DOCSLIB.ORG

Gamma Ray Bursts and Delayed Quark-Deconfinement

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Gamma Ray Bursts and Delayed Quark-Deconfinement GAMMA RAY BURSTS AND DELAYED QUARK-DECONFINEMENT Ignazio Bombaci, Irene Parenti, and Isaac Vida˜na Dipartimento di Fisica “E. Fermi”, Universita‘ di Pisa & INFN, Sezione di Pisa, via Buonarroti, 2, I-56127, Pisa, Italy Abstract We describe a new model, proposed by Berezhiani et al. (2003), which is able to explain how a gamma-ray burst (GRB) can take place days or years after a supernova explosion. We show that above a threshold value of the gravitational mass a pure hadronic star (“neutron star”) is metastable to the conversion into a quark star (hybrid star or strange star), i.e. a star made at least in part of decon- fined quark matter. The stellar conversion process can be delayed if finite size effects at the interface between hadronic and deconfined quark matter phases are taken into account. A huge amount of energy, on the order of 1052 – 1053 ergs, is released during the conversion process and can produce a powerful gamma- ray burst. The delay between the supernova explosion generating the metastable neutron star and the new collapse can explain the delay inferred in GRB 990705 and in GRB 011211. Next, we explore the consequences of the metastability of “massive” neutron stars and of the existence of stable compact quark stars on the concept of limiting mass of compact stars. Finally, we discuss the implica- tions of the present scenario on the interpretation of the stellar mass and radius extracted from the spectra of several X-ray compact sources. Keywords: Gamma rays: Gamma Ray Burst. Stars: Neutron Stars, Strange Stars. Dense Matter: equation of state, quark matter. 1. Introduction Gamma Ray Bursts (GRBs) are one of the most violent and mysterious phe- nomena in the universe which have challenged astrophysicists for decades (see e.g. (Piran 1999; Dermer 2001; Zhang & Meszaros 2003) for a general intro- duction on this subject). During the last ten years a large amount of new obser- vational data, collected by a variety of instruments on board of various satel- lites, has revolutionized our understanding of GRBs. The Burst And Transient Source Experiment (BATSE) on board of the Compton Gamma Ray Observa- tory (CGRO) has demonstrated that GRBs originate at cosmological distances. The BeppoSAX satellite discovered the X-ray “afterglow”. This has permitted 353 D. Blaschke and D. Sedrakian (eds.), Superdense QCD Matter and Compact Stars, 353–375. C 2006 Springer. Printed in the Netherlands. 354 SUPERDENSE QCD MATTER AND COMPACT STARS to determine the position of some GRBs, to identify the host galaxy and, in a number of cases, to measure the red-shift. Accurate determination of the GRB distance from the measured red-shifts, permitted, for the first time, to derive the energy Eγ emitted by the GRB. The measured fluency of the bursts implies an energy of the order of 1053 erg in the case of isotropic emission. There is now, however, compelling evidence that the γ-ray emission is not isotropic, but displays a jet-like geometry. For these bursts, the geometrically corrected gamma-ray energy is about 1051 erg (Frayl et al. 2001). The time duration Tγ of GRBs appears to have a bimodal distribution. Thus, according to their time duration, GRBs are classified as “short” GRBs when Tγ < 2 seconds, and “long” GRBs when Tγ > 2 s. Long GRBs represent about 75% of the total GRB population. It is believed that the two types of GRBs may have different progenitors. Many cosmological models for the energy source (the so-called central en- gine) of GRBs have been proposed. Presently some of the most popular mod- els are: the collapsar (hypernova) model, the merging of two neutron stars (or a neutron star and a black hole) in a binary system, the strong-magnetized millisecond pulsar model, the supranova model. Here, we will not discuss the various merits and drawbacks of the many theoretical models for the GRB cen- tral engine, and we refer the reader to recent review papers on this subject (e.g. Piran 1999; Dermer 2001; Zhang & Meszaros 2003)). In the following, we will report some recent research (Berezhiani et al. 2003; Bombaci et al. 2003) which try to make a connection between GRBs and quark-deconfinement phase transition. 