Could Quark Stars Explain Magnetars Strong Magnetic Field?

The magnetic field surrounding the mysterious magnetar
Credit:NASA

Magnetars are the violent, exotic cousins of the well known neutron star. They emit excessive amounts of gamma-rays, X-rays and possess a powerful magnetic field. Neutron stars also have very strong magnetic fields (although weak when compared with magnetars), conserving the magnetic field of the parent star before it exploded as a supernova. However, the huge magnetic field strength predicted from observations of magnetars is a mystery. Where do magnetars get their strong magnetic fields? According to new research, the answer could lie in the even more mysterious quark star…

It is well known that neutron stars have very strong magnetic fields. Neutron stars, born from supernovae, preserve the angular momentum and magnetism of the parent star. Therefore, neutron stars are extremely magnetic, often rapidly spinning bodies, ejecting powerful streams of radiation from their poles (seen from Earth as a pulsar should the collimated radiation sweep through our field of view). Sometimes, neutron stars don't behave as they should, ejecting copious amounts of X-rays and gamma-rays, exhibiting a very powerful magnetic field. These strange, violent entities are known as magnetars. As they are a fairly recent discovery, scientists are working hard to understand what magnetars are and how they acquired their strong magnetic field.

Denis Leahy, from the University of Calgary, Canada, presented a study on magnetars at a January 6th session at this week's AAS meeting in Long Beach, revealing the hypothetical "quark star" could explain what we are seeing. Quark stars are thought to be the next stage up from neutron stars; as gravitational forces overwhelm the structure of the neutron degenerate matter, quark matter (or strange matter) is the result. However, the formation of a quark star may have an important side effect. Colour ferromagnetism in color-flavour locking quark matter (the most dense form of quark matter) could be a viable mechanism for generating immensely powerful magnetic flux as observed in magnetars. Therefore, magnetars may be the consequence of very compressed quark matter.

These results were arrived at by computer simulation, how can we observe the effect of a quark star — or the "quark star phase" of a magnetar — in a supernova remnant? According to Leahy, the transition from neutron star to quark star could occur from days to thousands of years after the supernova event, depending on the conditions of the neutron star. And what would we see when this transition occurs? There should be a secondary flash of radiation from the neutron star after the supernova due to liberation of energy as the neutron structure collapses, possibly providing astronomers with an opportunity to "see" a magnetar being "switched on". Leahy also calculates that 1-in-10 supernovae should produce a magnetar remnant, so we have a pretty good chance at spotting the mechanism in action.

Written by Ian O'Neill

Universe Today