Cooling of neutron stars and hybrid stars with a stiff hadronic EoS
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ooling of Neutron Stars and Hybrid Stars with a Stiff Hadronic EoS1 H. Grigoriana, b, D. Blaschkec, d, and D. N. Voskresenskye a
Laboratory for Information Technologies, JINR, Dubna, 141980 Russia b Department of Physics, Yerevan State University, Yerevan, Armenia cInstytut Fizyki Teoretycznej, Uniwersytet Wroc l awski, 50204 Wroc l aw, Poland d Bogoliubov Laboratory for Theoretical Physics, JINR, Dubna, 141980 Russia eNational Research Nuclear University (MEPhI), Moscow, 115409 Russia email: [email protected] Abstract—Within the “nuclear medium cooling” scenario of neutron stars all reliably known temperature – age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMUJ1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the masses of the pulsars PSR J16162230, PSR J03480432 and J007373039B and the companion of J17562251 provide indepen dent proof for the existence of neutron stars with masses in a broad range from 1.2 to 2M䉺. The values M > 2M䉺 call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about 2.4M䉺 would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without a readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of 2.426M䉺 for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass 1.674M䉺. DOI: 10.1134/S1063779615050111 1
1. INTRODUCTION
The cooling of compact stars (CS) is an observable phenomenon which is governed by the interplay of structure and composition (viz. the equation of state (EoS)) of CS with the transport properties and neutrino emissivities of the matter they are made of. It therefore allows, in principle, to explore the otherwise inaccessi ble physics of neutron star interiors. Until recently the complex situation with many poorly known parameters in the theory of CS cooling allowed for many possible scenarios due to the fact that the observational data on masses and radii as well as temperature and age of CS were not sufficiently constraining. Now the situation has tremendously improved with the observation of the segment of a cooling curve for the central compact object in the remnant of the his torical supernova Cassiopeia A [1, 2], thus with known age, temperature and rate of cooling followed over the past 13 years since its discovery [3–5]. In principle, the observed spectra and distance allow even for a rough constraint on mass and radius of the cooling CS [3, 6]. These data require a fast cooling process in the CS interior whi
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