C.D.S. - SIMBAD4 rel 1.7 - 2020.01.26CET02:49:56

2018A&A...620A..69H - Astronomy and Astrophysics, volume 620A, 69-69 (2018/12-1)

Fundamental physics and the absence of sub-millisecond pulsars.


Abstract (from CDS):

Context. Rapidly rotating neutron stars are an ideal laboratory to test models of matter at high densities. In particular, the maximum rotation frequency of a neutron star depends on the equation of state and can be used to test models of the interior. However, observations of the spin distribution of rapidly rotating neutron stars show evidence for a lack of stars spinning at frequencies higher than f~=700Hz, well below the predictions of theoretical equations of state. This has generally been taken as evidence of an additional spin-down torque operating in these systems, and it has been suggested that gravitational wave torques may be operating and be linked to a potentially observable signal.
Aims. We aim to determine whether additional spin-down torques (possibly due to gravitational wave emission) are necessary, or if the observed limit of f~=700Hz could correspond to the Keplerian (mass-shedding) break-up frequency for the observed systems, and is simply a consequence of the currently unknown state of matter at high densities.
Methods. Given our ignorance with regard to the true equation of state of matter above nuclear saturation densities, we make a minimal physical assumption and only demand causality, that is, that the speed of sound in the interior of the neutron star should be lower than or equal to the speed of light c. We then connected our causally limited equation of state to a realistic microphysical crustal equation of state for densities below nuclear saturation density. This produced a limiting model that gave the lowest possible maximum frequency, which we compared to observational constraints on neutron star masses and frequencies. We also compared our findings with the constraints on the tidal deformability obtained in the observations of the GW170817 event.
Results. We rule out centrifugal breakup as the mechanism preventing pulsars from spinning faster than f~=700Hz, as the lowest breakup frequency allowed by our causal equation of state is f~=1200Hz. A low-frequency cutoff, around f~=800Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M~=2M. This would have to be due either to selection effects, or possibly to a phase transition in the interior of the neutron star that leads to softening at high densities and a collapse to either a black hole or a hybrid star above M~=2M. Such a scenario would, however, require a somewhat unrealistically stiff equation of state for hadronic matter, in tension with recent constraints obtained from gravitational wave observations of a neutron star merger.

Abstract Copyright: © ESO 2018

Journal keyword(s): dense matter - stars: neutron - X-rays: binaries

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
1 PSR J0337+1715 Psr 03 37 43.82589 +17 15 14.8280           ~ 63 0
2 PSR J0348+0432 Psr 03 48 43.6365407296 +04 32 11.460202882           ~ 132 1
3 PSR J1023+0038 LXB 10 23 47.6840307966 +00 38 41.006983532     17.31     GV 293 0
4 GrW 170817 GWE 13 09 48.0850 -23 22 53.343           ~ 620 0
5 PSR J1311-3430 Psr 13 11 50 -34 30.1           ~ 105 1
6 PSR J1614-2230 Psr 16 14 36.5070 -22 30 31.207           ~ 259 1
7 PSR J1748-2446ad Psr 17 48 04.9 -24 46 04           ~ 78 1
8 PSR J1903+0327 Psr 19 03 05.7937 +03 27 19.222           ~ 120 1
9 PSR J1959+2048 Psr 19 59 36.7480 +20 48 14.599   20.4       ~ 685 2
10 PSR J2043+1711 Psr 20 43 20.8828 +17 11 28.941           ~ 68 1
11 PSR J2215+51 Psr 22 15 32.6864199137 +51 35 36.406276103           ~ 80 0

    Equat.    Gal    SGal    Ecl

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