Origin of the Universe It is generally accepted that the universe began with a bang, not a whimper, some 15 billion years ago. The two most convincing lines of evidence that this is the case are observation of • the Hubble expansion: objects are receding at a rate proportional to their distance • the cosmic microwave background (CMB): an almost perfectly isotropic black-body spectrum Isotopes 12.7444/12.754 Lecture 2: Cosmic Abundances, Nucleosynthesis and Element Origins 1 In the initial fraction of a second, the temperature is so hot that even subatomic particles fall apart into their constituent pieces (quarks and gluons). These temperatures are well beyond anything achievable in the universe since. As the fireball expands, the temperature drops, and progressively higher level particles are manufactured. By the end of the first second, the temperature has dropped to a mere billion degrees or so, and things are starting to get a little more normal: electrons, neutrons and protons can now exist. -
Nucleosynthetic Isotope Variations of Siderophile and Chalcophile
Reviews in Mineralogy & Geochemistry Vol.81 pp. 107-160, 2016 3 Copyright © Mineralogical Society of America Nucleosynthetic Isotope Variations of Siderophile and Chalcophile Elements in the Solar System Tetsuya Yokoyama Department of Earth and Planetary Sciences Tokyo Institute of Technology Ookayama, Tokyo 152-885 Japan [email protected] Richard J. Walker Department of Geology University of Maryland College Park, MD 20742 USA [email protected] INTRODUCTION Numerous investigations have been devoted to understanding how the materials that contributed to the Solar System formed, were incorporated into the precursor molecular cloud and the protoplanetary disk, and ultimately evolved into the building blocks of planetesimals and planets. Chemical and isotopic analyses of extraterrestrial materials have played a central role in decoding the signatures of individual processes that led to their formation. Among the elements studied, the siderophile and chalcophile elements are crucial for considering a range of formational and evolutionary processes. Consequently, over the past 60 years, considerable effort has been focused on the development of abundance and isotopic analyses of these elements in terrestrial and extraterrestrial materials (e.g., Shirey and Walker 1995; Birck et al. 1997; Reisberg and Meisel 2002; Meisel and Horan 2016, this volume). In this review, we consider nucleosynthetic isotopic variability of siderophile and chalcophile elements in meteorites. Chapter 4 provides a review for siderophile and chalcophile elements in planetary materials in general (Day et al. 2016, this volume). In many cases, such variability is denoted as an “isotopic anomaly”; however, the term can be ambiguous because several pre- and post- Solar System formation processes can lead to variability of isotopic compositions as recorded in meteorites.