Pulsar–black hole binaries in the Galactic Centre

Binaries consisting of a pulsar and a black hole (BH) are a holy grail of astrophysics, both for their significance for stellar evolution and for their potential application as probes of strong gravity. In spite of extensive surveys of our Galaxy and its system of globular clusters, no pulsar–black hole (PSR–BH) binary has been found to date. Clues as to where such systems might exist are therefore important. We show that if the central parsec around Sgr A★ harbours a cluster of ∼25 000 stellar BHs (as predicted by mass-segregation arguments) and if it is also rich in recycled pulsar binaries (by analogy with globular clusters), then three-body exchange interactions should produce PSR–BHs in the Galactic Centre. Simple estimates of the formation rate and survival time of these binaries suggest that a few PSR–BHs should be present in the central parsec today. The proposed formation mechanism makes unique predictions for the PSR–BH properties: (1) the binary would reside within ∼1 pc of Sgr A★; (2) the pulsar would be recycled, with a period of ∼1 to a few tens of milliseconds, and a low magnetic field B≲ 1010 G; (3) the binary would have high eccentricity, e∼ 0.8, but with a large scatter and (4) the binary would be relatively wide, with semimajor axis ab∼ 0.1 −≳3 au. The potential discovery of a PSR–BH binary therefore provides a strong motivation for deep, high-frequency radio searches for recycled pulsars towards the Galactic Centre.

[1]  D. Helfand,et al.  The Origin and Evolution of Neutron Stars , 1987 .

[2]  T. Piran,et al.  Neutron Star and Black Hole Binaries in the Galaxy , 1991 .

[3]  Andrew Gould,et al.  A Cluster of Black Holes at the Galactic Center , 2000, astro-ph/0003269.

[4]  R. Manchester,et al.  Spectra of southern pulsars , 1998, astro-ph/9805241.

[5]  S. Rappaport,et al.  Formation of Short-Period Binary Pulsars in Globular Clusters , 1999, The Astrophysical journal.

[6]  Karl Gebhardt,et al.  Gemini and Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in ω Centauri , 2008 .

[7]  Michael J. Kurtz,et al.  Hypervelocity Stars. III. The Space Density and Ejection History of Main-Sequence Stars from the Galactic Center , 2007, 0709.1471.

[8]  F. Verbunt.  The formation of ultra-short period binaries in globular clusters , 1987 .

[9]  Steinn Sigurdsson,et al.  Primordial black holes in globular clusters , 1993, Nature.

[10]  C. Bailyn,et al.  Hubble Space Telescope Observations of the Post-Core-Collapse Globular Cluster NGC 6752. II. A Large Main-Sequence Binary Population , 1997 .

[11]  Qingjuan Yu,et al.  Ejection of Hypervelocity Stars by the (Binary) Black Hole in the Galactic Center , 2003 .

[12]  Piet Hut,et al.  Stellar black holes in globular clusters , 1993, Nature.

[13]  M. Tavani.  'Hidden' millisecond pulsars , 1991 .

[14]  J. Chiang,et al.  A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope , 2010, 1003.3588.

[15]  A. Loeb,et al.  The fate of former companions to hypervelocity stars originating at the Galactic Centre , 2005, astro-ph/0510574.

[16]  W. B. Burton.  The Large-Scale Characteristics of the Galaxy , 1979 .

[17]  S. Sigurdsson,et al.  Nova Scorpii and Coalescing Low-Mass Black Hole Binaries as LIGO Sources , 2002, astro-ph/0202385.

[18]  Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16 , 2010, 1011.0718.

[19]  R. Wolf,et al.  Star distribution around a massive black hole in a globular cluster. II. Unequal star masses , 1977 .

[20]  A. Loeb,et al.  Probing the Spacetime around Sagittarius A* with Radio Pulsars , 2003, astro-ph/0309744.

[21]  I. Stairs.  Pulsars in Binary Systems: Probing Binary Stellar Evolution and General Relativity , 2004, Science.

