For more than two decades, a radio signal from the Crab pulsar has displayed perfectly spaced bands. This observation has long intrigued the astronomical community, as no other pulsar shows such regularity.
This pulsar corresponds to the collapsed core of a star that exploded in a supernova in the year 1054, located about 6,500 light-years from Earth. Its relative proximity and brightness make it a privileged object of study for examining stellar remnants.
Most radio emissions from pulsars are broad and poorly structured, not as sharp and banded as for the Crab pulsar.
Recently, work has lifted the veil on this singularity, attributing it to a particular combination between plasma properties and the effects of gravity. Mikhail Medvedev, from the University of Kansas, presented these results at a physics summit, and an article has been accepted in the
Journal of Plasma Physics.
In the pulsar's magnetosphere, plasma acts as a lens that broadens the propagation of radio waves, generating low-intensity zones. This phenomenon is well known in plasma physics, but here it interacts with an opposing force, gravity, which tends to concentrate the rays.
According to Einstein's theory of relativity, gravity curves spacetime and acts as a focusing lens. By superimposing itself on the dispersive effect of the plasma, it allows the formation of precise interferences, where certain frequencies are amplified and others canceled, producing the observed bands.
This discovery offers scientists a way to further explore neutron stars and other compact objects. The analysis of these signals allows estimating the matter distribution around these celestial bodies and even probing their interior thanks to gravitational effects.
Although the current model qualitatively explains the bands, adjustments are expected, for example by integrating the pulsar's rotation.