اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدDetermining the Equation of State of Cold, Dense Matter with X-ray Observations of Neutron Stars
89
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The unknown state of matter at ultra-high density, large proton/neutron number asymmetry, and low temperature is a major long-standing problem in modern physics. Neutron stars provide the only known setting in the Universe where matter in this regime can stably exist. Valuable information about the interior structure of neutron stars can be extracted via sensitive observations of their exteriors. There are several complementary techniques that require different combinations of high time resolution, superb spectral resolution, and high spatial resolution. In the upcoming decade and beyond, measurements of the masses and radii of an ensemble of neutron stars using these techniques, based on data from multiple proposed next-generation X-ray telescopes, can produce definitive empirical constraints on the allowed dense matter equation of state.
قيم البحث
اقرأ أيضاً
Equilibrium configurations of cold neutron stars near the minimum mass are studied, using the recent equation of state SLy, which describes in a unified, physically consistent manner, both the solid crust and the liquid core of neutron stars. Results
are compared with those obtained using an older FPS equation of state of cold catalyzed matter. The value of M_minsimeq 0.09M_sun depends very weakly on the equation of state of cold catalyzed matter: it is 0.094 M_sun for the SLy model, and 0.088 M_sun for the FPS one. Central density at M_min is significantly lower than the normal nuclear density: for the SLy equation of state we get central density 1.7 10^{14} g/cm^3, to be compared with 2.3 10^{14} g/cm^3 obtained for the FPS one. Even at M_min, neutron stars have a small liquid core of radius of about 4 km, containing some 2-3% of the stellar mass. Neutron stars with 0.09 M_sun <M<0.17 M_sun are bound with respect to dispersed configuration of the hydrogen gas, but are unbound with respect to dispersed Fe^56. The effect of uniform rotation on the minimum-mass configuration of cold neutron stars is studied. Rotation increases the value of M_min; at rotation period of 10 ms the minimum mass of neutron stars increases to 0.13 M_sun, and corresponds to the mass-shedding (Keplerian) configuration. In the case of the shortest observed rotation period of radio pulsars 1.56 ms, minimum mass of uniformly rotating cold neutron stars corresponds to the mass-shedding limit, and is found at 0.61 M_sun for the SLy EOS and 0.54 M_sun for the FPS EOS.
Recent developments in the theory of pure neutron matter and experiments concerning the symmetry energy of nuclear matter, coupled with recent measurements of high-mass neutron stars, now allow for relatively tight constraints on the equation of stat
e of dense matter. We review how these constraints are formulated and describe the implications they have for neutron stars and core-collapse supernovae. We also examine thermal properties of dense matter, which are important for supernovae and neutron star mergers, but which cannot be nearly as well constrained at this time by experiment. In addition, we consider the role of the equation of state in medium-energy heavy-ion collisions.
Neutron stars are the densest, directly observable stellar objects in the universe and serve as unique astrophysical laboratories to study the behavior of matter under extreme physical conditions. This book chapter is devoted to describing how electr
omagnetic observations, particularly at X-ray, optical and radio wavelengths, can be used to measure the mass and radius of neutron stars and how this leads to constraints on the equation of state of ultra-dense matter. Having accurate theoretical models to describe the astrophysical data is essential in this effort. We will review different methods to constrain neutron star masses and radii, discuss the main observational results and theoretical developments achieved over the past decade, and provide an outlook of how further progress can be made with new and upcoming ground-based and space-based observatories.
Apparent (radiation) radius of neutron star,R_infty, depends on the star gravitational mass in quite a different way than the standard coordinate radius in the Schwarzschild metric, R. We show that, for a broad set of equations of state of dense matt
er, R_infty(M_max) for the configurations with maximum allowable masses is very close to the absolute lower bound on R_infty at fixed M, resulting from the very definition of R_infty. Also, the value of R_infty at given M, corresponding to the maximum compactness (minimum R) of neutron star consistent with general relativity and condition v_sound<c, is only 0.6% higher than this absolute lower bound. Theoretical predictions for R_infty are compared with existing observational estimates of the apparent radii of neutron stars.
Theoretical models of the equation of state (EOS) of neutron-star matter (starting with the crust and ending at the densest region of the stellar core) are reviewed. Apart from a broad set of baryonic EOSs, strange quark matter, and even more exotic
(abnormal and Q-matter) EOSs are considered. Results of calculations of M_max for non-rotating neutron stars and exotic compact stars are reviewed, with particular emphasis on the dependence on the dense-matter EOS. Rapid rotation increases M_max, and this effect is studied for both neutron stars and exotic stars. Theoretical results are then confronted with measurements of masses of neutron stars in binaries, and the consequences of such a confrontation and their possible impact on the theory of dense matter are discussed.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
