Monopolar and quadrupolar gravitational radiation from magnetically deformed neutron stars in modified gravity

Abstract

Some modified theories of gravity are known to predict monopolar, in addition to the usual quadrupolar and beyond, gravitational radiation in the form of `breathing' modes. For the same reason that octupole and higher-multipole terms often contribute negligibly to the overall wave strain, monopole terms tend to dominate. We investigate both monopolar and quadrupolar continuous gravitational radiation from neutron stars deformed through internal magnetic stresses. We adopt the Parameterised-Post-Newtonian formalism to write down equations describing the leading-order stellar properties in a theory-independent way, and derive some exact solutions for stars with mixed poloidal-toroidal magnetic fields. We then turn to the specific case of scalar-tensor theories to demonstrate how observational upper limits on the gravitational-wave luminosity of certain neutron stars may be used to place constraints on modified gravity parameters, most notably the Eddington parameter $\gamma$. For conservative, purely poloidal models with characteristic field strength given by the spindown minimum, upper limits for the Vela pulsar yield $1-\gamma \lesssim 4.2\times 10^{-3}$. For models containing a strong toroidal field housing $\sim 99\%$ of the internal magnetic energy, we obtain the bound $1-\gamma \lesssim 8.0\times 10^{-7}$. This latter bound is an order of magnitude tighter than those obtained from current Solar system experiments, though applies to the strong-field regime.

13 pages, 6 figures, 1 table. Accepted for publication in Phys. Rev. D

References in corpus (16)

• The Confrontation between General Relativity and Experiment
• A Massive Pulsar in a Compact Relativistic Binary
• LIGO: The Laser Interferometer Gravitational-Wave Observatory
• Extreme neutron stars from Extended Theories of Gravity
• Modelling magnetically deformed neutron stars
• Probing non-tensorial polarizations of stochastic gravitational-wave backgrounds with ground-based laser interferometers
• Energy-momentum complexes in f(R) theories of gravity
• Creation of magnetic spots at the neutron star surface
• Neutron star deformation due to poloidal-toroidal magnetic fields of arbitrary multipole order: a new analytic approach
• Multipole moments in scalar-tensor theory of gravity
• Gravitational Wave Memory: A New Approach to Study Modified Gravity
• Testing scalar-tensor theories and PPN parameters in Earth orbit
• Cooling of Neutron Stars with Strong Toroidal Magnetic Fields
• Impact of the equation-of-state -- gravity degeneracy on constraining the nuclear symmetry energy from astrophysical observables
• On Gravitational Radiation in Quadratic $f(R)$ Gravity
• Astroseismology of neutron stars from gravitational waves in the limit of perfect measurement

Cited by in corpus (7)

• Stellar structure models in modified theories of gravity: lessons and challenges
• Young magnetars with fracturing crusts as fast radio burst repeaters
• Gravitational perturbations of a Kerr black hole in $f(R)$ gravity
• Axisymmetric equilibrium models for magnetised neutron stars in Scalar-Tensor Theories
• Relaxation by thermal conduction of a magnetically confined mountain on an accreting neutron star
• Premerger phenomena in neutron-star binary coalescences
• Lensing by black holes within astrophysical environments