DOCSLIB.ORG

Neutron Star Collapse Times, Gamma-Ray Bursts and Fast Radio Bursts

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Neutron Star Collapse Times, Gamma-Ray Bursts and Fast Radio Bursts MNRAS 441, 2433–2439 (2014) doi:10.1093/mnras/stu720 The birth of black holes: neutron star collapse times, gamma-ray bursts and fast radio bursts ‹ Vikram Ravi1,2 and Paul D. Lasky1 Downloaded from https://academic.oup.com/mnras/article-abstract/441/3/2433/1126394 by California Institute of Technology user on 24 June 2019 1School of Physics, University of Melbourne, Parkville, VIC 3010, Australia 2CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia Accepted 2014 April 8. Received 2014 April 7; in original form 2013 November 29 ABSTRACT Recent observations of short gamma-ray bursts (SGRBs) suggest that binary neutron star (NS) mergers can create highly magnetized, millisecond NSs. Sharp cut-offs in X-ray afterglow plateaus of some SGRBs hint at the gravitational collapse of these remnant NSs to black holes. The collapse of such ‘supramassive’ NSs also describes the blitzar model, a leading candidate for the progenitors of fast radio bursts (FRBs). The observation of an FRB associated with an SGRB would provide compelling evidence for the blitzar model and the binary NS merger scenario of SGRBs, and lead to interesting constraints on the NS equation of state. We predict the collapse times of supramassive NSs created in binary NS mergers, finding that such stars collapse ∼10–4.4 × 104 s (95 per cent confidence) after the merger. This directly impacts observations targeting NS remnants of binary NS mergers, providing the optimal window for high time resolution radio and X-ray follow-up of SGRBs and gravitational wave bursts. Key words: black hole physics – equation of state – gamma-ray burst: general – stars: magne- tars – radio continuum: general. the resulting outwardly propagating magnetic shock dissipates as 1 INTRODUCTION a short, intense radio burst (Dionysopoulou et al. 2013; Falcke & Fast radio bursts (FRBs; Lorimer et al. 2007; Keane et al. 2012; Rezzolla 2014). Thornton et al. 2013) are among the most exciting astronomical dis- The merger of two NSs is one possible formation channel for coveries of the last decade. They are intense, millisecond-duration supramassive NSs. In general, there are three possible outcomes broad-band bursts of radio waves so far detected in the 1.2–1.6 GHz of such a merger, which, for a given NS equation of state (EOS), −3 band, with dispersion measures between 300 and 1200 cm pc. depend on the nascent NS mass, Mp, and angular momentum dis- FRBs are not associated with any known astrophysical object. Their tribution. These outcomes are as follows. anomalously large dispersion measures, given their high Galactic (i) If M ≤ M ,whereM is the maximum non-rotating latitudes, combined with the observed effects of scattering consis- p TOV TOV mass, the NS will settle to an equilibrium state that is uniformly tent with propagation through a large ionized volume (Lorimer et al. rotating and eternally stable (e.g. Giacomazzo & Perna 2013). 2007; Thornton et al. 2013), suggest a cosmological origin for FRBs (ii) If M > M , and if magnetic braking has caused the star (although see Burke-Spolaor et al. 2011; Bannister & Madsen 2014; p TOV to rotate uniformly (see below), it will survive for 1 s as a supra- Loeb, Shvartzvald & Maoz 2014). massive star until centrifugal support is reduced to the point where Numerous physical mechanisms have been suggested to produce the star collapses to a black hole (e.g. Duez et al. 2006). FRBs at cosmological distances, including magnetar hyperflares (iii) If M is greater than the maximum mass that may be sup- (e.g. Popov & Postnov 2013), binary white dwarf (Kashiyama, Ioka p ported by uniform rotation, the NS may either instantly collapse to &Mesz´ aros´ 2013)orneutronstar(NS;Totani2013) mergers, and a black hole or survive for 10−100 ms as a hypermassive star sup- the collapse of supramassive NSs to form black holes (Falcke & ported by differential rotation and thermal pressures (e.g. Baiotti, Rezzolla 2014). Here, we focus on the latter mechanism, termed Giacomazzo & Rezzolla 2008;Kiuchietal.2009; Rezzolla et al. the ‘blitzar’ model. A supramassive NS is one that has a mass 2011; Hotokezaka et al. 2013). greater than the non-rotating maximum mass, but is supported from collapse by rotation. As these stars spin down, they lose centrifugal Gamma-ray bursts (GRBs) with short durations (2 s) and hard support and eventually collapse to black holes. When magnetic spectra are associated with the coalescences of compact object bina- field lines cross the newly formed horizon, they snap violently, and ries, i.e. either NS–NS or NS–black hole mergers (Lee & Ramirez- Ruiz 2007; Nakar 2007;Berger2013). However, the emission mech- anisms of short GRBs (SGRBs) are not well understood. From E-mail: [email protected] a theoretical