1.1 The delayed Supernova–GRB connection A mounting number of observational data suggest a clear connection be- tween supernova (SN) explosions and GRBs (Bloom et al. 1999; Amati et al. 2000; Antonelli et al. 2000: Piro et al. 2000; Reeves et al. 2002; Hjorth et al. 2003; Butler et al. 2003). The detection of X-ray spectral features in the X-ray afterglow of several GRBs, has given evidence for a possible time delay between the SN explosion and the associated GRB. Particularly, in the case of the gamma ray burst of July 5, 1999 (GRB990705) and in the case of GRB011211, it has been possible to estimate the time delay between the two events. For GRB990705 the supernova explosion is evaluated to have occurred a few years before the GRB (Amati et al. 2000; Lazzati et al. 2001), while for GRB011211 about four days before the burst (Reeves et al. 2002). The scenario which emerges from these findings is the following two-step scenario. The first event is the supernova explosion which forms a compact stellar remnant, i.e. a neutron star (NS); the second catastrophic event is as- sociated with the NS and it is the energy source for the observed GRB. These Gamma Ray Bursts and delayed Quark-deconfinement 355 new observational data, and the two-step scenario outlined above, poses se- vere problems for most of the current theoretical models for the central energy source of GRBs. The main difficulty of all these models is to understand the origin of the second “explosion”, and to explain the long time delay between the two events. In the so-called supranova model (Vietri & Stella 1998) for GRBs the sec- ond catastrophic event is the collapse to a black hole of a supramassive neu- tron star, i.e. a fast rotating NS with a baryonic mass MB above the maximum baryonic mass MB,max for non-rotating configurations. In this model, the time delay between the SN explosion and the GRB is equal to the time needed by the fast rotating newly formed neutron star to get rid of angular momentum and to reach the limit for instability against quasi-radial modes where the collapse to a black hole occurs (Datta et al. 1998). The supranova model needs a fine tuning in the initial spin period Pin and baryonic stellar mass MB,in to pro- duce a supramassive neutron star that can be stabilized by rotation up to a few years. For example, if Pin ≥ 1.5 ms, then the newborn supramassive neutron star must be formed within ∼ 0.03M above MB,max (Datta et al. 1998). 1.2 The nature of Neutron Stars: Hadronic Stars or Quark Stars? One of the most fascinating enigma in modern astrophysics concerns the true nature of the ultra-dense compact objects called neutron stars. Different models for the EOS of dense matter predict a neutron star maximum mass (Mmax) in the range of 1.4 – 2.2 M, and a corresponding central density in 14 3 range of 4 – 8 times the saturation density (ρ0 ∼ 2.8 × 10 g/cm ) of nuclear matter (e.g. Shapiro & Teukolsky 1983; Haensel 2003). In the case of a star with M ∼ 1.4 M, different EOS models predict a radius in the range of 7 – 16 km (Shapiro & Teukolsky 1983; Haensel 2003; Dey et al. 1998). In a simplistic and conservative picture the core of a neutron star is modeled as a uniform fluid of neutron rich nuclear matter in equilibrium with respect to the weak interaction (β-stable nuclear matter). However, due to the large value of the stellar central density and to the rapid increase of the nucleon chemical potentials with density, hyperons (Λ, Σ−, Σ0, Σ+, Ξ− and Ξ0 particles) are expected to appear in the inner core of the star. Other exotic phases of hadronic matter such as a Bose-Einstein condensate of negative pion (π−)ornegative kaon (K−) could be present in the inner part of the star. According to Quantum Chromodynamics (QCD) a phase transition from hadronic matter to a deconfined quark phase should occur at a density of a few times nuclear matter saturation density. Consequently, the core of the more massive neutron stars is one of the best candidates in the Universe where such deconfined phase of quark matter (QM) could be found. Since β-stable hadronic matter posses two conserved “charges” (i.e., electric charge and baryon 356 SUPERDENSE QCD MATTER AND COMPACT STARS number) the quark-deconfinement phase transition proceeds through a mixed phase over a finite range of pressures and densities according to the Gibbs’ criterion for phase equilibrium (Glendenning 1992). At the onset of the mixed phase, quark matter droplets form a Coulomb lattice embedded in a sea of hadrons and in a roughly uniform sea of electrons and muons. As the pressure increases various geometrical shapes (rods, plates) of the less abundant phase immersed in the dominant one are expected. Finally the system turns into uni- form quark matter at the highest pressure of the mixed phase (Heiselberg et al. 1993; Voskresensky et al. 2003). Compact stars which possess a “quark matter core” either as a mixed phase of deconfined quarks and hadrons or as a pure quark matter phase are called Hybrid Neutron Stars or shortly Hybrid Stars (HyS) (Glendenning 1996). In the following of this paper, the more con- ventional neutron stars in which no fraction of quark matter is present, will be referred to as pure Hadronic Stars (HS).
