Cooling of neutron stars and hybrid stars with a stiff hadronic EoS (original) (raw)
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Structure and Cooling of Neutron and Hybrid Stars
Exciting Interdisciplinary Physics, 2013
The study of neutron stars is a topic of central interest in the investigation of the properties of strongly compressed hadronic matter. Whereas in heavy-ion collisions the fireball, created in the collision zone, contains very hot matter, with varying density depending on the beam energy, neutron stars largely sample the region of cold and dense matter with the exception of the very short time period of the existence of the proto-neutron star. Therefore, neutron star physics, in addition to its general importance in astrophysics, is a crucial complement to heavy-ion physics in the study of strongly interacting matter. In the following, model approaches will be introduced to calculate properties of neutron stars that incorporate baryons and quarks. These approaches are also able to describe the state of matter over a wide range of temperatures and densities, which is essential if one wants to connect and correlate star observables and results from heavy-ion collisions. The effect of exotic particles and quark cores on neutron star properties will be considered. In addition to the gross properties of the stars like their masses and radii their expected inner composition is quite sensitive to the models used. The effect of the composition can be studied through the analysis of the cooling curve of the star. In addition, we consider the effect of rotation, as in this case the particle composition of the star can be modified quite drastically.
Confronting Neutron Star Cooling Theories with New Observations
The Astrophysical Journal, 2002
With the successful launch of Chandra and XMM/Newton X-ray space missions combined with the lower-energy band observations, we are now in the position where careful comparison of neutron star cooling theories with observations will make it possible to distinguish among various competing theories. For instance, the latest theoretical and observational developments appear to exclude both nucleon and kaon direct URCA cooling. In this way we can now have realistic hope for determining various important properties, such as the composition, degree of superfluidity, the equation of state and stellar radius. These developments should help us obtain better insight into the properties of dense matter.
Cooling rates of neutron stars and the young neutron star in the Cassiopeia A supernova remnant
Monthly Notices of the Royal Astronomical Society, 2011
We explore the thermal state of the neutron star in the Cassiopeia A supernova remnant using the recent result of Ho & Heinke (2009) that the thermal radiation of this star is well-described by a carbon atmosphere model and the emission comes from the entire stellar surface. Starting from neutron star cooling theory, we formulate a robust method to extract neutrino cooling rates of thermally relaxed stars at the neutrino cooling stage from observations of thermal surface radiation. We show how to compare these rates with the rates of standard candlesstars with non-superfluid nucleon cores cooling slowly via the modified Urca process. We find that the internal temperature of standard candles is a well-defined function of the stellar compactness parameter x = r g /R, irrespective of the equation of state of neutron star matter (R and r g are circumferential and gravitational radii, respectively). We demonstrate that the data on the Cassiopeia A neutron star can be explained in terms of three parameters: f ℓ , the neutrino cooling efficiency with respect to the standard candle; the compactness x; and the amount of light elements in the heat blanketing envelope. For an ordinary (iron) heat blanketing envelope or a low-mass (10 −13 M ⊙) carbon envelope, we find the efficiency f ℓ ∼ 1 (standard cooling) for x 0.5 and f ℓ ∼ 0.02 (slower cooling) for a maximum compactness x ≈ 0.7. A heat blanket containing the maximum mass (∼ 10 −8 M ⊙) of light elements increases f ℓ by a factor of 50. We also examine the (unlikely) possibility that the star is still thermally non-relaxed.
Minimal Cooling of Neutron Stars: A New Paradigm
The Astrophysical Journal Supplement Series, 2004
A new classification of neutron star cooling scenarios, involving either "minimal" cooling or "enhanced" cooling is proposed. The minimal cooling scenario replaces and extends the so-called standard cooling scenario to include neutrino emission from the Cooper pair breaking and formation process. This emission dominates that due to the modified Urca process for temperatures close to the critical temperature for superfluid pairing. Minimal cooling is distinguished from enhanced cooling by the absence of neutrino emission from any direct Urca process, due either to nucleons or to exotica such as hyperons, Bose condensates or deconfined quarks. Within the minimal cooling scenario, theoretical cooling models can be considered to be a four parameter family involving the equation of state (including various compositional possibilities) of dense matter, superfluid properties of dense matter, the composition of the neutron star envelope, and the mass of the neutron star. The consequences of minimal cooling are explored through extensive variations of these parameters. The results are compared with the inferred properties of thermally-emitting neutron stars in order to ascertain if enhanced cooling occurs in any of them.