standpoint, a short-lived, collimated, relativistic jet C 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society 2434 V. Ravi and P. D. Lasky can be launched from both black hole (e.g. Rezzolla et al. 2011) decline in the plateau phase of an SGRB X-ray light curve would and NS (e.g. Metzger, Quataert & Thompson 2008) remnants of provide powerful evidence for the protomagnetar model for SGRBs, compact binary coalescences, as necessitated by the ‘relativistic as well as the blitzar model of FRBs. FRB/SGRB associations may fireball’ model of prompt GRB emission (e.g. Piran 1999;Lee& also be used to characterize the intergalactic baryon content of the Ramirez-Ruiz 2007; Nakar 2007). Jet launching through magnetic Universe (Deng & Zhang 2014) through measurements of FRB dis- acceleration requires a short-lived (∼0.1–1 s) accretion disc, and persion measures and SGRB redshifts. Our results also provide a toroidal and small-opening-angle poloidal magnetic fields that are quantitative guide to interpreting observations of declines in SGRB Downloaded from https://academic.oup.com/mnras/article-abstract/441/3/2433/1126394 by California Institute of Technology user on 24 June 2019 both ∼1015 G (e.g. Komissarov et al. 2009). Numerical simulations X-ray light curves (Rowlinson et al. 2013) in the context of supra- of the merger of two 1.5 M NSs with 1012 G poloidal magnetic massive protomagnetar collapse. In particular, secure measurements fields (Rezzolla et al. 2011) result in a black hole remnant with the of the lifetimes of supramassive NSs produced in binary NS merg- necessary conditions, where the magnetic field is amplified through ers allow for interesting new constraints to be placed on the EOS of magnetohydrodynamic instabilities, to launch a jet with an energy nuclear matter (Lasky et al. 2014). output of ∼1.2 × 1051 erg. This is consistent with SGRB observa- Mergers of binary NSs are prime candidate sources for ground- tions (Lee & Ramirez-Ruiz 2007; Nakar 2007). Simulations of a based gravitational wave (GW) interferometers (Abadie et al. 2010). lower mass NS binary coalescence by Giacomazzo & Perna (2013) However, the collimated nature of SGRBs (e.g. Burrows et al. 2006) resulted in a stable millisecond ‘protomagnetar’, although the small- implies not all GW events will be associated with SGRBs. Some scale instabilities required to amplify the magnetic field to ∼1015 G alternative EM signals of GW bursts (Gao et al. 2013; Zhang 2013) were unresolved. On the other hand, high-resolution simulations rely on the births of stable or supramassive NSs acting as central of isolated NSs (e.g. Duez et al. 2006) show that magnetic field engines, implying that the time-scales for these signals are sensi- amplification to ∼1015 G and accretion disc formation is possi- tively related to the lifetimes of the nascent NSs and therefore the ble for nascent protomagnetars, suggesting that protomagnetars can calculations performed herein. power prompt SGRB emission through magnetically accelerated We show that, if a binary NS merger remnant does not collapse jets. Baryon-free energy deposition through neutrino–antineutrino in the first ∼4.4 × 104 s after formation, it is unlikely to collapse annihilation, driven by accretion on to protomagnetars, is another at all (97.5 per cent confidence). That is, almost all supramassive mechanism to power prompt SGRBs (Metzger et al. 2008). In this NSs born from binary NS mergers will collapse to form black holes paper, we assume that nascent protomagnetars formed through bi- within ∼4.4 × 104 s. In Section 2, we summarize our method for nary NS coalescences can power prompt SGRB emission, although calculating the range of collapse times of merger remnants. We we note that a deeper understanding is still required. check the consistency of this method against a sample of SGRBs The most attractive characteristic of the protomagnetar model for with X-ray plateaus from Rowlinson et al. (2013) in Section 3. SGRBs is its ability to explain features of the X-ray afterglows (Gao In Section 4, we generalize our calculations to the full population &Fan2006; Metzger et al. 2008). Lasting a few hundred seconds of binary NS merger remnants, and we present our conclusions in following the initial burst, these features are either extremely bright Section 5. (up to 30 times the fluence of the prompt emission; Perley et al. 2009) and variable on time-scales comparable to prompt emission 2 PREDICTING SUPRAMASSIVE NEUTRON variability, or smoothly decaying plateaus (Rowlinson et al. 2013). STAR COLLAPSE TIMES Both features are difficult to explain through, for example, fall-back accretion on to black hole central engines (Metzger et al. 2008;Buc- The problem of identifying the spin-down torques on nascent NSs ciantini et al. 2012, and references therein), although see Siegel, has been extensively studied over the last 50 years, with the pri- Ciolfi & Rezzolla (2014).
