scholarly journals Maximum baryon masses for static neutron stars in f(R) gravity

2021 ◽  
Author(s):  
A. V. Astashenok ◽  
Salvatore Capozziello ◽  
Sergei D. Odintsov ◽  
Vasilis K. Oikonomou
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Neutron Stars ◽  
Equations Of State ◽  
Gravitational Mass ◽  
Mass Limit ◽  
Mass Gap ◽  
Baryon Mass ◽  
Baryonic Mass ◽  
Lower Limits

Abstract We investigate the upper mass limit predictions of the baryonic mass for static neutron stars in the context of f(R) gravity. We use the most popular f(R) gravity model, namely the R2gravity, and calculate the maximum baryon mass of static neutron stars adopting several realistic equations of state and one ideal equation of state, namely that of causal limit. Our motivation is based on the fact that neutron stars with baryon masses larger than the maximum mass for static neutron star configurations inevitably collapse to black holes. Thus with our analysis, we want further to enlighten the predictions for the maximum baryon masses of static neutron stars in R2gravity, which, in turn, further strengthens our understanding of the mysterious mass-gap region. As we show, the baryon masses of most of the equations of states studied in this paper, lie in the lower limits of the mass-gap region M ∼ 2.5 − 5M⊙, but intriguingly enough, the highest value of the maximum baryon masses we found is of the order of M ∼ 3M⊙. This upper mass limit also appears as a maximum static neutron star gravitational mass limit in other contexts. Combining the two results which refer to baryon and gravitational masses, we point out that the gravitational mass of static neutron stars cannot be larger than three solar masses, while based on maximum baryon masses results of the present work, we can conspicuously state that it is highly likely the lower mass limits of astrophysical black holes in the range of M ∼ 2.5 − 3M⊙. This, in turn, implies that maximum neutron star masses in the context of R2gravity are likely to be in the lower limits of the range of M ∼ 2.4 − 3M⊙.

scholarly journals Recent LIGO-Virgo discoveries

2021 ◽  
pp. 2130010
Author(s):  
Maximiliano Isi
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Neutron Star ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Compact Objects ◽  
Tests Of General Relativity ◽  
Mass Gap ◽  
Cosmic History

The LIGO and Virgo gravitational-wave detectors carried out the first half of their third observing run from April through October 2019. During this period, they detected 39 new signals from the coalescence of black holes or neutron stars, more than quadrupling the total number of detected events. These detections included some unprecedented sources, like a pair of black holes with unequal masses (GW190412), a massive pair of neutron stars (GW190425), a black hole potentially in the supernova pair-instability mass gap (GW190521), and either the lightest black hole or the heaviest neutron star known to date (GW190814). Collectively, the full set of signals provided astrophysically valuable information about the distributions of compact objects and their evolution throughout cosmic history. It also enabled more constraining and diverse tests of general relativity, including new probes of the fundamental nature of black holes. This review summarizes the highlights of these results and their implications.

scholarly journals Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽  
2020 ◽  
Vol 6 (5) ◽  
pp. 63
Author(s):  
Hui Wang ◽  
Zhi-Fu Gao ◽  
Huan-Yu Jia ◽  
Na Wang ◽  
Xiang-Dong Li
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
General Expression ◽  
Equations Of State ◽  
Rotation Period ◽  
Ohmic Dissipation ◽  
Hartree Fock ◽  
Induction Equation ◽  
The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

scholarly journals Fundamental physics and the absence of sub-millisecond pulsars

2018 ◽  
Vol 620 ◽  
pp. A69 ◽  
Author(s):  
B. Haskell ◽  
J. L. Zdunik ◽  
M. Fortin ◽  
M. Bejger ◽  
R. Wijnands ◽  
...  
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Gravitational Wave ◽  
Equations Of State ◽  
Rotation Frequency ◽  
Hadronic Matter ◽  
Spin Distribution ◽  
Test Models ◽  
State Of Matter

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 ≈ 700 Hz, 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 ≈ 700 Hz 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 ≈ 700 Hz, as the lowest breakup frequency allowed by our causal equation of state is f ≈ 1200 Hz. A low-frequency cutoff, around f ≈ 800 Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M ≈ 2 M⊙. 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 ≈ 2 M⊙. 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.

scholarly journals Constraints on Microscopic and Phenomenological Equations of State of Dense Matter from GW170817

Universe ◽  
2019 ◽  
Vol 5 (10) ◽  
pp. 204 ◽  
Author(s):  
Domenico Logoteta ◽  
Ignazio Bombaci
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Equations Of State ◽  
Mean Field ◽  
Dense Matter ◽  
Neutron Star Matter ◽  
Field Approach ◽  
Relativistic Mean Field ◽  
Three Body ◽  
Good Agreement

We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the β -stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary’s component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data.

scholarly journals Relation between gravitational mass and baryonic mass for non-rotating and rapidly rotating neutron stars

2020 ◽  
Vol 15 (2) ◽  
Author(s):  
He Gao ◽  
Shun-Ke Ai ◽  
Zhou-Jian Cao ◽  
Bing Zhang ◽  
Zhen-Yu Zhu ◽  
...  
Keyword(s):  
Neutron Stars ◽  
Gravitational Mass ◽  
Baryonic Mass

Neutron Star Matter and Neutron Star Models

1974 ◽  
Vol 29 (6) ◽  
pp. 933-946
Author(s):  
H. Heintzmann ◽  
W. Hillebrandt ◽  
M. F. El Eid ◽  
E. R. Hilf
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
High Mass ◽  
Mass Limit ◽  
Neutron Star Matter ◽  
Density Region ◽  
Star Models ◽  
Boson Exchange ◽  
Realistic Interaction ◽  
General Relativistic

