For more than 20 years, astronomers have been puzzled by the amazing pattern of bright, evenly spaced lines in radio waves from the Crab Pulsar, a dense supernova remnant recorded by Chinese and Japanese astronomers in 1054.
In 2024, an astronomer at the University of Kansas proposed a solution that explains the size of this unusual “zebra” pattern. Now, through pure analysis, he has shown that the lens of gravity is the last missing element needed to fully explain this phenomenon.
“Gravitational forces change the shape of space-time,” said Mikhail Medvedev, a KU professor of physics and astronomy, who will present his findings at the 2026 American Physical Society World Congress of Physics to be held March 15-20 at the Colorado Convention Center in Denver.
A related paper, accepted by the peer-reviewed Journal of Plasma Physics, is currently available at the first publication site arXiv.
“Light doesn’t travel in a straight line in gravity because space itself is curved,” he said. “What would be straight in a flat time becomes curved in the presence of gravity. In that sense, gravity acts like a lens in the curved time of space.”
Gravity and Plasma form a Unique Cosmic Tug-of-War
Although gravitational lensing is well known in the study of black holes, Medvedev says this is the first observed case where gravity and plasma work together to create a visible signal in space.
“In black hole images, gravity alone creates the structure,” he said. “In the Crab Pulsar, gravity and plasma work together. This represents the first real-world application of this combined effect.”
The Crab Pulsar is located in the center of the Crab Nebula in the Perseus Arm of the Milky Way, about 6,500 light-years from Earth. Its relatively close proximity makes it an important object for studying neutron stars, supernova remnants and nebulae.
An amazing brand unlike any other Pulsar
Medvedev describes the pulsar signal as very unusual. Instead of a continuous beam like sunlight, which spreads evenly across all colors, the Crab Pulsar produces distinct, separate bands.
“There is a strange pattern in Pulsar’s spectrum,” Medvedev said. “Unlike the usual broad spectrum – like sunlight, with many continuous colors – “Crab’s high-frequency inter-pulse shows unusual bands. If it was a rainbow, it was as if only certain ‘colours’ appeared, with nothing in between.”
Many pulsars emit radio waves that are noisy and spread across the spectrum. The Crab Pulsar stands apart in clear lines separated by total darkness.
“The lines are completely different and there is complete darkness between them,” said Medvedev. “There’s a bright band, then nothing, a bright band, nothing. There’s no other pulsar that shows this kind of striation. That uniqueness made the Crab Pulsar particularly interesting — and challenging — to understand.”
Gravity Gives a Weakening Fragment
Earlier versions of Medvedev’s model could produce a pattern of stripes, but they failed to match the strong differences seen in actual observations. His research has shown that the plasma around the pulsar bends and scatters the electromagnetic waves alternately, helping to create the pattern.
Now, by incorporating Einstein’s theory of gravity into this picture, he accounts for the missing difference.
“The previous theoretical model could produce structures, but not with the difference observed. The inclusion of gravity provides the missing part,” Medvedev said. “The plasma of the pulsar’s magnetosphere can be considered a lens – but a lens that distorts the focus. Gravity, on the other hand, acts as a focusing lens. The plasma tends to scatter light rays to the side; gravity pulls them inward.
Disruptive Techniques Produce Zebra Veins
The interaction between plasma and gravity creates multiple paths for pulsar radio waves. When these paths are aligned, the waves can reinforce or cancel each other, creating patterns of light and dark bands.
The KU researcher said that the combination of unfocused magnetospheric plasma and focused magnetic fields creates the in-phase and out-of-phase interference bands of radio waves that appear as stripes in the Crab Pulsar.
“By symmetry, there are at least two such paths for light,” he said. “When two parallel paths bring light to the observer, they form an interferometer. The signals overlap. At some frequencies, they reinforce each other (in phase), producing bright bands. At others, they cancel (out of phase), producing darkness. That is the source of the interference pattern.”
A New Tool for Studying Neutron Stars
Medvedev believes that the basic pattern of zebra crossings is now largely understood, although further improvements could improve accuracy.
Medvedev said: “There seems to be a little more physics needed to describe the veins qualitatively. “In general, there may be improvements. For example, current therapy involves gravity in a stable, low-intensity mode. The pulsar is still rotating, and including the effects of rotation can produce many changes, although not qualitative ones.”
The new model could give scientists a powerful way to study rotating gravitational systems and better understand pulsars, which are often difficult to see with the naked eye. It can also help map how matter is distributed around neutron stars and even shed light on their internal structure through their gravitational effects.
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