Load more

Recommended publications
  • White Dwarfs
    Chandra X-Ray Observatory X-Ray Astronomy Field Guide White Dwarfs White dwarfs are among the dimmest stars in the universe. Even so, they have commanded the attention of astronomers ever since the first white dwarf was observed by optical telescopes in the middle of the 19th century. One reason for this interest is that white dwarfs represent an intriguing state of matter; another reason is that most stars, including our sun, will become white dwarfs when they reach their final, burnt-out collapsed state. A star experiences an energy crisis and its core collapses when the star's basic, non-renewable energy source - hydrogen - is used up. A shell of hydrogen on the edge of the collapsed core will be compressed and heated. The nuclear fusion of the hydrogen in the shell will produce a new surge of power that will cause the outer layers of the star to expand until it has a diameter a hundred times its present value. This is called the "red giant" phase of a star's existence. A hundred million years after the red giant phase all of the star's available energy resources will be used up. The exhausted red giant will puff off its outer layer leaving behind a hot core. This hot core is called a Wolf-Rayet type star after the astronomers who first identified these objects. This star has a surface temperature of about 50,000 degrees Celsius and is A composite furiously boiling off its outer layers in a "fast" wind traveling 6 million image of the kilometers per hour.
    [Show full text]
  • Pdf/44/4/905/5386708/44-4-905.Pdf
    MI-TH-214 INT-PUB-21-004 Axions: From Magnetars and Neutron Star Mergers to Beam Dumps and BECs Jean-François Fortin∗ Département de Physique, de Génie Physique et d’Optique, Université Laval, Québec, QC G1V 0A6, Canada Huai-Ke Guoy and Kuver Sinhaz Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA Steven P. Harrisx Institute for Nuclear Theory, University of Washington, Seattle, WA 98195, USA Doojin Kim{ Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA Chen Sun∗∗ School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978, Israel (Dated: February 26, 2021) We review topics in searches for axion-like-particles (ALPs), covering material that is complemen- tary to other recent reviews. The first half of our review covers ALPs in the extreme environments of neutron star cores, the magnetospheres of highly magnetized neutron stars (magnetars), and in neu- tron star mergers. The focus is on possible signals of ALPs in the photon spectrum of neutron stars and gravitational wave/electromagnetic signals from neutron star mergers. We then review recent developments in laboratory-produced ALP searches, focusing mainly on accelerator-based facilities including beam-dump type experiments and collider experiments. We provide a general-purpose discussion of the ALP search pipeline from production to detection, in steps, and our discussion is straightforwardly applicable to most beam-dump type and reactor experiments. We end with a selective look at the rapidly developing field of ultralight dark matter, specifically the formation of Bose-Einstein Condensates (BECs).