Various methods to study the ground state of neutron star matter are compared and the corresponding neutron star models are contrasted with each other. In the low density region ρ < 1014gr cm-3 the nuclear gas is treated here by means of a Thomas Fermi method and the nuclei are described by the droplet model of Myers and Swiatecki. For ρ > 1014 gr cm-3 both standard Brueckner theory with more realistic interaction (one-boson-exchange) potentials and the semiphenomenological theory of Fermi liquids (together with the standard Reid softcore potential) are applied to neutron star matter. It is shown that while the high mass limit of neutron stars is hardly affected, some properties of lowmass neutron stars such as their binding depend sensitively on these refinements. Various tentative (but unreliable) extensions of the equation of state into high density regime ρ > 1015 gr cm-3 are investigated and it is shown that the mass limit for heavy neutron stars lies around 2.5 solar masses. It is further shown that a third family of stable (hyperon) stars is not forbidden by general relativistic arguments if there is a phase transition at high densities.

scholarly journals The MAVERIC Survey: Variable Jet-accretion Coupling in Luminous Accreting Neutron Stars in Galactic Globular Clusters

2021 ◽  
Vol 923 (1) ◽  
pp. 88
Author(s):  
Teresa Panurach ◽  
Jay Strader ◽  
Arash Bahramian ◽  
Laura Chomiuk ◽  
James C. A. Miller-Jones ◽  
...  
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Radio Emission ◽  
Neutron Stars ◽  
Globular Clusters ◽  
Radio Continuum ◽  
X Rays ◽  
X Ray ◽  
Galactic Globular Clusters ◽  
X Ray Binaries

Abstract Accreting neutron stars in low-mass X-ray binaries show outflows—and sometimes jets—in the general manner of accreting black holes. However, the quantitative link between the accretion flow (traced by X-rays) and outflows and/or jets (traced by radio emission) is much less well understood for neutron stars than for black holes, other than the general observation that neutron stars are fainter in the radio at a given X-ray luminosity. We use data from the deep MAVERIC radio continuum survey of Galactic globular clusters for a systematic radio and X-ray study of six luminous (L X > 1034 erg s−1) persistent neutron star X-ray binaries in our survey, as well as two other transient systems also captured by our data. We find that these neutron star X-ray binaries show an even larger range in radio luminosity than previously observed. In particular, in quiescence at L X ∼ 3 × 1034 erg s−1, the confirmed neutron star binary GRS 1747–312 in Terzan 6 sits near the upper envelope of the black hole radio/X-ray correlation, and the persistently accreting neutron star systems AC 211 (in M15) and X1850–087 (in NGC 6712) show unusual radio variability and luminous radio emission. We interpret AC 211 as an obscured “Z source” that is accreting at close to the Eddington limit, while the properties of X1850–087 are difficult to explain, and motivate future coordinated radio and X-ray observations. Overall, our results show that neutron stars do not follow a single relation between inflow and outflow, and confirm that their accretion dynamics are more complex than for black holes.

scholarly journals Studying the parameters of the extended σ-ω model for neutron star matter

2020 ◽  
Vol 229 (22-23) ◽  
pp. 3615-3628
Author(s):  
David Alvarez-Castillo ◽  
Alexander Ayriyan ◽  
Gergely Gábor Barnaföldi ◽  
Hovik Grigorian ◽  
Péter Pósfay
Keyword(s):  
Neutron Star ◽  
Bayesian Analysis ◽  
Neutron Stars ◽  
Symmetry Energy ◽  
State Of The Art ◽  
Saturation Density ◽  
Mass Limit ◽  
Neutron Star Matter

AbstractIn this work we study the parameters of the extended σ-ω model for neutron star matter by a Bayesian analysis of state-of-the-art multi-messenger astronomy observations, namely mass, radius and tidal deformabilities. We have considered three parameters of the model, the Landau mass mL, the nuclear compressibility K0, and the value of the symmetry energy S0, all at saturation density n0. As a result, we are able to estimate the best values of the Landau mass of mL ≈ 0.73 GeV, whereas the values of K0 and S0 fall within already known empirical values. Furthermore, for neutron stars we find the most probable value of 13 km < R1.4 < 13.5 km and the upper mass limit of Mmax ≈ 2.2 M⊙.

scholarly journals Thermal properties of hot and dense matter: Influence of rapid rotation on protoneutron stars, hot neutron stars, and neutron star merger remnants

2021 ◽  
Vol 252 ◽  
pp. 05004
Author(s):  
Polychronis Koliogiannis ◽  
Charalampos Moustakidis
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Equations Of State ◽  
Interaction Model ◽  
Dense Matter ◽  
Baryon Density ◽  
Dense Nuclear Matter ◽  
Protoneutron Stars

The knowledge of the equation of state is a key ingredient for many dynamical phenomena that depend sensitively on the hot and dense nuclear matter, such as the formation of protoneutron stars and hot neutron stars. In order to accurately describe them, we construct equations of state at FInite temperature and entropy per baryon for matter with varying proton fractions. This procedure is based on the momentum dependent interaction model and state-of-the-art microscopic data. In addition, we investigate the role of thermal and rotation effects on microscopic and macroscopic properties of neutron stars, including the mass and radius, the frequency, the Kerr parameter, the central baryon density, etc. The latter is also connected to the hot and rapidly rotating remnant after neutron star merger. The interplay between these quantities and data from late observations of neutron stars, both isolated and in matter of merging, could provide useful insight and robust constraints on the equation of state of nuclear matter.

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