Load more

Recommended publications
  • Collapsing Supra-Massive Magnetars: Frbs, the Repeating FRB121102 and Grbs
    J. Astrophys. Astr. (2018) 39:14 © Indian Academy of Sciences https://doi.org/10.1007/s12036-017-9499-9 Review Collapsing supra-massive magnetars: FRBs, the repeating FRB121102 and GRBs PATRICK DAS GUPTA∗ and NIDHI SAINI Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India. ∗Corresponding author. E-mail: [email protected], [email protected] MS received 30 August 2017; accepted 3 October 2017; published online 10 February 2018 Abstract. Fast Radio Bursts (FRBs) last for ∼ few milli-seconds and, hence, are likely to arise from the gravitational collapse of supra-massive, spinning neutron stars after they lose the centrifugal support (Falcke & Rezzolla 2014). In this paper, we provide arguments to show that the repeating burst, FRB 121102, can also be modeled in the collapse framework provided the supra-massive object implodes either into a Kerr black hole surrounded by highly magnetized plasma or into a strange quark star. Since the estimated rates of FRBs and SN Ib/c are comparable, we put forward a common progenitor scenario for FRBs and long GRBs in which only those compact remnants entail prompt γ -emission whose kick velocities are almost aligned or anti-aligned with the stellar spin axes. In such a scenario, emission of detectable gravitational radiation and, possibly, of neutrinos are expected to occur during the SN Ib/c explosion as well as, later, at the time of magnetar implosion. Keywords. FRBs—FRB 121102—Kerr black holes—Blandford–Znajek process—strange stars—GRBs— pre-natal kicks. 1. Introduction 43% linear polarization and 3% circular polarization (Petroff et al.
    [Show full text]
  • Ucalgary 2017 Welbankscamar
    University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2017 Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh Welbanks Camarena, Luis Carlos Welbanks Camarena, L. C. (2017). Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/27339 http://hdl.handle.net/11023/3972 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh by Luis Carlos Welbanks Camarena A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN PHYSICS AND ASTRONOMY CALGARY, ALBERTA JULY, 2017 c Luis Carlos Welbanks Camarena 2017 Abstract Superluminous supernovae are explosions in the sky that far exceed the luminosity of standard supernova events. Their discovery shattered our understanding of stellar evolution and death. Par- ticularly, the discovery of ASASSN-15lh a monstrous event that pushed some of the astrophysical models to the limit and discarded others. In this thesis, I recount the photometric and spectroscopic signatures of superluminous super- novae, while discussing the limitations and advantages of the models brought forward to explain them.
