Oscillation modes of rapidly rotating neutron stars in scalar-tensor theories of gravity

Stoytcho S. Yazadjiev, Daniela D. Doneva, and Kostas D. Kokkotas
Phys. Rev. D 96, 064002 – Published 5 September 2017

Abstract

We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental f modes. We concentrated on a particular class of alternative theories—the (massive) scalar-tensor theories. The generalization to rapid rotation is important because on one hand the rapid rotation can magnify the deviations from general relativity compared to the static case and on the other hand some of the most efficient emitters of gravitational radiation, such as the binary neutron star merger remnants, are supposed to be rotating close to their Kepler (mass-shedding) limits shortly after their formation. We have constructed several sequences of models starting from the nonrotating case and reaching up to the Kepler limit, with different values of the scalar-tensor theory coupling constant and the scalar field mass. The results show that the deviations from pure Einstein’s theory can be significant, especially in the case of nonzero scalar field mass. An important property of the oscillation modes of rapidly rotating stars is that they can become secularly unstable due to the emission of gravitational radiation, the so-called Chandrasekhar-Friedman-Schutz instability. Such unstable modes are efficient emitters of gravitational radiation. Our studies show that the inclusion of a nonzero scalar field would decrease the threshold value of the normalized angular momentum where this instability starts to operate, but the growth time of the instability seems to be increased compared to pure general relativity.

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  • Received 14 June 2017

DOI:https://doi.org/10.1103/PhysRevD.96.064002

© 2017 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Stoytcho S. Yazadjiev1,2,*, Daniela D. Doneva2,3,†, and Kostas D. Kokkotas2,‡

  • 1Department of Theoretical Physics, Faculty of Physics, Sofia University, Sofia 1164, Bulgaria
  • 2Theoretical Astrophysics, Eberhard-Karls University of Tübingen, Tübingen 72076, Germany
  • 3INRNE—Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria

  • *yazad@phys.uni-sofia.bg
  • daniela.doneva@uni-tuebingen.de
  • kostas.kokkotas@uni-tuebingen.de

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Issue

Vol. 96, Iss. 6 — 15 September 2017

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