In 2024, a theoretical astrophysicist at the University of Kansas proposed a solution that explained much of this unusual “zebra” pattern. Now, with a refined analysis, he has identified gravity’s lensing effect as the final missing ingredient needed to fully explain the phenomenon.

“Gravity changes the shape of spacetime,” said Mikhail Medvedev, KU professor of physics & astronomy, who will present his findings at the American Physical Society’s 2026 Global Physics Summit taking place March 15-20 at the Colorado Convention Center in Denver.

An associated paper, accepted by the peer-reviewed Journal of Plasma Physics, currently is available on the pre-print site arXiv.

“Light doesn’t travel in a straight line in a gravitational field because space itself is curved,” he said. “What would be straight in flat spacetime becomes curved in the presence of strong gravity. In that sense, gravity acts as a lens in curved spacetime.”

Gravity and Plasma Create a Unique Cosmic Tug-of-War

While gravitational lensing is well known in studies of black holes, Medvedev says this is the first observed case where both gravity and plasma work together to shape a signal detected from space.

“In black hole images, gravity alone shapes the structure,” he said. “In the Crab Pulsar, both gravity and plasma act together. This represents the first real-world application of this combined effect.”

The Crab Pulsar sits at the center of the Crab Nebula in the Perseus Arm of the Milky Way, about 6,500 light-years from Earth. Its relatively close distance and clear visibility make it a key object for studying neutron stars, supernova remnants, and nebulae.

A Strange Signal Unlike Any Other Pulsar

Medvedev describes the pulsar’s signal as highly unusual. Instead of a continuous spectrum like sunlight, which spreads smoothly across all colors, the Crab Pulsar produces distinct, separated bands.

“There’s a remarkable pattern in Pulsar’s spectrum,” Medvedev said. “Unlike ordinary broad spectra — such as sunlight, which contains a continuous range of colors — the Crab’s high-frequency inter-pulse shows discrete spectral bands. If it were a rainbow, it’s as if only specific ‘colors’ appear, with nothing in between.”

Most pulsars emit radio waves that are noisy and spread out across frequencies. The Crab Pulsar stands apart with sharply defined stripes separated by complete darkness.

“The stripes are absolutely distinct with complete darkness between them,” Medvedev said. “There’s a bright band, then nothing, bright band, nothing. No other pulsar shows this kind of striation. That uniqueness made the Crab Pulsar especially interesting — and challenging — to understand.”

Gravity Provides the Missing Piece

Earlier versions of Medvedev’s model could reproduce the striped pattern, but they failed to match the strong contrast seen in real observations. His research showed that plasma around the pulsar bends and spreads electromagnetic waves through diffraction, helping form the pattern.

Now, by adding Einstein’s theory of gravity into the model, he has accounted for the missing contrast.

“The previous theoretical model could reproduce stripes, but not with the observed contrast. The inclusion of gravity provides the missing piece,” Medvedev said. “The plasma in the pulsar’s magnetosphere can be thought of as a lens — but a defocusing lens. Gravity, by contrast, acts as a focusing lens. Plasma tends to spread light rays apart; gravity pulls them inward. When these two effects are superimposed, there are specific paths where they compensate each other.”

Interference Patterns Produce the Zebra Stripes

The interaction between plasma and gravity creates multiple paths for the pulsar’s radio waves. When these paths align, the waves can either reinforce or cancel each other, forming a pattern of bright and dark bands.

The KU researcher said the combination of a defocusing magnetospheric plasma and a focusing gravity create in-phase and out-of-phase interference bands of radio-wave intensity that appear as the Crab Pulsar’s zebra stripes.

“By symmetry, there are at least two such paths for the light,” he said. “When two nearly identical paths bring light to the observer, they form an interferometer. The signals combine. At some frequencies, they reinforce each other (in phase), producing bright bands. At others, they cancel (out of phase), producing darkness. That is the essence of the interference pattern.”

A New Tool for Studying Neutron Stars

Medvedev believes the core mechanism behind the zebra stripes is now largely understood, though further refinements may improve precision.

“There appears to be little additional physics required to explain the stripes qualitatively,” Medvedev said. “Quantitatively, there may be refinements. For example, the current treatment includes gravity in a static, lowest-order approximation. The pulsar is rotating, and including rotational effects could introduce quantitative changes, though not qualitative ones.”

This new model could give scientists a powerful way to study rotating gravitational systems and better understand pulsars, which are typically difficult to visualize directly. It may also help map how matter is distributed around neutron stars and even offer clues about their internal structure through their gravitational effects.

However, new research from the University of Colorado Boulder suggests this widely used sugar substitute may have serious downsides. Scientists found it can affect brain cells in ways that may increase the risk of stroke.

The findings were published in the Journal of Applied Physiology.

“Our study adds to the evidence suggesting that non-nutritive sweeteners that have generally been purported to be safe, may not come without negative health consequences,” said senior author Christopher DeSouza, professor of integrative physiology and director of the Integrative Vascular Biology Lab.

