Neutron Stars
Pulsar Winds
As a rapidly spinning young neutron star (a "pulsar") slows down, it deposits its enormous reservoir of rotational energy into its environment via a relativistic wind, producing an observable pulsar wind nebula (PWN). PWNe are a rich source of information. Most fundamentally, PWNe provide a direct probe of the high-energy processes through which a neutron star's considerable reservoir of rotational energy is eventually deposited into its environment. Secondly, because PWNe are close enough to be spatially resolved, they provide an excellent laboratory for studying the process through which a rotating compact object couples to its environment, a theme now also emerging in modeling of gamma-ray bursts and their afterglows. Finally, it is important to realize that the presence of a PWN unambiguously points to the presence of a central neutron star, even when the latter cannot be directly detected. PWNe are thus good signposts in the ongoing search for the youngest and most energetic neutron stars. We run a diverse X-ray, radio and optical program focused on using PWNe as probes of the interaction between pulsars and their environments. Through this work, we hope to provide a detailed physical basis for understanding the processes through which pulsars accelerate relativistic particles and interact with their surroundings.
For more information contact Bryan Gaensler , Shami Chatterjee
and Stephen Ng
Neutron Star Cooling
Neutron stars are macroscopic manifestations of processes that otherwise occur only in individual atomic nuclei. Formed hot in the core collapse that terminates the life of a massive star, they are supported against gravitational implosion by neutron degeneracy pressure. However, details of the interior structure of neutron stars remain poorly understood, largely due to our incomplete understanding of the strong interaction at ultrahigh densities. In the early stages of their lives, energy loss is dominated by neutrino emission. However, the neutrino production rate is highly dependent upon the structure of the interior. In the'normal' cooling scenario, neutrino production proceeds primarily via the modified Urca process. The residual heat diffuses from the core to the surface, manifesting itself as blackbody-like emission - modified by effects of any residual atmosphere - which peaks in the soft X-ray band. The rate at which the surface temperature declines depends critically upon the neutrino emission rate, and thus provides constraints on hadronic physics at high densities. We carry out X-ray observations of young neutron stars in order to explore their cooling properties and better understand the interior structure. Our results show that the standard cooling scenario is too slow to explain observations, and that enhanced neutrino cooling in the neutron star interiors is required.
For more information contact Bryan Gaensler , Shami Chatterjee
and Stephen Ng
Pulsar Timing Arrays
The extreme stability of millisecond pulsars provides a plethora of topics of interest to both theoretical and observational astronomers. Research into the use of pulsar timing arrays, such as the Parkes Pulsar Timing Array, is carried out in conjunction with the Australia Telescope National Facility and various international collaborators. We are mainly involved in searching for as yet unmodelled
signals in the timing data such as gravitational waves, clock errors and the effect of inaccuracies in the solar system planetary ephemeris.
For more information contact Bryan Gaensler
Scintillation
For pulsars, which are exceptionally compact sources, refraction and scattering lead to diverse and evolving interference patterns in their radio spectra. We use spectroscopic data on pulsars to investigate the structure of the ionised interstellar medium.
The Emission Mechanism Problem
SIfA staff have had a long standing interesting in radio and high energy emission mechanisms in neutron stars, radio wave propagation in pulsar magnetospheres, scintillation effects, pulsar electrodynamics, and electromagnetic processes in superstrong magnetic fields with application to magnetars.
For more information contact Don Melrose