[22]  H. Bethe,et al.  Contribution of High-Mass Black Holes to Mergers of Compact Binaries , 1998, astro-ph/9805355.

[23]  Clovis Hopman,et al.  The Effect of Mass Segregation on Gravitational Wave Sources near Massive Black Holes , 2006 .

[24]  J. Cordes,et al.  DISCOVERY OF THREE PULSARS FROM A GALACTIC CENTER PULSAR POPULATION , 2009, 0908.1331.

[25]  S. Shapiro,et al.  The distribution and consumption rate of stars around a massive, collapsed object , 1977 .

[26]  Karl Gebhardt,et al.  Evidence for an Intermediate Mass Black Hole in Omega Centauri , 2006, 0801.2782.

[27]  T. Paumard,et al.  AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS , 2009, 0908.2177.

[28]  D. Lorimer,et al.  Pulsar science with the Five hundred metre Aperture Spherical Telescope , 2009, 0908.1689.

[29]  Steinn Sigurdsson,et al.  MODELING THE RETENTION PROBABILITY OF BLACK HOLES IN GLOBULAR CLUSTERS: KICKS AND RATES , 2008, 0809.1617.

[30]  Philipp Podsiadlowski,et al.  Submitted to ApJ Preprint typeset using L ATEX style emulateapj v. 21/08/00 A COMPREHENSIVE STUDY OF NEUTRON STAR RETENTION IN GLOBULAR CLUSTERS , 2001 .

[31]  M. Kramer,et al.  Observations of pulsars at 9 millimetres , 2008, 0802.1339.

[32]  Jay Anderson,et al.  NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. II. DYNAMICAL MODELS , 2009, 0905.0638.

[33]  A. Eckart,et al.  Composition of the galactic center star cluster. Population analysis from adaptive optics narrow ban , 2009, 0903.2135.

[34]  Harvard University,et al.  Birth and Evolution of Isolated Radio Pulsars , 2005, astro-ph/0512585.

[35]  P. Hut.  Hard binary-single star scattering cross sections for equal masses , 1984 .

[36]  A. Eckart,et al.  The nuclear star cluster of the Milky Way: proper motions and mass , 2009, 0902.3892.

[37]  B. Hansen,et al.  Neutron star retention and millisecond pulsar production in globular clusters , 1998 .

[38]  A. Gould,et al.  Sagittarius A* Companion S0-2: A Probe of Very High Mass Star Formation , 2003, astro-ph/0302437.

[39]  W. M. Goss,et al.  A Radio Transient 0.1 Parsecs from Sagittarius A* , 2005, astro-ph/0507221.

[40]  R. Hulse,et al.  Discovery of a pulsar in a binary system , 1975 .

[41]  J. Hills,et al.  Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole , 1988, Nature.

[42]  P. Amaro-Seoane,et al.  ON STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE: IMPLICATIONS FOR LOWER-FREQUENCY GRAVITATIONAL-WAVE ASTROPHYSICS , 2009, 0910.3206.

[43]  P. Hut.  Binary-single star scattering. II: Analytic approximations for high velocity , 1983 .

[44]  D. Merritt.  THE DISTRIBUTION OF STARS AND STELLAR REMNANTS AT THE GALACTIC CENTER , 2009, 0909.1318.

[45]  C. Hopman,et al.  BINARY DYNAMICS NEAR A MASSIVE BLACK HOLE , 2009, 0906.0374.

[46]  P. Amaro-Seoane,et al.  The impact of realistic models of mass segregation on the event rate of extreme-mass ratio inspirals and cusp re-growth , 2010, 1010.5781.

[47]  MIT,et al.  An Overabundance of Transient X-Ray Binaries within 1 Parsec of the Galactic Center , 2004, astro-ph/0412492.

[48]  Mark R. Morris,et al.  Massive star formation near the Galactic center and the fate of the stellar remnants , 1993 .

