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Details of Grant 

EPSRC Reference: EP/T017325/1
Title: How do neutron stars spin?
Principal Investigator: Antonopoulou, Dr D
Other Investigators:
Researcher Co-Investigators:
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Department: Physics and Astronomy
Organisation: University of Manchester, The
Scheme: EPSRC Fellowship
Starts: 01 October 2020 Ends: 30 September 2024 Value (£): 445,445
EPSRC Research Topic Classifications:
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Panel History:
Panel DatePanel NameOutcome
03 Dec 2019 Stephen Hawking Fellowship Announced
21 Jan 2020 Stephen Hawking Fellowship Interview Panel 1 Announced
Summary on Grant Application Form
Neutron stars are the relics of stars which once had much more mass than our Sun, but not enough to collapse into a black hole. They can have twice the mass of our Sun but are as small as cities. This means that the density inside them is enormous and our familiar atoms get so squeezed that they decompose. As the name suggests, neutron stars are mostly made up of the neutral particles neutrons. In these conditions neutrons behave as a superfluid, an exotic type of fluid that flows without friction inside a very strong hard crust that forms the neutron star surface. Neutron stars are surrounded by a magnetosphere, like our planet, but their powerful magnetic fields are a trillion times stronger than the Earth's. Most neutron stars are discovered by the observations of radio pulses, which gave birth to the term pulsar. Pulsars rotate very fast and produce beams of emission that are only visible when they turn towards the Earth. By recording a series of pulses we can measure the rotation of pulsars and the way it changes with time. Our research focuses on using observations of pulsar rotation to understand the invisible neutron star interior and the exterior magnetosphere.

In general pulsar rotation is very stable, beating the best atomic clocks, and over time slowly decelerates in a highly predictable manner. This deceleration is the result of losing energy to the environment and its temporal evolution depends on the structure of the magnetic field and electric currents in the magnetosphere. For some pulsars the deceleration rate appears to switch between a few distinct values simultaneously with changes in the radio emission. We will study these correlated phenomena using high-sensitivity observations and use the results to uncover plasma flows and global conditions in the magnetosphere.

The slow deceleration of pulsar rotation is sometimes interrupted by very sudden violent accelerations, called glitches. Glitches are caused by the neutron superfluid pulsar interior. Due to its frictionless nature, parts of the superfluid interact so little with the solid neutron star crust that they do not decelerate as the rest of the star does and keep rotating at a higher speed. This situation cannot persist forever so occasionally, when the velocity difference becomes too large, the superfluid rotation abruptly decreases - and by means of angular momentum conservation, the solid crust accelerates. As friction is very weak, the remaining superfluid very slowly catches up with this fast change in crust rotation, which is observed as a recovery to pre-glitch rotation sometimes lasting many years. A theoretical model of this behaviour will be compared to dozens of recovery observations made by the Jodrell Bank Observatory and will allow us to access the microphysical nature of the weak superfluid friction at different depths (densities) inside neutron stars. This will shed light in the properties of matter in the extreme neutron star conditions, a state that is not accessible by any experiments conducted on Earth.

Glitches can be frequent in young neutron stars significantly affecting the evolution of their rotation over decades. To reveal their impact we will simulate pulsar rotation including a series of glitches over many years. We anticipate the results to help explain why glitches of the same pulsar differ but also to unveil the underlying decelerating mechanism.

Last, to use neutron stars as laboratories for such studies and other fundamental physics tests we need numerous high quality data. For this, we will design best observing practices in time for use in ambitious, highly-invested, future facilities such as the Square Kilometre Array.

Research will be carried out at the Jodrell Bank Centre of Astrophysics in Manchester, an ideal host as it maintains an extended database of timing data of over 800 data and its members have key roles in many current and future observatories.



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Organisation Website: http://www.man.ac.uk