Even ‘Weakling’ Magnetars are Strong and Powerful


The name alone, “magnetar” elicits a magnificent, powerful and strong astronomical object, and most of these “magnetic stars” are whirling, X-ray blasting dynamos, shooting out strong bursts of energy. But there are some magnetars which seem to have a softer, quieter side, and are called soft gamma repeaters and anomalous X-ray pulsars. However, they might not be as soft as they appear. A team of astronomers using the several different space- and Earth-based observatories have found a supposed ‘weakling’ was only masking its superpowers. The new findings indicate the presence of a huge internal magnetic field in these seemingly less powerful pulsars, which is not matched by their surface magnetic field.

Magnetars are a type of neutron stars, which are the collapsed remains of massive, rapidly rotating stars. They collapses down to tiny cores, with the hot neutron liquid rising and falling from the center to the crust setting up a dynamo effect, creating that incredible magnetic field. Although they are on average only about 30km in diameter, a magnetar can have a magnetic field billions of times that of our Sun.

It was thought that dramatic flares and bursts of energy came from only the strong class of magnetars, but these same features have been observed emanating from a weakly magnetized, slowly rotating pulsar.

“We have now discovered bursts and flares, i.e. magnetar-like activity, from a new pulsar whose magnetic field is very low,” said Dr Silvia Zane, from UCL’s (University College London) Mullard Space Science Laboratory, and an author of the research.

The neutron star, SGR 0418+5729, was discovered on June 5, 2009 when the Fermi Gamma-ray Space Telescope detected bursts of gamma-rays from this object. Follow-up observations four days later with the Rossi X-Ray Timing Explorer (RXTE) showed that, in addition to sporadic X-ray bursts, the neutron star exhibits persistent X-ray emission with regular pulsations that indicate that the star has a rotational period of 9.1 seconds.

What makes SGR 0418 different from similar neutron stars is that, unlike those stars that are observed to be gradually rotating more slowly, continued monitoring of SGR 0418 over a span of 490 days has revealed no evidence that its rotation is decreasing.

“It is the very first time this has been observed and the discovery poses the question of where the powering mechanism is in this case. At this point, we are also interested in how many of the other normal, low field neutron stars that populate the galaxy can at some point wake up and manifest themselves as a flaring source,” said Zane.

The team of astronomers, led by Dr. Nanda Rea of Institut de Ciencies de l’Espai (ICE-CSIC, IEEC) in Barcelona, wonder how large an imbalance can be maintained between the surface and interior magnetic fields. SGR 0418 represents an important test case.

“If further observations by Chandra and other satellites push the surface magnetic field limit lower, then theorists may have to dig deeper for an explanation of this enigmatic object,” said Rea.

Sources: Chandra Blog, University College, London (via Eurekalert)

12 Replies to “Even ‘Weakling’ Magnetars are Strong and Powerful”

  1. The physics here is a bit puzzling. Large magnetic fields tend to extert a huge pressure within the material they pass through. It appears that these stars must have some form of dynamo action which increases the magnetic field to the point it bursts the outer crust (largely iron in a degenerate electron crystalline form) which must act as a ferromagnetic “bottle.”


  2. “They collapses down to tiny cores, with the hot neutron liquid rising and falling from the center to the crust setting up a dynamo effect, creating that incredible magnetic field.”

    Eh? That might not be right. Motion of the misleading as “hot neutron liquid’, would be neutrons, these particles are electrically neutral. The only way to generate the fields are electrons or the inner quark soup


    The Eurekalert source article (link above) states:

    Theoretical studies indicate that in magnetars the internal field is actually stronger than the surface field, a property which can deform the crust and propagate outwards. The decay of the magnetic field leads to the production of steady and bursting X-ray emission through the heating of the neutron star crust or the acceleration of particles.

  4. @SALACIOUS (What happened to the Hon. and B. Crumb parts?),

    According to the diagram featured in “The guts of a neutron star“, magnetic fields in neutron stars are probably generated by protons in the neutron superfluid forming a superconductor.

  5. The dynamo action obviously requires the motion of charged particles. So there must be a different phase of matter near the core. I am not sure of this, but this also seems to require that neutron crystalline material or a crust of degenerate iron must also have a high magnetic permeability “high mu,” so that lots of magenetic flux lines can be trapped within the neutron star body.


  6. The concept of elements as classifiable and discrete entities in a neutron star should be given a little bit more thought. With proton and neutron in close proximity and in constant flux, the definition of any element likely fails, so iron as a participant in any magnetic effect is eliminated. Ditto crystals. A hot neutron star with an active dynamo doesn’t support any type of crystal, except as a fleeting union of small bits. Even then, it still doesn’t fall into the definition of crystal – protons don’t come any closer than the nuclear binding force allows. Neutrons in an HCP crystalline matrix form in a thermally stable environment.

    A high spin ionized neutron star with enough heat to allow neutron thermal motion will flatten the sphere somewhat and create a donut of drag induced flow. It is that flow that creates the dynamo effect (just like the dynamo inside the earth) and powers the field. Once energy is pumped into the field, disturbances of any kind can make it oscillate and beam out jets. The energy loss should be measurable, but in a ‘weakling’ system it may not be, over the time period that we use for measurements.

  7. the magnetic fields in the interstellar medium ISM must too play a major role besides gravity in forming magnetars and neutron stars. IGM magnetic fields and gravity largely shapes superclusters. aligned charged magnetic particle motion flows of magnetars over time measurements too long for our observations, shape magnetars by the flow of the entire galaxy, which likely is shaped into a hypersphere black hole universe.

  8. Current neutron star theory believes a difference of 10 times in the strength of the magnetic field between the inner field and surface field, will cause bursts of x-rays and Gamma rays. The neutron star SGR0418+5729 shows an imbalance between 50 to 100 times difference in strength, indicating neutron stars have a far more intense internal magnetic field then the iron surface magnetic field model with new implications on how the most powerful magnets in the cosmos evolve. Dirac stated that only ONE MONOPOLE IN THE UNIVERSE is sufficient for the universe to be filled with charge and black hole hyperspheres of all sizes.

  9. The surface of neutron stars might be composed of a dense iron material compressed to degenerate electron pressures. So a cubic cm of the stuff might have 10^3 tons or more. This would be a pretty serious ferromagnetic materia, I should think. The material should hold a considerable magnetization flux.

    I can’t comment on the magnetic properties of a neutron crystal, fluid or gas. The magnetic properties of neutrons in either of these phases is not known to me.


  10. Visualizing a magnetic field of 10 gigateslas, such as possible within a magnetar, puts a new ‘spin’ on everything…. literally. The idea that an electron’s orbit can be compressed by a magnetic field is fascinating. “Atoms are deformed into long cylinders thinner than the quantum-relativistic wavelength of an electron – the Compton wavelength of the electron is 2.4263102175±33×10^?12 meters..” In a field of about 10^5 teslas atomic orbitals deform into rod shapes. At 10^10 teslas, a hydrogen atom becomes a spindle 200 times narrower than its normal diameter….

    Would a sphere, composed of aligned and magnetically compressed hydrogen atom’s, act essentially like a monopole magnetic structure?

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