    [Show full text]
  • Magnetars: Explosive Neutron Stars with Extreme Magnetic Fields
    Magnetars: explosive neutron stars with extreme magnetic fields Nanda Rea Institute of Space Sciences, CSIC-IEEC, Barcelona 1 How magnetars are discovered? Soft Gamma Repeaters Bright X-ray pulsars with 0.5-10keV spectra modelled by a thermal plus a non-thermal component Anomalous X-ray Pulsars Bright X-ray transients! Transients No more distinction between Anomalous X-ray Pulsars, Soft Gamma Repeaters, and transient magnetars: all showing all kind of magnetars-like activity. Nanda Rea CSIC-IEEC Magnetars general properties 33 36 Swift-XRT COMPTEL • X-ray pulsars Lx ~ 10 -10 erg/s INTEGRAL • strong soft and hard X-ray emission Fermi-LAT • short X/gamma-ray flares and long outbursts (Kuiper et al. 2004; Abdo et al. 2010) • pulsed fractions ranging from ~2-80 % • rotating with periods of ~0.3-12s • period derivatives of ~10-14-10-11 s/s • magnetic fields of ~1013-1015 Gauss (Israel et al. 2010) • glitches and timing noise (Camilo et al. 2006) • faint infrared/optical emission (K~20; sometimes pulsed and transient) • transient radio pulsed emission (see Woods & Thompson 2006, Mereghetti 2008, Rea & Esposito 2011 for a review) Nanda Rea CSIC-IEEC How magnetar persistent emission is believed to work? • Magnetars have magnetic fields twisted up, inside and outside the star. • The surface of a young magnetar is so hot that it glows brightly in X-rays. • Magnetar magnetospheres are filled by charged particles trapped in the twisted field lines, interacting with the surface thermal emission through resonant cyclotron scattering. (Thompson, Lyutikov & Kulkarni 2002; Fernandez & Thompson 2008; Nobili, Turolla & Zane 2008a,b; Rea et al.
    [Show full text]
  • Pos(INTEGRAL 2010)091
    A candidate former companion star to the Magnetar CXOU J164710.2-455216 in the massive Galactic cluster Westerlund 1 PoS(INTEGRAL 2010)091 P.J. Kavanagh 1 School of Physical Sciences and NCPST, Dublin City University Glasnevin, Dublin 9, Ireland E-mail: [email protected] E.J.A. Meurs School of Cosmic Physics, DIAS, and School of Physical Sciences, DCU Glasnevin, Dublin 9, Ireland E-mail: [email protected] L. Norci School of Physical Sciences and NCPST, Dublin City University Glasnevin, Dublin 9, Ireland E-mail: [email protected] Besides carrying the distinction of being the most massive young star cluster in our Galaxy, Westerlund 1 contains the notable Magnetar CXOU J164710.2-455216. While this is the only collapsed stellar remnant known for this cluster, a further ~10² Supernovae may have occurred on the basis of the cluster Initial Mass Function, possibly all leaving Black Holes. We identify a candidate former companion to the Magnetar in view of its high proper motion directed away from the Magnetar region, viz. the Luminous Blue Variable W243. We discuss the properties of W243 and how they pertain to the former Magnetar companion hypothesis. Binary evolution arguments are employed to derive a progenitor mass for the Magnetar of 24-25 M Sun , just within the progenitor mass range for Neutron Star birth. We also draw attention to another candidate to be member of a former massive binary. 8th INTEGRAL Workshop “The Restless Gamma-ray Universe” Dublin, Ireland September 27-30, 2010 1 Speaker Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
    [Show full text]
  • Rotating Stars in Relativity
    Noname manuscript No. (will be inserted by the editor) Rotating Stars in Relativity Vasileios Paschalidis Nikolaos Stergioulas · Received: date / Accepted: date Abstract Rotating relativistic stars have been studied extensively in recent years, both theoretically and observationally, because of the information they might yield about the equation of state of matter at extremely high densi- ties and because they are considered to be promising sources of gravitational waves. The latest theoretical understanding of rotating stars in relativity is re- viewed in this updated article. The sections on equilibrium properties and on nonaxisymmetric oscillations and instabilities in f-modes and r-modes have been updated. Several new sections have been added on equilibria in modi- fied theories of gravity, approximate universal relationships, the one-arm spiral instability, on analytic solutions for the exterior spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating stars in numerical relativ- ity including both hydrodynamic and magnetohydrodynamic studies of these objects. Keywords Relativistic stars · Rotation · Stability · Oscillations · Magnetic fields · Numerical relativity Vasileios Paschalidis Theoretical Astrophysics Program, Departments of Astronomy and Physics, University of Arizona, Tucson, AZ 85721, USA Department of Physics, Princeton University Princeton, NJ 08544, USA E-mail: [email protected] http://physics.princeton.edu/~vp16/ Nikolaos Stergioulas Department of Physics, Aristotle University of Thessaloniki Thessaloniki, 54124, Greece E-mail: [email protected] http://www.astro.auth.gr/~niksterg arXiv:1612.03050v2 [astro-ph.HE] 30 Nov 2017 2 Vasileios Paschalidis, Nikolaos Stergioulas The article has been substantially revised and updated. New Section 5 and various Subsections (2.3 { 2.5, 2.7.5 { 2.7.7, 2.8, 2.10-2.11,4.5.7) have been added.
