scholarly journals Probing the Nuclear Equation of State from the Existence of a ∼2.6 M⊙ Neutron Star: The GW190814 Puzzle

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 183
Author(s):  
Alkiviadis Kanakis-Pegios ◽  
Polychronis S. Koliogiannis ◽  
Charalampos C. Moustakidis
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Equation Of State ◽  
Speed Of Sound ◽  
Compact Object ◽  
Dense Matter ◽  
High Mass ◽  
Nuclear Equation Of State ◽  
Dense Nuclear Matter ◽  
Low Mass

On 14 August 2019, the LIGO/Virgo collaboration observed a compact object with mass ∼2.59−0.09+0.08M⊙, as a component of a system where the main companion was a black hole with mass ∼23M⊙. A scientific debate initiated concerning the identification of the low mass component, as it falls into the neutron star–black hole mass gap. The understanding of the nature of GW190814 event will offer rich information concerning open issues, the speed of sound and the possible phase transition into other degrees of freedom. In the present work, we made an effort to probe the nuclear equation of state along with the GW190814 event. Firstly, we examine possible constraints on the nuclear equation of state inferred from the consideration that the low mass companion is a slow or rapidly rotating neutron star. In this case, the role of the upper bounds on the speed of sound is revealed, in connection with the dense nuclear matter properties. Secondly, we systematically study the tidal deformability of a possible high mass candidate existing as an individual star or as a component one in a binary neutron star system. As the tidal deformability and radius are quantities very sensitive on the neutron star equation of state, they are excellent counters on dense matter properties. We conjecture that similar isolated neutron stars or systems may exist in the universe and their possible future observation will shed light on the maximum neutron star mass problem.

scholarly journals Speed of sound and quark confinement inside neutron stars

2020 ◽  
Vol 229 (22-23) ◽  
pp. 3651-3661
Author(s):  
Michał Marczenko
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Speed Of Sound ◽  
Dense Matter ◽  
High Mass ◽  
Quark Confinement ◽  
Binary Neutron Star ◽  
Upper Limit ◽  
Unified Description

AbstractSeveral observations of high-mass neutron stars (NSs), as well as the first historic detection of the binary neutron star merger GW170817, have delivered stringent constraints on the equation of state (EoS) of cold and dense matter. Recent studies suggest that, in order to simultaneously accommodate a 2M⊙ NS and the upper limit on the compactness, the pressure has to swiftly increase with density and the corresponding speed of sound likely exceeds the conformal limit. In this work, we employ a unified description of hadron-quark matter, the hybrid quark-meson-nucleon (QMN) model, to investigate the EoS under NS conditions. We show that the dynamical confining mechanism of the model plays an important role in explaining the observed properties of NSs.

scholarly journals BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

2013 ◽  
Vol 776 (1) ◽  
pp. 47 ◽  
Author(s):  
M. Brett Deaton ◽  
Matthew D. Duez ◽  
Francois Foucart ◽  
Evan O'Connor ◽  
Christian D. Ott ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Equation Of State ◽  
High Spin ◽  
Nuclear Equation Of State ◽  
Low Mass

ERRATUM: “BLACK HOLE–NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE” (2013, ApJ, 776, 47)

2016 ◽  
Vol 824 (1) ◽  
pp. 62
Author(s):  
M. Brett Deaton ◽  
Matthew D. Duez ◽  
Francois Foucart ◽  
Evan O’Connor ◽  
Christian D. Ott ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Equation Of State ◽  
High Spin ◽  
Nuclear Equation Of State ◽  
Low Mass

scholarly journals A Machine Learning Approach For Classifying Low-mass X-ray Binaries Based On Their Compact Object Nature

2020 ◽  
Author(s):  
R Pattnaik ◽  
K Sharma ◽  
K Alabarta ◽  
D Altamirano ◽  
M Chakraborty ◽  
...  
Keyword(s):  
Machine Learning ◽  
Black Hole ◽  
Neutron Star ◽  
Binary Systems ◽  
Compact Object ◽  
X Ray ◽  
Average Accuracy ◽  
Machine Learning Approach ◽  
Low Mass ◽  
X Ray Binaries

Abstract Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether a LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5-25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87±13% in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g., SWIFT, XMM-Newton, XARM, ATHENA, NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.

scholarly journals Nuclear equation of state and neutron star cooling

2017 ◽  
Vol 26 (04) ◽  
pp. 1750015 ◽  
Author(s):  
Yeunhwan Lim ◽  
Chang Ho Hyun ◽  
Chang-Hwan Lee
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Thermal Evolution ◽  
Observation Data ◽  
Nuclear Equation Of State ◽  
The Core ◽  
Dense Nuclear Matter ◽  
Nuclear Models

In this paper, we investigate the cooling of neutron stars with relativistic and nonrelativistic models of dense nuclear matter. We focus on the effects of uncertainties originated from the nuclear models, the composition of elements in the envelope region, and the formation of superfluidity in the core and the crust of neutron stars. Discovery of [Formula: see text] neutron stars PSR J1614−2230 and PSR J0343[Formula: see text]0432 has triggered the revival of stiff nuclear equation of state at high densities. In the meantime, observation of a neutron star in Cassiopeia A for more than 10 years has provided us with very accurate data for the thermal evolution of neutron stars. Both mass and temperature of neutron stars depend critically on the equation of state of nuclear matter, so we first search for nuclear models that satisfy the constraints from mass and temperature simultaneously within a reasonable range. With selected models, we explore the effects of element composition in the envelope region, and the existence of superfluidity in the core and the crust of neutron stars. Due to uncertainty in the composition of particles in the envelope region, we obtain a range of cooling curves that can cover substantial region of observation data.

