Gravitational waves from deformed neutron stars: mountains and tides. (arXiv:2109.07858v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gittins_F/0/1/0/all/0/1">Fabian Gittins</a>
With the remarkable advent of gravitational-wave astronomy, we have shed
light on previously shrouded events: compact binary coalescences. Neutron stars
are promising (and confirmed) sources of gravitational radiation and it proves
timely to consider the ways in which these stars can be deformed. Gravitational
waves provide a unique window through which to examine neutron-star interiors
and learn more about the equation of state of ultra-dense nuclear matter. In
this work, we study two relevant scenarios for gravitational-wave emission:
neutron stars that host (non-axially symmetric) mountains and neutron stars
deformed by the tidal field of a binary partner. Although they have yet to be
seen with gravitational waves, rotating neutron stars have long been considered
potential sources. By considering the observed spin distribution of accreting
neutron stars with a phenomenological model for the spin evolution, we find
evidence for gravitational radiation in these systems. We study how mountains
are modelled in both Newtonian and relativistic gravity and introduce a new
scheme to resolve issues with previous approaches to this problem. The crucial
component of this scheme is the deforming force that gives the star its
non-spherical shape. We find that the force (which is a proxy for the star’s
formation history), as well as the equation of state, plays a pivotal role in
supporting the mountains. Considering a scenario that has been observed with
gravitational waves, we calculate the structure of tidally deformed neutron
stars, focusing on the impact of the crust. We find that the effect on the
tidal deformability is negligible, but the crust will remain largely intact up
until merger.
With the remarkable advent of gravitational-wave astronomy, we have shed
light on previously shrouded events: compact binary coalescences. Neutron stars
are promising (and confirmed) sources of gravitational radiation and it proves
timely to consider the ways in which these stars can be deformed. Gravitational
waves provide a unique window through which to examine neutron-star interiors
and learn more about the equation of state of ultra-dense nuclear matter. In
this work, we study two relevant scenarios for gravitational-wave emission:
neutron stars that host (non-axially symmetric) mountains and neutron stars
deformed by the tidal field of a binary partner. Although they have yet to be
seen with gravitational waves, rotating neutron stars have long been considered
potential sources. By considering the observed spin distribution of accreting
neutron stars with a phenomenological model for the spin evolution, we find
evidence for gravitational radiation in these systems. We study how mountains
are modelled in both Newtonian and relativistic gravity and introduce a new
scheme to resolve issues with previous approaches to this problem. The crucial
component of this scheme is the deforming force that gives the star its
non-spherical shape. We find that the force (which is a proxy for the star’s
formation history), as well as the equation of state, plays a pivotal role in
supporting the mountains. Considering a scenario that has been observed with
gravitational waves, we calculate the structure of tidally deformed neutron
stars, focusing on the impact of the crust. We find that the effect on the
tidal deformability is negligible, but the crust will remain largely intact up
until merger.
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