Graduate Program in Physics at UFSC, Florianópolis

 THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar: 

  On The Spin Evolution of Isolated Pulsars 

Dr. Oliver Q. Hamil

Pós-doutorando – UFSC/FSC

 Abstract:

Isolated pulsars are a class of neutron stars that are spinning at high frequencies, and emit beams of electromagnetic radiation into space which appear like lighthouses to observers on earth. Observations of these objects span a few decades, and some of them have been documented with very high accuracy. Measurements of the pulsar rotational velocity Ω, and its time derivatives Ω and ̇ Ω, show that they slow down over time. The generally ̈ accepted explanation for the spin-down is that the pulsars behave like magnetic dipoles that lose energy in the form of electromagnetic radiation causing them to slow over time. This assumption of magnetic dipole radiation (MDR) leads to a general power law constructed from observation, Ω = ̇ −KΩ n is exactly 3 for MDR, but accurate observational measurements consistently yield values of 1.0 < n < 2.8. The reason for this discrepancy is unknown. In the present work we aim to improve understanding of the braking index through a two pronged investigation. We approach the problem by allowing for dynamical changes in the neutron star properties required in the braking index solution. We develop a frequency dependent model of the braking index that allows changing moment of inertia of the star, and changes in magnetic field properties in the MDR torque mechanism. For the first time, we have the opportunity to use physically realistic equations of state, along with state of the art computational codes to determine the dynamic properties of the neutron star needed in the modified braking index model. We probe the stars at constant baryonic rest masses ranging from 1.0M to 2.2M over a range of frequency spanning from zero to the Kepler (mass shedding) frequency for each star. We find that the braking index is sucseptible to changes in moment of inertia at very high frequencies, but unaffected in the lower frequency range where all of the reliably measured pulsars rotate. At low frequencies, however, we were able to again match the measured values by allowing for a change in the orientation of the magnetic moment of the dipole over time, in light of recent developments in the literature.

Date: 10/June/2016 – (friday) – Place: Sala 212 – Auditório do Departamento de Física- Time: 10h15min