    [Show full text]
  • Mass-Radius Relation of Compact Stars with Quark Matter INT Summer Program "QCD and Dense Matter: from Lattices to Stars", June 2004, INT, Seattle, Washington, USA
    Mass-Radius Relation of Compact Stars with Quark Matter INT Summer Program "QCD and Dense Matter: From Lattices to Stars", June 2004, INT, Seattle, Washington, USA JurgenÄ Schaffner{Bielich Institut furÄ Theoretische Physik/Astrophysik J. W. Goethe UniversitÄat Frankfurt am Main { p.1 Phase Diagram of QCD T early universe RHIC Tc Quark-Gluon Plasma Hadrons Color Superconductivity nuclei neutron stars µ mN / 3 c µ ² Early universe at zero density and high temperature ² neutron star matter at zero temperature and high density ² lattice gauge simulations at ¹ = 0: phase transition at Tc ¼ 170 MeV { p.2 Neutron Stars ² produced in supernova explosions (type II) ² compact, massive objects: radius ¼ 10 km, mass 1 ¡ 2M¯ 14 3 ² extreme densities, several times nuclear density: n À n0 = 3 ¢ 10 g/cm { p.3 Masses of Pulsars (Thorsett and Chakrabarty (1999)) ² more than 1200 pulsars known ² best determined mass: M = (1:4411 § 0:00035)M¯ (Hulse-Taylor-Pulsar) ² shortest rotation period: 1.557 ms (PSR 1937+21) { p.4 ² n = 104 ¡ 4 ¢ 1011 g/cm3: outer crust or envelope (free e¡, lattice of nuclei) ² n = 4 ¢ 1011 ¡ 1014 g/cm3: Inner crust (lattice of nuclei with free neutrons and e¡) Structure of Neutron Stars — the Crust (Dany Page) ² n · 104 g/cm3: atmosphere (atoms) { p.5 ² n = 4 ¢ 1011 ¡ 1014 g/cm3: Inner crust (lattice of nuclei with free neutrons and e¡) Structure of Neutron Stars — the Crust (Dany Page) ² n · 104 g/cm3: atmosphere (atoms) ² n = 104 ¡ 4 ¢ 1011 g/cm3: outer crust or envelope (free e¡, lattice of nuclei) { p.5 Structure of Neutron
    [Show full text]
  • Cosmic Matter Under Extreme Conditions: CSQCD II Summary
    Compact stars in the QCD phase diagram II (CSQCD II) May 20-24, 2009, KIAA at Peking University, Beijing - P. R. China http://vega.bac.pku.edu.cn/rxxu/csqcd.htm Cosmic Matter under Extreme Conditions: CSQCD II Summary Jochen Wambach Institut f¨ur Kernphysik Technical University Darmstadt Schlossgartenstr. 9 D-64289 Darmstadt Germany Email: [email protected] Abstract After the first meeting in Copenhagen in 2001 QSQCD II is the second workshop in this series dealing with cosmic matter at very high density and its astrophysical implications. The aim is to bring together reseachers in the physics of compact stars, both theoretical and observational. Consequently a broad range of topics was presented, reviewing extremely energetic cosmolog- ical events and their relation to the high-density equation of state of strong- interaction matter. This summary elucidates recent progress in the field, as presented by the participants, and comments on pertinent questions for future developments. 1 Introduction Compact stars such as white dwarfs, neutron stars or black holes are the densest objects in the Universe. They are the final product of stellar evolution. Which object is formed depends on the mass of the progenitor star. Since at least half of the stars in our galaxy are bound in pairs one is often dealing with binary systems with interesting evolution histories such as merger events or complex accretion phenomena. Neutron- hyprid- or quark stars are the most compact objects without an event horizon. Their observational signatures, composition and evolution and arXiv:0912.0100v1 [astro-ph.SR] 1 Dec 2009 the relation to states of strong-interaction matter was the major focus of this workshop.
    [Show full text]
  • Astrophysics
    Publications of the Astronomical Institute rais-mf—ii«o of the Czechoslovak Academy of Sciences Publication No. 70 EUROPEAN REGIONAL ASTRONOMY MEETING OF THE IA U Praha, Czechoslovakia August 24-29, 1987 ASTROPHYSICS Edited by PETR HARMANEC Proceedings, Vol. 1987 Publications of the Astronomical Institute of the Czechoslovak Academy of Sciences Publication No. 70 EUROPEAN REGIONAL ASTRONOMY MEETING OF THE I A U 10 Praha, Czechoslovakia August 24-29, 1987 ASTROPHYSICS Edited by PETR HARMANEC Proceedings, Vol. 5 1 987 CHIEF EDITOR OF THE PROCEEDINGS: LUBOS PEREK Astronomical Institute of the Czechoslovak Academy of Sciences 251 65 Ondrejov, Czechoslovakia TABLE OF CONTENTS Preface HI Invited discourse 3.-C. Pecker: Fran Tycho Brahe to Prague 1987: The Ever Changing Universe 3 lorlishdp on rapid variability of single, binary and Multiple stars A. Baglln: Time Scales and Physical Processes Involved (Review Paper) 13 Part 1 : Early-type stars P. Koubsfty: Evidence of Rapid Variability in Early-Type Stars (Review Paper) 25 NSV. Filtertdn, D.B. Gies, C.T. Bolton: The Incidence cf Absorption Line Profile Variability Among 33 the 0 Stars (Contributed Paper) R.K. Prinja, I.D. Howarth: Variability In the Stellar Wind of 68 Cygni - Not "Shells" or "Puffs", 39 but Streams (Contributed Paper) H. Hubert, B. Dagostlnoz, A.M. Hubert, M. Floquet: Short-Time Scale Variability In Some Be Stars 45 (Contributed Paper) G. talker, S. Yang, C. McDowall, G. Fahlman: Analysis of Nonradial Oscillations of Rapidly Rotating 49 Delta Scuti Stars (Contributed Paper) C. Sterken: The Variability of the Runaway Star S3 Arietis (Contributed Paper) S3 C. Blanco, A.
