pulsars

Studying the Inner Depths of Pulsar Wind Nebulae Using IXPE X-Ray Polarization Data

Mar 24, 2023
Neutron stars are rapidly rotating dense balls of nuclear material formed from the gravitational collapse of the cores of giant stars. Generally, we cannot see them because they are very small and don’t emit much thermal (heat) radiation. But one special class of neutron stars, called pulsars, have jets of radiation that pass by Earth once per rotation, creating a lighthouse effect whereby they appear to us as pulsating stars (hence the name "pulsar"). Many models have been proposed to explain the nature of pulsar emissions. The most basic one is called the “rotation-powered” model, where particles accelerated along the pulsar's magnetic field lines are dragged and rotated around by the spin, powering the observed synchrotron radiation and exerting a torque on the pulsar that causes it to slow down over time (known as magnetic braking). While this model allows us to approximate some pulsar parameters, such as the strength of the surface magnetic field, details of the emission process are unaccounted for. Other plausible models have been proposed, which we'll be able to better constrain using data from the Imaging X-Ray Polarimetry Explorer (IXPE), a small-mission NASA satellite launched in December 2021.

What the nose shows: Black Widow systems and the fundamental nature of nuclear matter

Apr 22, 2021
Neutron stars are made of highly compressed material called degenerate matter, which is so dense it must be described using the laws of quantum mechanics. As a result, NSs should have a unique relationship between mass and radius, determined by an “equation of state” (EoS). An EoS is a thermodynamic description of the entwined properties of, for example, temperature, pressure, and volume. The steam in a pressure cooker can be described by an EoS; so can the interior of a star. For neutron star-like conditions only density matters, which results in a density-dependent EoS, P(rho). But because their material is in an exotic state not found anywhere on Earth, the EoS for neutron stars remains unknown.