    [Show full text]
  • Supernovae Sparked by Dark Matter in White Dwarfs
    Supernovae Sparked By Dark Matter in White Dwarfs Javier F. Acevedog and Joseph Bramanteg;y gThe Arthur B. McDonald Canadian Astroparticle Physics Research Institute, Department of Physics, Engineering Physics, and Astronomy, Queen's University, Kingston, Ontario, K7L 2S8, Canada yPerimeter Institute for Theoretical Physics, Waterloo, Ontario, N2L 2Y5, Canada November 27, 2019 Abstract It was recently demonstrated that asymmetric dark matter can ignite supernovae by collecting and collapsing inside lone sub-Chandrasekhar mass white dwarfs, and that this may be the cause of Type Ia supernovae. A ball of asymmetric dark matter accumulated inside a white dwarf and collapsing under its own weight, sheds enough gravitational potential energy through scattering with nuclei, to spark the fusion reactions that precede a Type Ia supernova explosion. In this article we elaborate on this mechanism and use it to place new bounds on interactions between nucleons 6 16 and asymmetric dark matter for masses mX = 10 − 10 GeV. Interestingly, we find that for dark matter more massive than 1011 GeV, Type Ia supernova ignition can proceed through the Hawking evaporation of a small black hole formed by the collapsed dark matter. We also identify how a cold white dwarf's Coulomb crystal structure substantially suppresses dark matter-nuclear scattering at low momentum transfers, which is crucial for calculating the time it takes dark matter to form a black hole. Higgs and vector portal dark matter models that ignite Type Ia supernovae are explored. arXiv:1904.11993v3 [hep-ph] 26 Nov 2019 Contents 1 Introduction 2 2 Dark matter capture, thermalization and collapse in white dwarfs 4 2.1 Dark matter capture .
    [Show full text]
  • The Impact of the Astro2010 Recommendations on Variable Star Science
    The Impact of the Astro2010 Recommendations on Variable Star Science Corresponding Authors Lucianne M. Walkowicz Department of Astronomy, University of California Berkeley [email protected] phone: (510) 642–6931 Andrew C. Becker Department of Astronomy, University of Washington [email protected] phone: (206) 685–0542 Authors Scott F. Anderson, Department of Astronomy, University of Washington Joshua S. Bloom, Department of Astronomy, University of California Berkeley Leonid Georgiev, Universidad Autonoma de Mexico Josh Grindlay, Harvard–Smithsonian Center for Astrophysics Steve Howell, National Optical Astronomy Observatory Knox Long, Space Telescope Science Institute Anjum Mukadam, Department of Astronomy, University of Washington Andrej Prsa,ˇ Villanova University Joshua Pepper, Villanova University Arne Rau, California Institute of Technology Branimir Sesar, Department of Astronomy, University of Washington Nicole Silvestri, Department of Astronomy, University of Washington Nathan Smith, Department of Astronomy, University of California Berkeley Keivan Stassun, Vanderbilt University Paula Szkody, Department of Astronomy, University of Washington Science Frontier Panels: Stars and Stellar Evolution (SSE) February 16, 2009 Abstract The next decade of survey astronomy has the potential to transform our knowledge of variable stars. Stellar variability underpins our knowledge of the cosmological distance ladder, and provides direct tests of stellar formation and evolution theory. Variable stars can also be used to probe the fundamental physics of gravity and degenerate material in ways that are otherwise impossible in the laboratory. The computational and engineering advances of the past decade have made large–scale, time–domain surveys an immediate reality. Some surveys proposed for the next decade promise to gather more data than in the prior cumulative history of astronomy.