    [Show full text]
  • Searching for Strange Quark Matter Objects Among White Dwarfs
    Prepared for submission to JCAP Searching for Strange Quark Matter Objects Among White Dwarfs Abudushataer Kuerban,a;b Yong-Feng Huang,a;b;1 Jin-Jun Genga;b and Hong-Shi Zongc;d;e;f aSchool of Astronomy and Space Science, Nanjing University, Nanjing 210023, People’s Republic of China bKey Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, People’s Republic of China cDepartment of Physics, Nanjing University, Nanjing 210093, People’s Republic of China dJoint Center for Particle, Nuclear Physics and Cosmology, Nanjing 210093, People’s Republic of China eNanjing Institute of Proton Source Technology, Nanjing 210046, People’s Republic of China f Department of Physics, Anhui Normal University, Wuhu, Anhui 241000, People’s Republic of China E-mail: [email protected] Abstract. It has long been argued that the ground state of matter may be strange quark matter (SQM), not hadronic matter. A whole sequence of SQM objects, ranging from strange quark stars and strange quark dwarfs to strange quark planets, can stably exist according to this SQM hypothesis. A strange dwarf has a mass similar to that of a normal white dwarf, but could harbor an extremely dense SQM core (with the density as large as ∼ 4 × 1014 g cm−3) at the center so that its radius can be correspondingly smaller. In this study, we try to search for strange dwarfs among the observed “white dwarfs” by considering their difference in the mass-radius relation. Eight strange dwarf candidates are identified in this way, whose masses are in the range of ∼ 0:02M – 0:12M , with the radii narrowly distributed in ∼ 9,000 km – 15,000 km.
    [Show full text]
  • Some Interesting Twists in the Pulsating Sdb Star Puzzle
    Mem. S.A.It. Vol. 77, 402 c SAIt 2006 Memorie della Some interesting twists in the pulsating sdB star puzzle Steven D. Kawaler Department of Physics and Astronomy Iowa State University Ames, IA 50011 USA e-mail: [email protected] Abstract. In investigating the pulsation spectrum of the sdBV star PG 0014+067, we found a peculiar regularity of the pulsation frequencies reminiscent of asymptotic p−mode pulsa- tion along with rotational splitting. We have found a similar pattern in all other pulsating sdBV stars with multisite coverage. High-order p−mode pulsations (such as seen in the Sun and roAp stars) should not be present if our models of these stars and their pulsations are any guide to reality. The reasons for this pattern are currently unkonwn. Key words. Stars: pulsation – Stars: evolution – Stars: subdwarf B 1. Introduction Unfortunately, the models demand that these stars are showing low-order p−mode pulsa- The pulsation frequencies seen in pulsating tions, which show no such asymptotic patterns. subdwarf (sdBV) stars show frequencies that are of the same order as the radial fundamen- tal period. However, these stars generally show 2. PG 0014 Frequencies multiperiodic pulsation, with many modes pre- senting over a relatively narrow frequency The results of the WET run on PG 0014 will range. The reason for this rich mode spec- appear elsewhere (Vuckoviˇ c´ et al, in prepara- trum is unclear – proposed explanations range tion) but Table 1 presents our preliminary fre- from invoking nonradial modes with degree l quency list, merged with the frequencies found ranging from 0 to 3 or 4, to rotational split- by Jeffery et al.