[49]  Finding Radio Pulsars in and beyond the Galactic Center , 1996, astro-ph/9608028.

[50]  A. Loeb,et al.  Frequency-dependent Shift in the Image Centroid of the Black Hole at the Galactic Center as a Test of General Relativity , 2005, astro-ph/0508386.

[51]  Using LISA extreme-mass-ratio inspiral sources to test off-Kerr deviations in the geometry of massive black holes , 2006, gr-qc/0612029.

[52]  T. Alexander,et al.  STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE , 2008, 0808.3150.

[53]  P. J. E. Peebles,et al.  Star Distribution Near a Collapsed Object , 1972 .

[54]  E. S. Phinney,et al.  BINARIES IN GLOBULAR CLUSTERS , 1992, astro-ph/9710262.

[55]  A. Loeb,et al.  Production of hypervelocity stars through encounters with stellar‐mass black holes in the Galactic Centre , 2006, astro-ph/0609046.

[56]  I. Stairs,et al.  The double pulsar. , 2008 .

[57]  R. N. Manchester,et al.  Tests of General Relativity from Timing the Double Pulsar , 2006, Science.

[58]  K. Abazajian.  The Consistency of Fermi-LAT Observations of the Galactic Center with a Millisecond Pulsar Population in the Central Stellar Cluster , 2010, 1011.4275.

[59]  D. Thompson,et al.  A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope , 2009, Science.

[60]  L. Ho,et al.  An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations , 2005, astro-ph/0508251.

[61]  Bence Kocsis,et al.  Gravitational waves from scattering of stellar-mass black holes in galactic nuclei , 2008, 0807.2638.

[62]  R. Narayan,et al.  THE BLACK HOLE MASS DISTRIBUTION IN THE GALAXY , 2010, 1006.2834.

[63]  Joseph H. Taylor,et al.  High-precision timing of millisecond pulsars. I - Astrometry and masses of the PSR 1855 + 09 system , 1991 .

[64]  W. N. Brandt,et al.  A Remarkable Low-Mass X-Ray Binary within 0.1 Parsecs of the Galactic Center , 2005, astro-ph/0503572.

[65]  J. Grindlay,et al.  Hubble Space Telescope/NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core , 2002, astro-ph/0202059.

[66]  M. Davies,et al.  Red giant stellar collisions in the Galactic Centre , 2008, 0811.3111.

[67]  Pau Amaro-Seoane,et al.  Stellar Remnants in Galactic Nuclei: Mass Segregation , 2006 .

[68]  John N. Bahcall,et al.  Binary-single star scattering. I: Numerical experiments for equal masses , 1983 .

[69]  Stephen L. W. McMillan,et al.  Binary--Single-Star Scattering. VII. Hard Binary Exchange Cross Sections for Arbitrary Mass Ratios: Numerical Results and Semianalytic FITS , 1996 .

[70]  Mario Livio,et al.  Orbital Capture of Stars by a Massive Black Hole via Exchanges with Compact Remnants , 2004, astro-ph/0403425.

[71]  Steinn Sigurdsson,et al.  Binary-single star interactions in globular clusters , 1993 .

[72]  James Binney,et al.  Galactic Dynamics: Second Edition , 2008 .

[73]  R. Genzel,et al.  MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER , 2008, 0810.4674.

[74]  V. M. Kaspi,et al.  Dynamical Formation of Close Binary Systems in Globular Clusters , 2003 .

[75]  Jessica R. Lu,et al.  Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits , 2008, 0808.2870.

[76]  D. Heggie,et al.  Binary-single-star scattering. IV - Analytic approximations and fitting formulae for cross sections and reaction rates , 1993 .

[77]  Martin J. Rees,et al.  Effects of Massive Central Black Holes on Dense Stellar Systems , 1976 .

[78]  Tomasz Bulik,et al.  A Comprehensive Study of Binary Compact Objects as Gravitational Wave Sources: Evolutionary Channels, Rates, and Physical Properties , 2001, astro-ph/0111452.

