Gravitational Waves from Neutron Star and Black Hole Mergers

• Applicant: Professor Dr. Bernd Brügmann
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 360292238

• Final Report Year: 2023

Final Report Abstract

The first direct detection of gravitational waves in 2015 was a historic breakthrough in gravitational physics, leading to a Nobel Prize in 2017. The first signals were identified as merger events of two black holes, followed also by observations of neutron star mergers, which demonstrated that mergers of compact binaries are indeed primary candidates for gravitational wave sources. The focus of the project was on compact binaries involving neutron stars, either in a neutron star binary or a binary formed by a neutron star and a black hole, which are described by general relativity coupled to general relativistic hydrodynamics. The data analysis and parameter estimation for merger events rely on numerical simulations that solve the two-body problem of Einstein’s general theory of relativity in the highly-dynamic strong-field regime. The goal in general is to provide theoretical models for the relativistic dynamics, the merger process with ejecta and torus formation, and the generation of gravitational waves. The system that had been predominantly studied in numerical relativity was non-spinning neutron stars of equal or comparable mass on quasi-circular orbits. The project succeeded in several regards to overcome theoretical and technical limitations to go significantly beyond the first proof-of-principle calculations, in particular by including spin. By varying the spins, masses and eccentricity of the binary, the long-term goal is to thereby complete the gravitational parameter space accessible to numerical relativity and to prepare for the corresponding gravitational wave observations that are expected in the future. Among key results of the project is work on the effect of spin and eccentricity on gravitational waves and mass ejecta from binary neutron star mergers. Tidal deformations can become relevant, for which semi-analytical and analytical models are developed. An important aspect of numerical evolutions is the construction of physically appropriate initial data, which was considered by various methods for high spins, high compactness, and high mass ratios of the neutron stars. The work includes concrete applications to current observations. The numerical data has contributed to one of the largest public data bases for neutron star mergers.

Publications

• Gravitational waves and mass ejecta from binary neutron star mergers: Effect of large eccentricities. Physical Review D, 98(10).
  Chaurasia, Swami Vivekanandji; Dietrich, Tim; Johnson-McDaniel, Nathan K.; Ujevic, Maximiliano; Tichy, Wolfgang & Brügmann, Bernd
  
• Relevance of tidal effects and post-merger dynamics for binary neutron star parameter estimation. Physical Review D, 98(8).
  Dudi, Reetika; Pannarale, Francesco; Dietrich, Tim; Hannam, Mark; Bernuzzi, Sebastiano; Ohme, Frank & Brügmann, Bernd
  
• Constructing binary neutron star initial data with high spins, high compactnesses, and high mass ratios. Physical Review D, 100(12).
  Tichy, Wolfgang; Rashti, Alireza; Dietrich, Tim; Dudi, Reetika & Brügmann, Bernd
  
• Improving the NRTidal model for binary neutron star systems. Physical Review D, 100(4).
  Dietrich, Tim; Samajdar, Anuradha; Khan, Sebastian; Johnson-McDaniel, Nathan K.; Dudi, Reetika & Tichy, Wolfgang
  
• Quasi-5.5PN TaylorF2 approximant for compact binaries: Point-mass phasing and impact on the tidal polarizability inference. Physical Review D, 99(12).
  Messina, Francesco; Dudi, Reetika; Nagar, Alessandro & Bernuzzi, Sebastiano
  
• Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the spin orientation. Physical Review D, 102(2).
  Chaurasia, Swami Vivekanandji; Dietrich, Tim; Ujevic, Maximiliano; Hendriks, Kai; Dudi, Reetika; Fabbri, Francesco Maria; Tichy, Wolfgang & Brügmann, Bernd
  
• Gravitational waves from binary neutron stars systems. Ph.D. thesis, Friedrich Schiller University, Jena, Germany (2020)
  R. Dudi
  
• Increasing the accuracy of binary neutron star simulations with an improved vacuum treatment. Physical Review D, 102(10).
  Poudel, Amit; Tichy, Wolfgang; Brügmann, Bernd & Dietrich, Tim
  
• Thermodynamics conditions of matter in the neutrino decoupling region during neutron star mergers. The European Physical Journal A, 56(1).
  Endrizzi, Andrea; Perego, Albino; Fabbri, Francesco M.; Branca, Lorenzo; Radice, David; Bernuzzi, Sebastiano; Giacomazzo, Bruno; Pederiva, Francesco & Lovato, Alessandro
  
• Compact binary merger simulations in numerical relativity. Ph.D. thesis, Friedrich Schiller University, Jena, Germany (2022)
  F. Fabbri
  
• High-accuracy simulations of highly spinning binary neutron star systems. Physical Review D, 105(6).
  Dudi, Reetika; Dietrich, Tim; Rashti, Alireza; Brügmann, Bernd; Steinhoff, Jan & Tichy, Wolfgang
  
• Investigating GW190425 with numerical-relativity simulations. Physical Review D, 106(8).
  Dudi, Reetika; Adhikari, Ananya; Brügmann, Bernd; Dietrich, Tim; Hayashi, Kota; Kawaguchi, Kyohei; Kiuchi, Kenta; Kyutoku, Koutarou; Shibata, Masaru & Tichy, Wolfgang
  
• New pseudospectral code for the construction of initial data. Physical Review D, 105(10).
  Rashti, Alireza; Fabbri, Francesco Maria; Brügmann, Bernd; Chaurasia, Swami Vivekanandji; Dietrich, Tim; Ujevic, Maximiliano & Tichy, Wolfgang