Magnetars are the most magnetically-intense objects known in the Universe and now astrophysicists may have found one of these stellar husks being choked by a magnetic noose so much that its shape has been warped, causing it to wobble as it spins.
Spawned after a massive star goes supernova, magnetars are cousins of neutron stars (and, by extension, pulsars) — dense objects consisting primarily of degenerate neutron matter whose structure prevents itself from collapsing into a black hole. They are approximately 20 kilometers wide, yet more massive than our sun. This means that they have gargantuan densities — a thimbleful of magnetar material would have a mass of 100 million tons.
But density isn’t the only impressive thing about these objects. The magnetic field contained within the progenitor star is also squeezed into these tiny objects, taking our idea of magnetism to a whole new level.
Magnetic fields contained within these objects have been registered to a strength of 1011 Tesla, a billion times stronger than the strongest magnetic field that can be generated on Earth. However, it is thought there is an even stronger magnetic field wrapped as a torus — like a ring doughnut — around the magnetar’s equator that, until now, has been impossible to detect.
In new research published in the journal of Physical Review Letters, a magnetar called 4U 0142+61 has been studied by the Japanese Suzaku satellite, documenting the object’s rapid pulses of X-ray radiation. As the magnetar spins, strong beams of X-rays are generated at its poles. Like a lighthouse, these beams sweep past the Earth and are registered as pulses separated by 8.7 seconds.
Researchers led by Kazuo Makishima of the University of Tokyo noticed that the pulses from 4U 0142+61 were not consistent, however. Sometimes the pulses would appear early; at other times they’d appear late. Considering that pulses from “regular” pulsars are normally as precise as the most accurate atomic clocks on Earth, this particular magnetar is an oddity.
To explain this irregularity in X-ray pulses, the researchers think there is a very powerful toroidal magnetic field wrapped around the magnetar — measuring up to 1011 Tesla, a magnitude greater than the magnetar’s global magnetic field. The magnetar is therefore misshapen like a football oval, forcing the magnetar to wobble as it spins. The wobble has a period a fraction of the spin period, which would explain the strange X-ray pulse detection.
4U 0142+61′s wobble should also be generating gravitational waves — gravitational ripples through spacetime, carrying energy away from the spinning object — that could be detected in the future.
This research highlights the exotic nature of magnetars, a class of object that we are only just beginning to understand.
Source: American Physics Society