[79]  Cnrs,et al.  THE ASTROPHYSICAL JOURNAL, SUBMITTED Preprint typeset using LATEX style emulateapj v. 10/09/06 THE VARIABLE RADIO–TO–X-RAY SPECTRUM OF THE MAGNETAR XTE J1810–197 , 2022 .

[80]  Joseph H. Taylor,et al.  Improved parameters for four binary pulsars , 1988 .

[81]  P. Hut,et al.  SUBMITTED TO APJL Preprint typeset using LATEX style emulateapj v. 6/22/04 DYNAMICAL FORMATION OF CLOSE BINARIES IN GLOBULAR CLUSTERS II: CATACLYSMIC VARIABLES , 2006 .

[82]  I. Stairs.  Testing General Relativity with Pulsar Timing , 2003, Living reviews in relativity.

[83]  M. Kramer.  Fundamental Physics with the SKA: Strong-Field Tests of Gravity Using Pulsars and Black Holes , 2004, astro-ph/0409020.

[84]  RELATIVISTIC BINARY PULSARS WITH BLACK HOLE COMPANIONS , 2005, astro-ph/0502122.

[85]  The Effect of Encounters on the Eccentricity of Binaries in Clusters , 1995, astro-ph/9506082.

[86]  Discovery of two pulsars towards the Galactic Centre , 2006, astro-ph/0606465.

[87]  T. Alexander,et al.  ANALYTIC STUDY OF MASS SEGREGATION AROUND A MASSIVE BLACK HOLE , 2009, 0901.4343.

[88]  S. Ransom,et al.  A 1.4 GHz Arecibo Survey for Pulsars in Globular Clusters , 2007, 0707.1602.

[89]  Pasadena,et al.  HIGH ANGULAR RESOLUTION INTEGRAL-FIELD SPECTROSCOPY OF THE GALAXY'S NUCLEAR CLUSTER: A MISSING STELLAR CUSP? , 2009, 0908.0311.

[90]  C. Cesarsky,et al.  Exploring the Cosmic Frontier , 2007 .

[91]  Richard A. Wolf,et al.  Star distribution around a massive black hole in a globular cluster , 1976 .

[92]  P. Hut.  Binaries as a heat source in stellar dynamics: release of binding energy , 1983 .

[93]  E. Phinney.  The Rate of Neutron Star Binary Mergers in the Universe: Minimal Predictions for Gravity Wave Detectors , 1991 .

[94]  India,et al.  A HIGH-FREQUENCY SEARCH FOR PULSARS WITHIN THE CENTRAL PARSEC OF Sgr A* , 2010, 1004.1643.

[95]  G. Drukier.  RETENTION FRACTIONS FOR GLOBULAR CLUSTER NEUTRON STARS , 1995, astro-ph/9512163.

[96]  M. Kramer,et al.  Observations of Pulsars at 7 Millimeters , 1997 .

[97]  Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center , 1998, astro-ph/9804157.

[98]  Emil Khalisi,et al.  A comprehensive nbody study of mass segregation in star clusters: energy equipartition and escape , 2006, astro-ph/0602570.

[99]  C. Kim,et al.  An increased estimate of the merger rate of double neutron stars from observations of a highly relativistic system , 2003, Nature.

[100]  M. Miller,et al.  MERGERS OF STELLAR-MASS BLACK HOLES IN NUCLEAR STAR CLUSTERS , 2008, 0804.2783.

[101]  A. Loeb,et al.  The pulsar contribution to the gamma-ray background , 2009, 0904.3102.

[102]  P. C. Peters.  Gravitational Radiation and the Motion of Two Point Masses , 1964 .

[103]  T. Alexander,et al.  Enhanced Microlensing by Stars around the Black Hole in the Galactic Center , 2000, astro-ph/0009404.

[104]  A. Gould,et al.  Microlensing by Stellar Black Holes around Sagittarius A* , 2001, astro-ph/0102481.