Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes

Abstract

Can one distinguish a binary black hole undergoing a merger from a binary neutron star if the individual compact companions have masses that fall inside the so-called mass gap of $3-5M_{\odot }$? For neutron stars, achieving such masses typically requires extreme compactness and in this work we present initial data and evolutions of binary neutron stars initially in quasiequilibrium circular orbits having a compactness $C=0.336$. These are the most compact, nonvacuum, quasiequilibrium binary objects that have been constructed and evolved to date, including boson stars. The compactness achieved is only slightly smaller than the maximum possible imposed by causality, $C_{\max }=0.355$, which requires the sound speed to be less than the speed of light. By comparing the emitted gravitational waveforms from the late inspiral to merger and postmerger phases between such a binary neutron star vs a binary black hole of the same total mass we identify concrete measurements that serve to distinguish them. With that level of compactness, the binary neutron stars exhibit no tidal disruption up until merger, whereupon a prompt collapse is initiated even before a common core forms. Within the accuracy of our simulations the black hole remnants from both binaries exhibit ringdown radiation that is not distinguishable from a perturbed Kerr spacetime. However, their inspiral leads to phase differences of the order of $\sim 5$ rad over an $\sim 81$ km separation (1.7 orbits) while typical neutron stars exhibit phase differences of $\ge 20$ rad. Although a difference of $\sim 5$ rad can be measured by current gravitational wave laser interferometers (e.g., aLIGO/Virgo), uncertainties in the individual masses and spins will likely prevent distinguishing such compact, massive neutron stars from black holes.

arXiv comment8 pages, 9 figures. Matches published version

References in corpus (49)

• Observation of Gravitational Waves from a Binary Black Hole Merger
• Quasi-Normal Modes of Stars and Black Holes
• Gravitational Waves from Mergin Compact Binaries: How Accurately Can One Extract the Binary's Parameters from the Inspiral Waveform?
• Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar
• On the Numerical Integration of Einstein's Field Equations
• The Nuclear Equation of State and Neutron Star Masses
• On gravitational-wave spectroscopy of massive black holes with the space interferometer LISA
• Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817
• Using gravitational-wave observations and quasi-universal relations to constrain the maximum mass of neutron stars
• Hybrid stars that masquerade as neutron stars
• FINDCHIRP: an algorithm for detection of gravitational waves from inspiraling compact binaries
• The Equation of State of Hot, Dense Matter and Neutron Stars
• GW170817, General Relativistic Magnetohydrodynamic Simulations, and the Neutron Star Maximum Mass
• A single-domain spectral method for black hole puncture data
• Accurate evolutions of inspiralling neutron-star binaries: prompt and delayed collapse to black hole
• Introduction to Isolated Horizons in Numerical Relativity
• Constraint on the maximum mass of neutron stars using GW170817 event
• Quasiequilibrium sequences of synchronized and irrotational binary neutron stars in general relativity. I. Method and tests
• Improving the NRTidal model for binary neutron star systems
• A multidomain spectral method for solving elliptic equations
• Fully General Relativistic Simulations of Black Hole-Neutron Star Mergers
• Constructing Gravitational Waves from Generic Spin-Precessing Compact Binary Inspirals
• Relativistic simulations of black hole-neutron star coalescence: the jet emerges
• Gravitational Wave Signatures of Highly Compact Boson Star Binaries
• Upper Limit Set by Causality on the Rotation and Mass of Uniformly Rotating Relativistic Stars
• When can gravitational-wave observations distinguish between black holes and neutron stars?
• Relativistic magnetohydrodynamics in dynamical spacetimes: A new AMR implementation
• Observing and measuring the neutron-star equation-of-state in spinning binary neutron star systems
• General relativistic simulations of black hole-neutron star mergers: Effects of magnetic fields
• Sub-radian-accuracy gravitational waveforms of coalescing binary neutron stars in numerical relativity
• Initial data for black hole-neutron star binaries: a flexible, high-accuracy spectral method
• Quasiequilibrium sequences of synchronized and irrotational binary neutron stars in general relativity. III. Identical and different mass stars with gamma=2
• Lennard-Jones quark matter and massive quark stars
• General relativistic simulations of black hole-neutron star mergers: Effects of tilted magnetic fields
• The Evolution of Distorted Rotating Black Holes II: Dynamics and Analysis
• A new numerical method to construct binary neutron star initial data
• Neutron stars versus black holes: probing the mass gap with LIGO/Virgo
• Can we distinguish low mass black holes in neutron star binaries?
• Initial data for binary neutron stars with arbitrary spins
• Distinguishing types of compact-object binaries using the gravitational-wave signatures of their mergers
• A new code for equilibriums and quasiequilibrium initial data of compact objects
• Effect of spin on the inspiral of binary neutron stars
• Binary Neutron Stars in Quasi-equilibrium
• On the dynamical stability of quasi-toroidal differentially rotating neutron stars
• Initial-data contribution to the error budget of gravitational waves from neutron-star binaries
• Uniformly rotating, axisymmetric and triaxial quark stars in general relativity
• Constant circulation sequences of binary neutron stars and their spin characterization
• Dynamically stable ergostars exist: General relativistic models and simulations
• Initial data for high-compactness black hole-neutron star binaries

Cited by in corpus (16)

• Discriminating between Neutron Stars and Black Holes with Imperfect Knowledge of the Maximum Neutron Star Mass
• Constraints on the maximum mass of neutron stars with a quark core from GW170817 and NICER PSR J0030+0451 data
• Constraining hadron-quark phase transition parameters within the quark-mean-field model using multimessenger observations of neutron stars
• Jet Launching from Binary Neutron Star Mergers: Incorporating Neutrino Transport and Magnetic Fields
• Distinguishing high-mass binary neutron stars from binary black holes with second- and third-generation gravitational wave observatories
• Thermodynamical Description of Hot, Rapidly Rotating Neutron Stars, Protoneutron Stars, and Neutron Star Merger Remnants
• Multimessenger Binary Mergers Containing Neutron Stars: Gravitational Waves, Jets, and $\mathbf{\gamma }$-Ray Bursts
• Jet Launching from Merging Magnetized Binary Neutron Stars with Realistic Equations of State
• Distinguishing double neutron star from neutron star-black hole binary populations with gravitational wave observations
• Distinguishing the nature of ''ambiguous'' merging systems hosting a neutron star: GW190425 in low-latency
• Black hole-neutron star coalescence: effects of the neutron star spin on jet launching and dynamical ejecta mass
• Locating ergostar models in parameter space
• Neutron Stars and Gravitational Waves: the Key Role of Nuclear Equation of State
• Methods for relativistic self-gravitating fluids: From binary neutron stars to black hole-disks and magnetized rotating neutron stars
• Fully general-relativistic simulations of isolated and binary strange quark stars
• Characterizing Compact-object Binaries in the Lower Mass Gap with Gravitational Waves