Rotational Mass of Anisotropic Neutron Stars in Rastall Gravity

核心概念

The rotational mass of anisotropic neutron stars is significantly impacted by the Rastall gravity parameter and the anisotropic strength, with the anisotropic strength being the dominant factor. The mass constraints of observed neutron stars, including the heaviest known, can be satisfied by the model with strong anisotropic strength.

摘要

The authors extend the formulation of the rotational mass of anisotropic neutron stars (NSs) within the Hartle-Thorne-Rastall (HTR) framework. They use the anisotropic pressure model proposed by Horvat et al. and the equation of state with nuclei in the crust and hyperons in the core, proposed by Miyatsu et al.
The key findings are:

Both the Rastall gravity parameter (λ) and the anisotropic strength (ζ) impact the increment of the NS's rotational mass within the compact regimes, and the decrease within the loose regimes. The anisotropic strength is the dominant factor in increasing the rotational mass.

All mass constraints, including the heaviest known NS (GW190814), can be satisfied by the model with ζ = -2.00. This is an improvement over previous works that could not reach the mass range of GW190814.

The Rastall parameter reduces the radius of NSs, while the anisotropic strength also slightly decreases the radius. However, neither λ nor ζ have a significant impact on the relation between central pressure and radius.

The anisotropic strength magnifies the moment of inertia of NSs, while the Rastall parameter decreases it before the peak and increases it after the peak. All results match the constraint range based on radio observations of heavy pulsars.

The mass correction due to rotation significantly increases as the angular velocity relative to distant observers increases, and this increment is not linear.

統計資料

The mass constraints used in this study are:

J0740+6620 with mass of 2.08+0.07-0.07 M⊙
GW170817 with heaviest object mass in the range of 1.36-2.26 M⊙
GW190814 with secondary object mass in the range of 2.50-2.67 M⊙

引述

"All mass constraints are satisfied by the NS with ζ = −2.00."
"The anisotropic strength magnifies the value of I; while Rastall's parameter decreases the moment of inertia in the regime before the peak, and increases the moment of inertia in the regime after the peak."
"In term of the angular velocity of the stars relative to the distant observers Ω, the mass correction δM significantly increases when Ωincreases, and the increment of the δM is not linear to the increment of Ω."

從以下內容提煉的關鍵洞見

Rotational mass of anisotropic neutron stars within Rastall gravity

by M. Lawrence ... 於 arxiv.org 10-03-2024

https://arxiv.org/pdf/2404.01837.pdf

深入探究

How would the results change if a different anisotropic pressure model or equation of state were used?

The results of the study on the rotational mass of anisotropic neutron stars (NSs) within Rastall gravity would likely vary significantly if a different anisotropic pressure model or equation of state (EOS) were employed. The anisotropic pressure model used in this study, proposed by Horvat et al., establishes a specific relationship between radial and tangential pressures, which directly influences the stability and structure of the NS. If an alternative model were applied, such as the Bowers-Liang model, which has different assumptions about pressure anisotropy, the resulting mass-radius relations and rotational mass calculations could yield different outcomes.
Moreover, the choice of EOS is crucial as it dictates the relationship between pressure, density, and temperature within the NS. The EOS used in this study incorporates hyperons in the core and nuclei in the crust, which is more realistic for describing the dense matter in NSs. If a simpler or different EOS were utilized, such as a polytropic EOS, it might not capture the complex interactions present in the dense matter, leading to an underestimation or overestimation of the maximum mass and radius of the NS. Consequently, the mass constraints derived from observations, such as those from J0740+6620, GW170817, and GW190814, could be affected, potentially failing to satisfy the observational limits if the EOS does not adequately represent the physical conditions within the NS.

What are the potential observational signatures that could distinguish between Rastall gravity and general relativity in the context of neutron stars?

In the context of neutron stars, several potential observational signatures could help distinguish between Rastall gravity and general relativity (GR). One of the most significant differences lies in the mass-radius relationship of NSs. Rastall gravity introduces a parameter (λ) that modifies the equations governing the structure of NSs, potentially leading to different predictions for the maximum mass and radius compared to GR. Observations of pulsar timing and gravitational wave events, such as those from the LIGO/Virgo collaboration, could provide critical data to test these predictions.
Additionally, the moment of inertia (I) of NSs is another observable quantity that could reveal differences between the two theories. The study indicates that Rastall gravity affects the moment of inertia in a way that depends on the anisotropic strength (ζ) and the Rastall parameter (λ). If future observations can measure the moment of inertia of NSs with high precision, discrepancies between the predicted values from Rastall gravity and those from GR could emerge.
Gravitational wave signals from neutron star mergers may also exhibit differences in the waveforms predicted by Rastall gravity compared to GR. The presence of anisotropy and the modified field equations could alter the dynamics of the merger process, leading to unique signatures in the gravitational wave signals that could be detected by observatories.

How might the insights from this study on the impact of anisotropy and Rastall gravity inform our understanding of the internal structure and composition of the most massive neutron stars?

The insights gained from this study on the impact of anisotropy and Rastall gravity significantly enhance our understanding of the internal structure and composition of the most massive neutron stars. The findings suggest that the anisotropic strength (ζ) plays a crucial role in determining the rotational mass and stability of NSs. A stronger anisotropic pressure could allow for the support of more massive NSs against gravitational collapse, indicating that the internal composition may include exotic states of matter, such as hyperons or quark matter, which are not accounted for in simpler models.
Furthermore, the study highlights how the Rastall parameter (λ) influences the mass-radius relationship and the moment of inertia of NSs. This suggests that the internal structure of NSs is sensitive to modifications in gravity, which could lead to new insights into the fundamental physics governing dense matter. By exploring the effects of Rastall gravity, researchers can better understand how deviations from GR might manifest in extreme environments, such as those found in the cores of massive NSs.
Overall, the combination of anisotropic pressure and modified gravity theories like Rastall gravity provides a more comprehensive framework for modeling the internal structure of NSs. This could lead to improved predictions regarding their mass, radius, and moment of inertia, ultimately informing our understanding of the composition and behavior of matter under extreme conditions, which is essential for astrophysical applications and theoretical physics.