Research On Rapid Cooling Of The Central Compact Object In Cassiopeia A

Since Landau first proposed the theoretical model of neutron star(NS)in the1930 s,to the discovery of pulsars,one of the four major astronomical discoveries in the 1960 s,and to the booming development of astrophysics today,significant progress has been made in the study of NSs.From the initial radio signals to the current allwaveband observations and gravitational wave signal detection,we have more and more observation methods to understand NSs comprehensively and in detail.The central compact object(CCO)in Cassiopeia A(Cas A),which emits nonpulsating X-ray radiation,allows us to understand its surface temperature through observations.The results show that the surface temperature of Cas A is continuously decreasing,and its downward trend is significantly faster than the standard thermal evolution theory of NSs.Therefore,we believe that there may be a special cooling mechanism inside it,leading to such rapid cooling.According to mainstream research,there may be pairing phenomenon inside Cas A,which results in superfluidity affecting the thermal evolution of the NS,as well as the formation and breaking of Cooper pairs.This process can emit strong neutrino radiation,which may cause the rapid cooling of Cas A.Additionally,shortly after the birth of a NS,there is an r-mode instability window,during which the NS can maintain a higher temperature for a long time due to r-mode heating.When the r-mode instability window closes,the heating from r-mode stops and the star’s temperature will rapidly decrease,which is what we observe as the rapid cooling of Cas A.We will systematically introduce the theoretical models for these two mechanisms and use them to explain the rapid cooling of Cas A.A comparative analysis will be carried out,particularly to explain the significant differences between these two mechanisms on a long time scale.We fit the observation data from the past 20 years and found that both the r-mode heating shutdown and the PBF rapid cooling can explain the observed results well.However,on a longer time scale,the r-mode model predicts more significant deviations from a linear relationship in the temperature change of Cas A.Obtaining longer observation data of Cas A or discovering other CCO or young NSs can help to test these two models and understand the structure of NSs and their internal physical environment.