    [Show full text]
  • Are Pulsars Bare Strange Stars?
    Pulsar Astronomy — 2000 and Beyond ASP Conference Series, Vol. 202, 2000 M. Kramer, N. Wex, and R. Wielebinski, eds. Are Pulsars Bare Strange Stars? R. X. Xu, G. J. Qiao, and B. Zhang CAS-PKU joint Beijing Astrophysical Center and Department of Astronomy, Peking University, Beijing 100781, China Abstract. It is believed that pulsars are neutron stars or strange stars with crusts. However we suggest here that pulsars may be bare strange stars (i.e., strange stars without crust). Due to rapid rotation and strong emission, young strange stars produced in supernova explosions should be bare when they act as radio pulsars. Because of strong magnetic field, two polar-crusts would shield the polar caps of an accreting strange star. Such a suggestion can be checked by further observations. Two greatest theories (i.e., gravity and quantum) developed in this century resulted in the formation of the theory of compact stars. One of such kind of stars observed are pulsars that were discovered by radio astronomers in 1960s. More observations later in X-ray and 7~ray bands confirmed the existence of pulsars in the nature: a kind of celestial bodies with masses ~ IMQ, radius ~ 10 km, and magnetic fields ~ 1012 gausses. Such objects, named as pulsars, are popularly thought to be neutron stars soon after the discoveries. Owing to the development of the hadronic quark model in 1960s and 1970s, it is conjectured that strange quark matter (SQM), composed of nearly equal numbers of up, down, and strange quarks, may be an absolutely stable 'hadron' of strong interaction confined states.
    [Show full text]
  • QUARK NUGGETS, DARK MATTER and PULSAR GLITCHES. Jes
    119 QUARK NUGGETS, DARK MATTER AND PULSAR GLITCHES. Jes Madsen Institute of Astronomy University of Aarhus DK-8000 Aarhus C, Denmark. ABSTRACT Very tight constraints are put oµ the occurrence of stable lumps of quark matter (quark nuggets) in our Galaxy. Only nuggets heavier than 1015 grammes remain possible candidates for the dark matter. A suggestion for solving the solar neutrino problem is ruled out, and some restrictions are set on models try­ ing to explain Centauro cosmic ray primaries or cygnets as quark nuggets. The existence of strange stars in binaries is questioned. The conclusions come from assuming that pulsar glitches can occur only in neutron stars, not in strange stars. As a consequence not a single quark nugget can have penetrated to the neutron drip region in a pulsar, and no quark nuggets can have been caught by the pulsar progenitor, since then the pulsar would have been converted to a strange star. This leads to limits on the galactic flux of quark nuggets many orders of magnitude better than limits from Earth-based detectors. The presen­ tation is based on a recent publication20>, but unpublished results on the fate of nuggets during supernova explosions and during collisions with neutron stars are included as well. 120 PHYSICS AND ASTROPHYSICS OF QUARK NUGGETS Quark matter composed of up, down and strange quarks in roughly equal propor­ tions (strangeI. matter) could be stable in bulk (i.e. stronger bound than 56Fe) at zero temperature and pressure for significant ranges of strong interaction parameters and strange quark masses.28L12l Quark nuggets (lumps of strange matter) could be the most bound state of baryonic matter for baryon number in the range A 10-100S A •10s1.
