Spinning like crazy
Alessandro Papitto – INAF-OA Roma – Mercoledi 13 Marzo 2019 ore 11:00, Aula IB09
Neutron stars are so small and compact that they can spin extremely quickly. Pulsars that spin at a period of a few milliseconds are the fastest stars known. Their huge velocity makes them ideal probes to measure the state of ultradense matter and test the theory of General Relativity. Millisecond pulsars attain their very fast rotation during a Gyr-long phase of accretion of matter from a low mass companion star, which drives a bright X-ray emission. When the mass transfer stops magnetospheric pulsed emission powered by the star rotation – and observed preferentially in the radio and gamma-ray bands – sets in. In 2013, the discovery of a ‘transitional’ millisecond pulsar that swings between an accretion-powered X-ray pulsar regime and a rotationally-powered radio pulsar state on a time scale of a few weeks, or even shorter, proved this evolution. The incredibly rich phenomenology of transitional millisecond pulsars is a collection of the different possible outcomes of the interaction between the pulsar wind of particles and radiation and matter in an accretion disk. The observation of optical pulsations from one of these pulsars at the INAF Galileo Telescope is just the last unexpected discovery. It suggests a dwarf 100km sized pulsar wind nebula and opens a window to observe the relativistic pulsar wind close to the region where electrons are accelerated. I will review the recent success of transitional millisecond pulsars observations and try to address the many enigmas they posed.