Rotational modes of relativistic stars: Higher order equations

Date

2022-08

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Abstract

The structure and composition of Neutron Stars (NSs) are unknown and the most promising way to understand them is through Gravitational Wave (GW) as- teroseismology, that is the study of the oscillations of the star through GWs. Of all the possible Quasi Normal Modes (QNMs), the r-modes are the most promis- ing source of GWs because they can be unstable at an arbitrary angular velocity, due to the Chandrasekhar-Friedman-Schutz (CFS) instability mechanism. Other QNMs either are stable, which means that their amplitude are damped, or their instability turns on at very high angular velocities. This means that these other modes would be hardly detectable. The frequencies of r-mode oscillations of rotating NSs can be useful for guiding and interpreting GW and electromagnetic observations, which makes this study of relevance to both LIGO scientists and astrophysicists. The frequencies of slowly ro- tating, barotropic and non-magnetic Newtonian stars are well known, but subject to various corrections. The most important one is the relativistic correction, and the second most important is the rapid rotation correction. For this reason we decided to study the Lockitch-Andersson-Friedman (LAF) equations, that describe r-mode oscillations of stars in General Relativity (GR), and we extended these equations to higher order in the rotation rate expansion. In this work we derived these higher order versions of the LAF equations. Solving these equations would allow us to find a more precise range of frequencies than the one found by Idrisy, Owen and Jones [27]. In addition, it will help to better guide scientists in LIGO searches, and in case of detection, to guide astrophysicists in EM searches1. More importantly, a detection, together with a numerical calcula- tion of our equations, would allow us to put more constraints on the Equation Of State (EOS) and therefore to better understand the physics of NS cores.


Embargo status: Restricted until 09/2023. To request the author grant access, click on the PDF link to the left.

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Restricted until 09/2023.

Keywords

Neutron Stars, r-modes, Gravitational Waves, Equation of State, Quasi Normal Modes

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