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.

scholarly journals Constraints on the speed of sound of dense nuclear matter through the tidal deformability of neutron stars

2021 ◽  
Vol 252 ◽  
pp. 05005
Author(s):  
Alkiviadis Kanakis-Pegios ◽  
Polychronis Koliogiannis ◽  
Charalampos Moustakidis
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Nuclear Matter ◽  
Speed Of Sound ◽  
Nuclear Physics ◽  
Equations Of State ◽  
Open Problems ◽  
Binary Neutron Star ◽  
Dense Nuclear Matter

One of the greatest interest and open problems in nuclear physics is the upper limit of the speed of sound in dense nuclear matter. Neutron stars, both in isolated and binary system cases, constitute a very promising natural laboratory for studying this kind of problem. This present work is based on one of our recent study, regarding the speed of sound and possible constraints that we can obtain from neutron stars. To be more specific, in the core of our study lies the examination of the speed of sound through the measured tidal deformability of a binary neutron star system (during the inspiral phase). The relation between the maximum neutron star mass scenario and the possible upper bound on the speed of sound is investigated. The approach that we used follows the contradiction between the recent observations of binary neutron star systems, in which the effective tidal deformability favors softer equations of state, while the high measured masses of isolated neutron stars favor stiffer equations of state. In our approach, we parametrized the stiffness of the equation of state by using the speed of sound. Moreover, we used the two recent observations of binary neutron star mergers from LIGO/VIRGO, so that we can impose robust constraints on the speed of sound. Furthermore, we postulate the kind of future measurements that could be helpful by imposing more stringent constraints on the equation of state.

scholarly journals Estimating the equation of state from measurements of neutron star radii with 5% accuracy

2018 ◽  
Vol 616 ◽  
pp. A105 ◽  
Author(s):  
M. Sieniawska ◽  
M. Bejger ◽  
B. Haskell
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Dense Matter ◽  
High Energy ◽  
High Mass ◽  
Recent Measurement ◽  
Accuracy Of Measurements ◽  
Observational Errors ◽  
Global Parameters

Context. Observations of heavy (⋍2 M⊙) neutron stars, such as PSR J1614−2230 and PSR J0348+0432, in addition to the recent measurement of tidal deformability from the binary neutron-star merger GW170817, place interesting constraints on theories of dense matter. Currently operating and future observatories, such as the Neutron star Interior Composition Explorer (NICER) and the Advanced Telescope for High ENergy Astrophysics (ATHENA), are expected to collect information on the global parameters of neutron stars, namely masses and radii, with an accuracy of a few percent. Such accuracy will allow for precise comparisons of measurements to models of compact objects and significantly improve our understanding of the physics of dense matter. Aims. The dense-matter equation of state is still largely unknown. We investigate how the accuracy of measurements expected from the NICER and ATHENA missions will improve our understanding of the dense-matter interior of neutron stars. Methods. We compared global parameters of stellar configurations obtained using three different equations of state: a reference (SLy4 EOS) and two piecewise polytropes manufactured to produce mass-radius relations indistinguishable from an observational point of view, i.e. within the predicted error of radius measurement. We assumed observational errors on the radius determination corresponding to the accuracies expected for the NICER and ATHENA missions. The effect of rotation was examined using high-precision numerical relativity computations. Because masses and rotational frequencies might be determined very precisely in the most optimistic scenario, only the influence of observational errors on radius measurements was investigated. Results. We show that ±5% errors in radius measurement lead to ~10% and ~40% accuracy in central parameter estimations for low-mass and high-mass neutron stars, respectively. Global parameters, such as oblateness and surface area, can be established with 8–10% accuracy, even if only compactness (instead of mass and radius) is measured. We also report on the range of tidal deformabilities corresponding to the estimated masses of GW170817 for the assumed uncertainty in radius.

scholarly journals The Formation and Evolution of Black-Hole Binaries

1996 ◽  
Vol 165 ◽  
pp. 93-103
Author(s):  
Roger W. Romani
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
High Mass ◽  
X Ray ◽  
Black Hole Binaries ◽  
Low Mass ◽  
Formation And Evolution ◽  
X Ray Binaries ◽  
Black Hole Candidates

The presence of accreting black holes (BH) among the X-ray binaries has been recognized for many years. Traditionally, Cyg X-1 and the handful of other candidates have been thought of as cousins of the HMXB neutron star systems. Recent studies of the soft X-ray transients such as A 0620-00 have, however, shown that the dynamical evidence makes these low-mass systems very strong black-hole candidates. Further, analysis of the eventual end-states of various high-mass X-ray binaries suggest that some could end as observable BH-pulsar binaries, although the first such system is yet to be discovered.

scholarly journals Neutron star-black hole mergers with a nuclear equation of state and neutrino cooling: Dependence in the binary parameters

2014 ◽  
Vol 90 (2) ◽  
Author(s):  
Francois Foucart ◽  
M. Brett Deaton ◽  
Matthew D. Duez ◽  
Evan O’Connor ◽  
Christian D. Ott ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Equation Of State ◽  
Nuclear Equation Of State
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