The exotic Magnetar

Magnetar in the very rich and young star cluster Westerlund 1 at 16 000 light-years away in the southern constellation of Ara (the Altar) Credit: ESO/L. Calçada

A magnetar is a type of neutron star with an extremely powerful magnetic field. But firstly what is a neutron star? This is a is the collapsed core of a large star, of about 10 to 29 solar masses, and they are the densest stars known to exist since they have a typical diameter of about 10 kilometres but having masses of about twice that of the Sun.

They are the result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past the white dwarf star density to that of atomic nuclei. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons.

Magnetars too have small diameters, around 20 kilometres, with masses of about 2 to 3 that of the Sun. Magnetars are differentiated from other neutron stars by having even stronger magnetic fields, and rotating comparatively slowly, with most magnetars completing a rotation once every one to ten seconds, compared to less than one second for a typical neutron star.

The star core crashes inwards supercharging its magnetism, all stars have strong magnetic fields at their surfaces but if the star dies and it collapses, the same amount of magnetic field must be present but the surface area of the star is decreased, say by a factor of a thousand of ten thousand that means that magnetic field intensity must be increase by the same amount.

An artist conception of the SGR 1806 20 magnetar including magnetic field lines. Credit: NASA/GSFC

So as the supernova's core collapses the magnetic field strength keeps building, a magnetars have the strongest magnetic in the universe which can be a trillion times stronger than the earth field, for reference it could wipe out the information of a credit card at a distance of 160.000 kilometres or roughly the distance half way to the moon. 

When the magnetic field becomes too strong it deforms creating seismic events called starquakes eventually the crust breaks and slips under the stress, the crust of the star slip about a centimetre which creates quakes millions of time stronger that the ones on our planet. The magnetic field is couple with the matter in it so when the crust slip so does the magnetic field launching a powerful blast of energy.

One such explosion was felt over here on earth on 2004, SGR 80620 180620 unleashed a starquake at a distance of 50.000 light years away creating a powerful gamma ray flare emission if this would have been close to earth it could be harmful to life, similar quakes were also recorded too on in 1979 and 1998. Giant stars with the potential to form magnetars still exists within our universe as of today we know of 23 magnetars. 

Animation of Magnetar SGR 1806-20 Credit: NASA/GSFC

Sources: Wikipedia, NASA, ESO