    [Show full text]
  • Structure of Quark Stars
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by El Servicio de Difusión de la Creación Intelectual Neutron Stars and Pulsars: Challenges and Opportunities after 80 years Proceedings IAU Symposium No. 291, 2012 °c International Astronomical Union 2013 J. van Leeuwen, ed. doi:10.1017/S1743921312023174 Structure of Quark Stars Fridolin Weber1, Milva Orsaria2, Hilario Rodrigues3 and Shu-Hua Yang4 1 Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA email: [email protected] 2 CONICET, Rivadavia 1917, 1033 Buenos Aires; Gravitation, Astrophysics and Cosmology Group, Facultad de Ciencias Astron´omicas y Geofisicas, Paseo del Bosque S/N (1900), Universidad Nacional de La Plata UNLP, La Plata, Argentina email: [email protected] 3 Centro Federal de Educa¸c˜ao Tecnol´ogica do Rio de Janeiro, Av Maracan˜a 249, 20271-110, Rio de Janeiro, RJ, Brazil email: [email protected] 4 Institute of Astrophysics, Huazhong Normal University, Wuhan, 430079, P. R. China email: [email protected] Abstract. This paper gives an brief overview of the structure of hypothetical strange quarks stars (quark stars, for short), which are made of absolutely stable 3-flavor strange quark matter. Such objects can be either bare or enveloped in thin nuclear crusts, which consist of heavy ions immersed in an electron gas. In contrast to neutron stars, the structure of quark stars is determined by two (rather than one) parameters, the central star density and the density at the base of the crust.
    [Show full text]
  • Magnetars Or Quark Stars?
    A&A manuscript no. (will be inserted by hand later) Your thesaurus codes are: 06; 19.63.1 Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars: Magnetars or Quark Stars? Arnon Dar1 and A. De R´ujula2 1. Department of Physics, Technion, Haifa 32000, Israel 2. Theory Division, CERN, CH-1211 Geneva 23, Switzerland the date of receipt and acceptance should be inserted later Abstract. Recent measurements of the spin-down rates of soft gamma ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) have been interpreted as evidence that these objects are “magnetars”: neutron stars spinning down by magnetic dipole radiation, but with a magnetic field two orders of magnitude larger than that of ordinary neutron stars. We discuss the evidence disfavouring this interpretation. We argue that, instead, the observations support the hypothesis that SGRs and AXPs are neutron stars that have suffered a transition into a denser form of nuclear matter to become, presumably, strange stars or quark stars. 1. Introduction Consider a neutron star (NS) of radius R, with a magnetic field Bp at the magnetic poles, spinning with a period P. If the star’s magnetic moment is misaligned with the spin axis by an angle α, electromagnetic energy is emitted at a rate (see, e.g., Shapiro & Teukolsky 1983 and references therein.) 2 6 4 2 Bp R Ω sin α E=˙ − , (1) 6c3 with Ω = 2π/P the angular velocity. If the NS is observed as a pulsar, its period can be measured as a function of time. Let the NS have a moment of inertia I and let Pbethe˙ rate at which its period decreases.
    [Show full text]
  • Are Pulsars Bare Strange Stars?
    Are Pulsars Bare Strange Stars? R.X. Xu, G.J. Qiao, B. Zhang CAS-PKU joint Beijing Astrophysical Center and Department of Astronomy, Peking University, Beijing 100781, China Presented in IAU Colloquium 177: Pulsar Astronomy and Beyond August 30 – Setpember 3, 1999, Bonn, Germany Abstract It is believed that pulsars are neutron stars or strange stars with crusts. However we suggest here that pulsars may be bare strange stars (i.e., strange stars without crust). Due to rapid rotation and strong emission, young strange stars produced in supernova explosions should be bare when they act as radio pulsars. Because of strong magnetic field, two polar-crusts would shield the polar caps of an accreting strange star. Such a suggestion can be checked by further observations. Two greatest theories (i.e., gravity and quantum) developed in this century resulted in the formation of the theory of compact stars. One of such kind of stars observed are pulsars that were discovered by radio astronomers in 1960s. More observations later in X-ray and γ-ray bands confirmed the existence of pulsars in the nature: a 12 kind of celestial bodies with masses ∼ 1M⊙, radius ∼ 10 km, and magnetic fields ∼ 10 gausses. Such objects, named as pulsars, are popularly thought to be neutron stars soon after the discoveries. Owing to the development of the hadronic quark model in 1960s and 1970s, it is conjectured that strange quark matter (SQM), composed of nearly equal numbers of up, down, and strange quarks, may be an absolutely stable ‘hadron’ of strong interaction confined states. If this assumption is true, strange star1 is in the nature, which should be a ground state of neutron star.
    [Show full text]