    [Show full text]
  • Radio Observations of the Supermassive Black Hole at the Galactic Center and Its Orbiting Magnetar
    Radio Observations of the Supermassive Black Hole at the Galactic Center and its Orbiting Magnetar Rebecca Rimai Diesing Honors Thesis Department of Physics and Astronomy Northwestern University Spring 2017 Honors Thesis Advisor: Farhad Zadeh ! Radio Observations of the Supermassive Black Hole at the Galactic Center and its Orbiting Magnetar Rebecca Rimai Diesing Department of Physics and Astronomy Northwestern University Honors Thesis Advisor: Farhad Zadeh Department of Physics and Astronomy Northwestern University At the center of our galaxy a bright radio source, Sgr A*, coincides with a black hole four million times the mass of our sun. Orbiting Sgr A* at a distance of 3 arc seconds (an estimated 0.1 pc) and rotating with a period of 3.76 s is a magnetar, or pulsar⇠ with an extremely strong magnetic field. This magnetar exhibited an X-ray outburst in April 2013, with enhanced, highly variable radio emission detected 10 months later. In order to better understand the behavior of Sgr A* and the magnetar, we study their intensity variability as a function of both time and frequency. More specifically, we present the results of short (8 minute) and long (7 hour) radio continuum observations, taken using the Jansky Very Large Array (VLA) over multiple epochs during the summer of 2016. We find that Sgr A*’s flux density (a proxy for intensity) is highly variable on an hourly timescale, with a frequency dependence that di↵ers at low (34 GHz) and high (44 GHz) frequencies. We also find that the magnetar remains highly variable on both short (8 min) and long (monthly) timescales, in agreement with observations from 2014.
    [Show full text]
  • A Hidden Population of Exotic Neutron Stars 23 May 2013
    A hidden population of exotic neutron stars 23 May 2013 times stronger than for the average neutron star. New observations show that the magnetar known as SGR 0418+5729 (SGR 0418 for short) doesn't fit that pattern. It has a surface magnetic field similar to that of mainstream neutron stars. "We have found that SGR 0418 has a much lower surface magnetic field than any other magnetar," said Nanda Rea of the Institute of Space Science in Barcelona, Spain. "This has important consequences for how we think neutron stars evolve in time, and for our understanding of Credit: X-ray: NASA/CXC/CSIC-IEEC/N.Rea et al; supernova explosions." Optical: Isaac Newton Group of Telescopes, La Palma/WHT; Infrared: NASA/JPL-Caltech; Illustration: The researchers monitored SGR 0418 for over NASA/CXC/M.Weiss three years using Chandra, ESA's XMM-Newton as well as NASA's Swift and RXTE satellites. They were able to make an accurate estimate of the strength of the external magnetic field by (Phys.org) —Magnetars – the dense remains of measuring how its rotation speed changes during dead stars that erupt sporadically with bursts of an X-ray outburst. These outbursts are likely high-energy radiation - are some of the most caused by fractures in the crust of the neutron star extreme objects known in the Universe. A major precipitated by the buildup of stress in a relatively campaign using NASA's Chandra X-ray strong, wound-up magnetic field lurking just Observatory and several other satellites shows beneath the surface. magnetars may be more diverse - and common - than previously thought.