Proton gaps and cooling of neutron stars with a stiff hadronic EoS
The recent measurements of the masses of the pulsar J00737-3039B and of the companion J1756-2251 and pulsars PSR J1614-2230, PSR J0348-0432 demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 M. To fulfill the constraint M max > 2M and to demonstrate the possibility of cooling scenarios for purely hadronic and further for hybrid stars we exploit the stiff DD2 hadronic equation of state producing a maximum neutron star mass M 2.43M. We show that the "nuclear medium cooling" scenario for neutron stars comfortably explains the whole set of cooling curves just by a variation of the star masses without the necessity for the occurrence of the direct Urca reaction. To describe the cooling data with the very stiff DD2 equation of state we select a proton gap profile from those exploited in the literature and allow for a variation of the effective pion gap controlling the efficiency of the medium modified Urca process. Fast cooling of young neutron stars like it is seen in the data for Cas A is explained with the DD2 equation of state when the following conditions are provided: the presence of an efficient medium modified Urca process, and a large proton gap at densities n < ∼ 2n 0 vanishing for n > ∼ (2.5 − 3)n 0 , where n 0 is the saturation nuclear density.
Cooling of hybrid neutron stars and hypothetical self-bound objects with superconducting quark cores
Astronomy and Astrophysics, 2001
We study the consequences of superconducting quark cores (with color-flavor-locked phase as representative example) for evolution of temperature profiles and the cooling curves in quark-hadron hybrid stars and in hypothetical self-bounded objects having no a hadron shell (quark core neutron stars). The quark gaps are varied from 0 to ∆q = 50 MeV. For hybrid stars we find time scales of 1 ÷ 5, 5 ÷ 10 and 50 ÷ 100 years for the formation of a quasistationary temperature distribution in the cases ∆q = 0, 0.1 MeV and > ∼ 1 MeV, respectively. These time scales are governed by the heat transport within quark cores for large diquark gaps (∆ > ∼ 1 MeV) and within the hadron shell for small diquark gaps (∆ < ∼ 0.1 MeV). For quark core neutron stars we find a time scale ≃ 300 years for the formation of a quasistationary temperature distribution in the case ∆ > ∼ 10 MeV and a very short one for ∆ < ∼ 1 MeV. If hot young compact objects will be observed they can be interpreted as manifestation of large gap color superconductivity. Depending on the size of the pairing gaps, the compact star takes different paths in the lg(Ts) vs. lg(t) diagram where Ts is the surface temperature. Compared to the corresponding hadronic model which well fits existing data the model for the hybrid neutron star (with a large diquark gap) shows too fast cooling. The same conclusion can be drawn for the corresponding self-bound objects.
Cooling of Neutron Stars with Color Superconducting Quark Cores
Nuclear Physics A, 2006
We show that within a recently developed nonlocal, chiral quark model the critical density for a phase transition to color superconducting quark matter under neutron star conditions can be low enough for these phases to occur in compact star configurations with masses below 1.3 M. We study the cooling of these objects in isolation for different values of the gravitational mass. Our equation of state (EoS) allows for two-flavor color superconductivity (2SC) quark matter with a large quark gap (∼100 MeV) for u and d quarks of two colors that coexists with normal quark matter within a mixed phase in the hybrid star interior. We argue that, if the phases with unpaired quarks were allowed, the corresponding hybrid stars would cool too fast. If they occurred for M < 1.3 M , as follows from our EoS, one could not appropriately describe the neutron star cooling data existing today. We discuss a "2SC + X" phase as a possibility for having all quarks paired in two-flavor quark matter under neutron star constraints, where the X gap is of the order of 10 keV-1 MeV. Density-independent gaps do not allow us to fit the cooling data. Only the presence of an X gap that decreases with increasing density would allow us to appropriately fit the data in a similar compact star mass interval to that following from a purely hadronic model. This scenario is suggested as an alternative explanation of the cooling data in the framework of a hybrid star model.
Nuclear Physics a, 2005
The impact of nuclear physics theories on cooling of isolated neutron stars is analyzed. Physical properties of neutron star matter important for cooling are reviewed such as composition, the equation of state, superfluidity of various baryon species, neutrino emission mechanisms. Theoretical results are compared with observations of thermal radiation from neutron stars. Current constraints on theoretical models of dense matter, derived from such a comparison, are formulated.
Cooling of young neutron stars and the Einstein X-ray observations
The Astrophysical Journal, 1981
Cooling of neutron stars is calculated using an exact stellar evolution code. The full general relativistic version of the stellar structure equations are solved, with the best physical input currently available. For neutron stars with a stiff equation of state, we find that the deviation from the isothermality in the interior is significant and that it takes at least a few thousand years to reach the isothermal state. By comparing the most recent theoretical and observational results, we conclude that for Cas A, SN1O06, and probably Tycho, "standard" cooling is inconsistent with the results from the Einstein Observatory, if neutron stars are assumed to be present in these objects. On the other hand, the "detection" points for RCW103 and the Crab are consistent with these theoretical results.