Synopsis: Internal Magnetic Field Causes Neutron Star to Go Wobbly

An analysis of x-ray emission from a magnetar suggests that its huge magnetic field has distorted its shape, causing it to wobble.
Synopsis figure
L. Calçada/ESO

Magnetars, a type of neutron star, produce colossal external magnetic fields, with magnitudes as high as 1011 tesla (a billion times stronger than the most powerful magnets on Earth). Possible evidence of an even stronger internal field comes from recent x-ray observations of a particular magnetar. Writing in Physical Review Letters, the authors report detection of a time-varying x-ray signal and conclude that it indicates a wobble, or precession, in the magnetar’s rotation caused by an internal field of 1012 tesla.

The typical magnetar emits a strong beam of x rays, which we observe as pulses each time the compact object rotates. The most accepted explanation for this emission is that it arises from a huge polar magnetic field that originates—according to one theory—from an initial field that gets “wound up” during the stellar collapse that forms the neutron star. This scenario predicts that an even stronger magnetic field in the shape of a donut coils around the interior of the magnetar, but no measurements of this so-called toroidal field have previously been made.

Kazuo Makishima from the University of Tokyo in Japan and his colleagues have now captured a hint of the toroidal field. They analyzed data from the Japanese Suzaku satellite on the magnetar 4U 0142+61, which emits x-ray pulses every 8.7 seconds. To their surprise, the team found that the pulse arrival time in hard x rays was not constant—sometimes coming early, sometimes late. To explain this, they assumed that a strong toroidal field deforms the magnetar into a prolate shape, like a football, which wobbles as it spins. The hard x-ray data could be explained if the wobble frequency is a tiny fraction (1.6×10-4) less than the spin frequency. This wobbling motion might generate detectable gravitational waves. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

Astrophysics

Previous Synopsis

Materials Science

Sliding Sand

Read More »

Next Synopsis

Nuclear Physics

Element Z=117 Confirmed

Read More »

Related Articles

Synopsis: Galactic Spirals May Form Spontaneously
Astrophysics

Synopsis: Galactic Spirals May Form Spontaneously

Spiral galaxies could be transient, nonequilibrium structures originating from the collapse of clouds of matter interacting solely through self-gravity.   Read More »

Synopsis: Neutrino Probes of Long-Range Interactions
Particles and Fields

Synopsis: Neutrino Probes of Long-Range Interactions

Researchers place new limits on hypothetical interactions between neutrinos and large electron populations on galactic scales. Read More »

Synopsis: Black Holes Could Reveal New Ultralight Particles
Particles and Fields

Synopsis: Black Holes Could Reveal New Ultralight Particles

Gravitational-wave signals could contain clues to extremely low-mass particles predicted by extensions of the standard model of particle physics. Read More »

More Articles