    [Show full text]
  • Neutron Stars: End State of High-Mass Stars
    Chapter 13: The Stellar Graveyard 3/31/2009 Habbal Astro110http://chandra.harvard.edu/photo/2001/1227/index.html Chapter 13 Lecture 26 1 Low mass star High mass (>8 Msun) star Ends as a white dwarf. Ends in a supernova, leaving a neutron star or black hole 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 2 White dwarfs: end state of low-mass stars • Inert remaining cores of dead low-mass stars. • No internal energy generation: start hot and steadily cool off. Optical image X-ray image Sirius A Sirius A high mass star high mass star Sirius B Sirius B white dwarf white dwarf 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 3 White dwarfs are supported against gravitational collapse by electron degeneracy pressure 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 4 A 1 MSun white dwarf is about the same size as the Earth… ⇒ A teaspoon of white dwarf material would weight 10 tons! 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 5 More massive white dwarfs are smaller! Mass ⇒ gravitational compression ⇒ density ⇒ radius Chandrasekhar limit: white dwarfs cannot be more massive than 1.4 MSun 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 6 White dwarfs in binary systems • WDʼs gravity can accrete gas from companion star. • Accreted gas can erupt in a short modest burst of nuclear fusion: novae • However, WDs cannot BANG! be more than 1.4 MSun. • If WD accretes too much gas, it is destroyed in a white dwarf supernova 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 7 Nova: a nuclear explosion on the surface of a WD, gas is expelled and system returns to normal 3/31/2009 Habbal Astro110 Chapter 13 Lecture 26 8 One way to tell supernova types apart is with a light curve showing how the luminosity changes.
    [Show full text]
  • Stellar Death: White Dwarfs, Neutron Stars, and Black Holes
    Stellar death: White dwarfs, Neutron stars & Black Holes Content Expectaions What happens when fusion stops? Stars are in balance (hydrostatic equilibrium) by radiation pushing outwards and gravity pulling in What will happen once fusion stops? The core of the star collapses spectacularly, leaving behind a dead star (compact object) What is left depends on the mass of the original star: <8 M⦿: white dwarf 8 M⦿ < M < 20 M⦿: neutron star > 20 M⦿: black hole Forming a white dwarf Powerful wind pushes ejects outer layers of star forming a planetary nebula, and exposing the small, dense core (white dwarf) The core is about the radius of Earth Very hot when formed, but no source of energy – will slowly fade away Prevented from collapsing by degenerate electron gas (stiff as a solid) Planetary nebulae (nothing to do with planets!) THE RING NEBULA Planetary nebulae (nothing to do with planets!) THE CAT’S EYE NEBULA Death of massive stars When the core of a massive star collapses, it can overcome electron degeneracy Huge amount of energy BAADE ZWICKY released - big supernova explosion Neutron star: collapse halted by neutron degeneracy (1934: Baade & Zwicky) Black Hole: star so massive, collapse cannot be halted SN1006 1967: Pulsars discovered! Jocelyn Bell and her supervisor Antony Hewish studying radio signals from quasars Discovered recurrent signal every 1.337 seconds! Nicknamed LGM-1 now called PSR B1919+21 BRIGHTNESS TIME NATURE, FEBRUARY 1968 1967: Pulsars discovered! Beams of radiation from spinning neutron star Like a lighthouse Neutron
    [Show full text]
  • One Or Several Populations of Fast Radio Burst Sources?
    One or several populations of fast radio burst sources? M. Caleb1, L. G. Spitler2 & B. W. Stappers1 1Jodrell Bank Centre for Astrophysics, the University of Manchester, Manchester, UK. 2Max-Planck-Institut fu¨r Radioastronomie, Bonn, Germany. arXiv:1811.00360v1 [astro-ph.HE] 1 Nov 2018 1 To date, one repeating and many apparently non-repeating fast radio bursts have been de- tected. This dichotomy has driven discussions about whether fast radio bursts stem from a single population of sources or two or more different populations. Here we present the arguments for and against. The field of fast radio bursts (FRBs) has increasingly gained momentum over the last decade. Overall, the FRBs discovered to date show a remarkable diversity of observed properties (see ref 1, http://frbcat.org and Fig. 1). Intrinsic properties that tell us something about the source itself, such as polarization and burst profile shape, as well as extrinsic properties that tell us something about the source’s environment, such as the magnitude of Faraday rotation and multi-path propagation effects, do not yet present a coherent picture. Perhaps the most striking difference is between FRB 121102, the sole repeating FRB2, and the more than 60 FRBs that have so far not been seen to repeat. The observed dichotomy suggests that we should consider the existence of multiple source populations, but it does not yet require it. Most FRBs to date have been discovered with single-pixel telescopes with relatively large angular resolutions. As a result, the non-repeating FRBs have typically been localized to no bet- ter than a few to tens of arcminutes on the sky (Fig.
    [Show full text]