Population Synthesis of Accreting Neutron Stars

Neutron stars in a binary system accrete matter from their companion star. This accreted matter forms an accretion disk around the neutron stars that spin-up the period of rotation as well as increasing the temperature. This is due to nuclear reactions caused by the accreted matter on the surface and inside the crust of the neutron star. Within the databases of all known neutron star we can see the patterns that support these theories on their evolution, with the exception of a very small population that have cooler temperatures than expected. There are a few theories that could explain this. One theory is that this could be due to partially accreted crust that has not experienced all the nuclear reactions of a fully accreted crust. This theory is what we wanted to explore in our research. We created a computer program simulation of large populations of these accreting neutron stars to evaluate the temperature increase throughout this recycling process that brings these neutron stars a new phase of life. We observe the increase in mass, and spin period, and the weakening of the magnetic field that occurs as these stars transform over thousands of years in this miraculous partnership. We track the total mass accreted onto the surface of these neutron stars in order to calculate the heat emitted at various stages until it reaches a temperature of 1 MeV/nucleon of heat. We analyze the population to evaluate the number of years it takes for 90 % of accreting neutron stars to reach this temperature as a result of the nuclear reactions in their crust.