Modelling pulsar timing noise

Lead Research Organisation: University of Southampton
Department Name: Sch of Mathematical Sciences

Abstract

Context: Pulsars - rotating neutron stars - are observed to gradually spin down, with the apparent loss in kinetic energy balancing a flux of electromagnetic and gravitational wave energy from the star. This spin down is smooth, but not perfectly so, with departures from a simple timing model being known as pulsar timing noise. The origin of this noise is not understood. The aim of this project is to develop mathematical models that describe this phenomenon.

Key objective and aims: the key objective is to build a model of a neutron star that incorporates the wide range of physical inputs that are likely to be important in this problem. The outputs of such a model would be compared against real timing noise and the model parameters adjusted so as to reproduce as accurately as possible the observed spin behaviour. In this way, the behaviour of fluids and solids in extremes of gravity, density and magnetic field would be probed, in a way that would simply not be possible in a terrestrial laboratory.

Novel methodology: the novel methodology lies in developing perturbation techniques to describe small departures from uniform rigid body spin-down, that include gravitational, elastic and magnetic forces. Then new numerical techniques to evolve the system on a computer would be developed, and used to explore the consequences of the model.

EPSRC research areas: The highly complex physics of neutron stars means that this project is relevant to multiple EPSRC research areas. Mathematical physics and Complexity science are the most obviously relevant areas, but there is also overlap with Cold atoms and molecules, Condensed matter: magnetism and magnetic materials, and Quantum fluids and solids.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1949172 Studentship EP/N509747/1 28/09/2017 30/09/2020 Garvin Yim
 
Description 1, Gravitational waves (GWs) from transient mountains caused by pulsar glitches

A pulsar is a neutron star (NS) that spins rapidly, emitting a flash of radiation with each full revolution (just like how you see light from a lighthouse). Therefore, the rate of flashing tells us something about the spin dynamics of the NS. A pulsar glitch is when the NS's spin frequency abruptly increases and then exponentially recovers back to, but never quite reaches, the pre-glitch spin frequency. There are a few models to explain this glitch recovery but we propose a new model whereby at the moment of the glitch, "mountains" are formed which causes the NS's spin frequency to decrease. Additionally, the newly-formed mountains creates a mass quadrupole on the NS so when it rotates, energy is lost as GWs. We take the optimistic view that the glitch recovery is solely due to this effect and calculate the strength and detectability of the resultant (transient) GWs. Our model predicts: transient GWs are marginally detectable with current 2nd-generation detectors; and transient GWs will be detectable in the 2030s with 3rd-generation detectors.

2, A physically-motivated model for timing noise

This part of the PhD project is still underway. Key findings will be reported at a more appropriate future date.
Exploitation Route 1, Gravitational waves (GWs) from transient mountains caused by pulsar glitches

The reason for this research is that a new model explaining pulsar glitch recoveries could be created with an independent test via GW observations. Currently, there are ongoing searches for transient GWs after pulsar glitches but so far, no transient GWs have been detected (which was predicted by our model). As detector sensitivities improve, there will be a higher chance to see these transient GWs and when we do see them, this theoretical model could explain the observations.

2, A physically-motivated model for timing noise

Not yet applicable.
Sectors Other