Magnetic hot spots on neutron stars survive for millions of years
European Week of Astronomy and Space Science press release
RAS PR 18/14 (EWASS 10)
3 April 2018

A study of the evolution of magnetic fields inside neutron stars shows that instabilities can create intense magnetic hot spots that survive for millions of years, even after the star’s overall magnetic field has decayed significantly. The results will be presented by Dr Konstantinos Gourgouliatos of Durham University at the European Week of Astronomy and Space Science (EWASS) in Liverpool on Wednesday, 4th April.

When a massive star consumes its nuclear fuel and collapses under its own gravity in a supernova explosion, it can result in a neutron star. These very dense objects have a radius of about 10 kilometres and yet are 1.5 times more massive than the Sun. They have very strong magnetic fields and are rapid rotators, with some neutron stars spinning more than 100 times per second round their axis. Neutron stars are typically modelled with a magnetic field that has a north and south magnetic pole, like the Earth's. However, a simple ‘dipole’ model does not explain puzzling aspects of neutron stars, such as why some parts of their surface are much hotter than their average temperature. 

Gourgouliatos and Rainer Hollerbach, of the University of Leeds, used the ARC supercomputer at the University of Leeds to run numerical simulations to understand how complex structures form as the magnetic field evolves inside a neutron star.

Gourgouliatos explains: “A newborn neutron star does not rotate uniformly – various parts of it spin with different speeds. This winds up and stretches the magnetic field inside the star in a way that resembles a tight ball of yarn. Through the computer simulations, we found that a highly wound magnetic field is unstable. It spontaneously generates knots, which emerge from the surface of the neutron star and form spots where the magnetic field is much stronger than the large-scale field. These magnetic spots produce strong electric currents, which eventually release heat, in the same way heat is produced when an electric current flows in a resistor.”

The simulations show that it is possible to generate a magnetic spot with a radius of a few kilometres and a magnetic field strength in excess of 10 billion Tesla. The spot can last several million years, even if the total magnetic field of the neutron star has decayed.

The study may have wide implications for our understanding of neutron stars. Even neutron stars with weaker overall magnetic fields could still form very intense magnetic hot spots. This could explain the strange behaviour of some magnetars, for example the exotic SGR 0418+5729, which has an unusually low spin rate and a relatively weak large-scale magnetic field but erupts sporadically with high-energy radiation.

Further information

Magnetic axis drift and magnetic spot formation in neutron stars with toroidal fields, Gourgouliatos K. and Hollerbach, R., The Astrophysical Journal, Volume 852, Number 1, published 28 December 2017.

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Durham University Marketing and Communications Office
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Science contacts

Dr Konstantinos N. Gourgouliatos
Durham University
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Images and captions

Gourgouliatos 1

Fig. 1. A tightly wound-up magnetic field used as initial state in the simulation. 


Gourgouliatos 2

Fig. 2. The magnetic field structure after it has become unstable leading to the formation of knots and magnetic spots.

Notes for editors

The European Week of Astronomy and Space Science (EWASS 2018) will take place at the Arena and Conference Centre (ACC) in Liverpool from 3 - 6 April 2018. Bringing together around 1500 astronomers and space scientists, the conference is the largest professional astronomy and space science event in the UK for a decade and will see leading researchers from around the world presenting their latest work.

EWASS 2018 is a joint meeting of the European Astronomical Society and the Royal Astronomical Society. It incorporates the RAS National Astronomy Meeting (NAM), and includes the annual meeting of the UK Solar Physics (UKSP) group. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and Liverpool John Moores University (LJMU).

Liverpool John Moores University (LJMU) is one of the largest, most dynamic and forward-thinking universities in the UK, with a vibrant community of 25,000 students from over 100 countries world-wide, 2,500 staff and 250 degree courses. LJMU celebrated its 25th anniversary of becoming a university in 2017 and has launched a new five-year vision built around four key ‘pillars’ to deliver excellence in education; impactful research and scholarship; enhanced civic and global engagement; and an outstanding student experience.

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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The European Astronomical Society (EAS) promotes and advances astronomy in Europe. As an independent body, the EAS is able to act on matters that need to be handled at a European level on behalf of the European astronomical community. In its endeavours the EAS collaborates with affiliated national astronomical societies and also with pan-European research organisations and networks. Founded in 1990, the EAS is a society of individual members. All astronomers may join the society, irrespective of their field of research, or their country of work or origin. In addition, corporations, publishers and non-profit organisations can become organizational members of the EAS. The EAS, together with one of its affiliated societies, organises the annual European Week of Astronomy & Space Science (formerly known as JENAM) to enhance its links with national communities, to broaden connections between individual members and to promote European networks.

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STFC's Astronomy and Space Science programme provides support for a wide range of facilities, research groups and individuals in order to investigate some of the highest priority questions in astrophysics, cosmology and solar system science. STFC's astronomy and space science programme is delivered through grant funding for research activities, and also through support of technical activities at STFC's UK Astronomy Technology Centre and RAL Space at the Rutherford Appleton Laboratory. STFC also supports UK astronomy through the international European Southern Observatory.

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