# Coupling of radial and axial nonradial oscillations of compact stars: Gravitational waves from first-order differential rotation

## Abstract

We investigate the nonlinear coupling between radial and nonradial oscillations of static spherically-symmetric neutron stars as a possible mechanism for the generation of gravitational waves that may lead to observable signatures. In this paper we concentrate on the axial sector of the nonradial perturbations. By using a multiparameter perturbative framework we introduce a complete description of the nonlinear coupling between radial and axial nonradial oscillations; we study the gauge-invariant character of the associated perturbative variables and develop a computational scheme to evolve the nonlinear coupling perturbations in the time domain. We present results of simulations corresponding to different physical situations and discuss the dynamical behavior of this nonlinear coupling. Of particular interest is the occurrence of signal amplifications in the form of resonance phenomena when a frequency associated with the radial pulsations is close to a frequency associated with one of the axial w-modes of the star. Finally, we mention possible extensions of this work and improvements towards more astrophysically motivated scenarios.

- Authors:

- Institute of Cosmology and Gravitation, University of Portsmouth, Mercantile House, Portsmouth PO1 2EG (United Kingdom)
- (Greece)
- (Italy)
- Centro Studi e Ricerche E. Fermi, Compendio Viminale, 00184 Rome (Italy) and Dipartimento di Fisica 'G. Marconi', Universita di Roma 'La Sapienza'/Sezione INFN ROMA 1, P.le Aldo Moro 2, I-00185 Rome (Italy)
- Dipartimento di Fisica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin (Italy) and INFN sez. di Torino, Via P. Giuria 1, Turin (Italy)
- Institute for Gravitational Physics and Geometry, Center for Gravitational Wave Physics, and Department of Astronomy and Astrophysics, Penn State University, University Park, Pennsylvania 16802 (United States)

- Publication Date:

- OSTI Identifier:
- 20782909

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 8; Other Information: DOI: 10.1103/PhysRevD.73.084010; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; AMPLIFICATION; COSMOLOGY; COUPLING; DISTURBANCES; GAUGE INVARIANCE; GRAVITATIONAL WAVES; NEUTRON STARS; NONLINEAR PROBLEMS; OSCILLATIONS; PERTURBATION THEORY; PULSATIONS; RESONANCE; ROTATION; SIMULATION

### Citation Formats

```
Passamonti, Andrea, Department of Physics, Aristotle University of Thessaloniki 54124, Bruni, Marco, Dipartimento di Fisica, Universita degli Studi di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Rome, Gualtieri, Leonardo, Nagar, Alessandro, and Sopuerta, Carlos F.
```*Coupling of radial and axial nonradial oscillations of compact stars: Gravitational waves from first-order differential rotation*. United States: N. p., 2006.
Web. doi:10.1103/PHYSREVD.73.084010.

```
Passamonti, Andrea, Department of Physics, Aristotle University of Thessaloniki 54124, Bruni, Marco, Dipartimento di Fisica, Universita degli Studi di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Rome, Gualtieri, Leonardo, Nagar, Alessandro, & Sopuerta, Carlos F.
```*Coupling of radial and axial nonradial oscillations of compact stars: Gravitational waves from first-order differential rotation*. United States. doi:10.1103/PHYSREVD.73.084010.

```
Passamonti, Andrea, Department of Physics, Aristotle University of Thessaloniki 54124, Bruni, Marco, Dipartimento di Fisica, Universita degli Studi di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Rome, Gualtieri, Leonardo, Nagar, Alessandro, and Sopuerta, Carlos F. Sat .
"Coupling of radial and axial nonradial oscillations of compact stars: Gravitational waves from first-order differential rotation". United States.
doi:10.1103/PHYSREVD.73.084010.
```

```
@article{osti_20782909,
```

title = {Coupling of radial and axial nonradial oscillations of compact stars: Gravitational waves from first-order differential rotation},

author = {Passamonti, Andrea and Department of Physics, Aristotle University of Thessaloniki 54124 and Bruni, Marco and Dipartimento di Fisica, Universita degli Studi di Roma 'Tor Vergata', via della Ricerca Scientifica 1, 00133 Rome and Gualtieri, Leonardo and Nagar, Alessandro and Sopuerta, Carlos F.},

abstractNote = {We investigate the nonlinear coupling between radial and nonradial oscillations of static spherically-symmetric neutron stars as a possible mechanism for the generation of gravitational waves that may lead to observable signatures. In this paper we concentrate on the axial sector of the nonradial perturbations. By using a multiparameter perturbative framework we introduce a complete description of the nonlinear coupling between radial and axial nonradial oscillations; we study the gauge-invariant character of the associated perturbative variables and develop a computational scheme to evolve the nonlinear coupling perturbations in the time domain. We present results of simulations corresponding to different physical situations and discuss the dynamical behavior of this nonlinear coupling. Of particular interest is the occurrence of signal amplifications in the form of resonance phenomena when a frequency associated with the radial pulsations is close to a frequency associated with one of the axial w-modes of the star. Finally, we mention possible extensions of this work and improvements towards more astrophysically motivated scenarios.},

doi = {10.1103/PHYSREVD.73.084010},

journal = {Physical Review. D, Particles Fields},

number = 8,

volume = 73,

place = {United States},

year = {Sat Apr 15 00:00:00 EDT 2006},

month = {Sat Apr 15 00:00:00 EDT 2006}

}