Dense Stars Deformed By Extreme Magnetic Forces

Scientists have found that dense stars known as magnetars are deformed by their extremely high magnetic fields, resulting in a wobbly orbit.

AsianScientist (Jun 25, 2014) – Using X-ray detectors on board the satellie Suzaku, Japanese researchers have determined that dense neutron stars known as magnetars are deformed by their extremely high magnetic fields, resulting in a wobbly orbit.

Neutron stars, the densest objects in the Universe, are as heavy as the Sun but have radii of only 10 km. A subclass of neutron stars called magnetars are thought to emit X-ray photons by consuming their huge magnetic energies, emissions which are detected as pulses as the magnetar rotates.

A research group in the Department of Physics of the Graduate School of Science at the University of Tokyo led by Professor Kazuo Makishima and collaborators at RIKEN has used JAXA’s Cosmic X-ray Satellite Suzaku, to observe the magnetar 4U 0142+61. The researchers observed that pulses of soft (low-energy) X-rays from this object are regularly emitted at its rotation period every 8.69 sec. However, hard (high-energy) X-ray pulses were not consistent, arriving about 15 hours before or after the soft X rays.

The researchers interpreted their findings to mean that the star is performing free precession, that is, wobbling away from its axis of symmetry. Furthermore, it also suggests that the magnetar is slightly elongated along the axis, forming a lemon shape. The implied deformation of this extremely dense and high-gravity object, in turn, suggests the presence of extremely strong toroidal (donut-shaped) magnetic fields, up to 1012 Tesla, residing inside this neutron star; a strength is close to the theoretically conceivable upper limit. The present work is the first to observationally estimate the strength of such internal magnetic fields of neutron stars.

The article can be found at: Makishima et al. (2014) Possible Evidence for Free Precession of a Strongly Magnetized Neutron Star in the Magnetar 4U 0142+61.

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Source: University of Tokyo.
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