What Is Erythritol and Why Is It So Popular?

Erythritol was approved by the Food and Drug Administration in 2001. It is a sugar alcohol typically made by fermenting corn and is now used in hundreds of food products. It contains almost no calories, delivers about 80% of the sweetness of regular sugar, and has little effect on insulin levels. Because of this, it is commonly used by people trying to lose weight, manage blood sugar, or reduce carbohydrate intake.

Still, growing research is raising questions about its safety.

A large study of 4,000 people in the U.S. and Europe found that individuals with higher levels of erythritol in their blood were much more likely to experience a heart attack or stroke within three years.

Inside the Study: Effects on Brain Blood Vessels

To better understand why this risk may exist, DeSouza and lead author Auburn Berry, a graduate student in his lab, examined how erythritol affects cells.

In their experiment, researchers exposed human cells that line blood vessels in the brain to an amount of erythritol similar to what is found in a typical sugar-free drink for three hours.

The results showed several concerning changes. The cells produced much less nitric oxide, which helps blood vessels relax and widen, and more endothelin-1, which causes vessels to tighten. When exposed to thrombin, a substance that promotes clotting, the cells had a reduced ability to produce t-PA, a natural compound that helps break down clots. In addition, the treated cells generated higher levels of reactive oxygen species (ROS), also known as “free radicals,” which can damage cells, accelerate aging, and trigger inflammation.

Why These Changes Matter for Stroke Risk

“Big picture, if your vessels are more constricted and your ability to break down blood clots is lowered, your risk of stroke goes up,” said Berry. “Our research demonstrates not only that, but how erythritol has the potential to increase stroke risk.”

DeSouza pointed out that the study used only a single serving amount of erythritol. People who consume multiple servings daily could potentially face greater effects.

What Consumers Should Know

The researchers emphasize that their findings come from lab experiments on cells, not from studies in people, so more research is needed to confirm the risks in real-world settings.

Even so, DeSouza recommends paying closer attention to ingredient labels and watching for erythritol or “sugar alcohol.”

“Given the epidemiological study that inspired our work, and now our cellular findings, we believe it would be prudent for people to monitor their consumption of non-nutrient-sweeteners such as this one,” he said.

The fossil dates to about 17-18 million years ago and belongs to a newly identified species called Masripithecus. It is considered the closest known hominoid relative to the lineage that eventually led to all living apes, including humans. Scientists generally agree that the earliest apes (stem hominoids) first appeared in Afro-Arabia during the Oligocene Epoch more than 25 million years ago. These early apes later spread into Eurasia between about 14 and 16 million years ago during the Miocene. Still, the exact origin of modern apes, which include all living species and their last common ancestor, remains uncertain because fossils from this time are rare, scattered, and often difficult to interpret. This challenge is made worse by gaps in Africa’s fossil record, where most discoveries come from a limited number of locations, leaving large areas from this period unexplored.

Masripithecus moghraensis and Early Ape Diversity

Shorouq Al-Ashqar and colleagues describe the fossil, which was found in the Wadi Moghra region of northern Egypt and dates to around 17-18 million years ago. The species, named Masripithecus moghraensis, provides new insight into ape diversity during a key period when Afro-Arabia was becoming connected to Eurasia, allowing species to spread beyond Africa.

To determine how this species fits into the evolutionary history of humans, the researchers used a Bayesian “tip-dating” method. This approach combines anatomical features with fossil ages to estimate evolutionary relationships and divergence times. Their results indicate that Masripithecus is a stem hominoid closely related to the lineage that eventually gave rise to all modern apes.

New Clues to the Origins of Modern Apes

Based on their findings, the researchers suggest that modern apes may have originated in northern Afro-Arabia, the Levant, or the eastern Mediterranean. This challenges long-standing assumptions and highlights how much remains unknown about the early evolution of apes and humans.

This earthquake was triggered by a strike-slip fault, where two large sections of the Earth’s crust move horizontally past each other along a vertical fracture. To someone watching, it would appear as if the ground had split along a clear line, with each side being forced in opposite directions.

Previous studies based on seismic recordings suggested that earthquakes like this may involve a pulse-like rupture and slightly curved motion along the fault. However, those conclusions were based on instruments located far from the fault zone, meaning the observations were indirect.

Rare CCTV Footage Captures Fault Movement

In this case, a CCTV camera recorded the fault as it moved, creating a rare opportunity for researchers at Kyoto University to observe the rupture as it happened. (See video link at bottom of article.) This kind of direct visual evidence is extremely unusual in earthquake research.

Frame-by-Frame Analysis Reveals Extreme Speed

The research team used a method called pixel cross-correlation to examine the video frame by frame and measure how the ground shifted. Their findings show that the fault moved sideways by 2.5 meters in just 1.3 seconds, reaching a top speed of 3.2 meters per second.

While this amount of sideways movement is typical for strike-slip earthquakes, the very short duration of the motion stands out as a significant discovery.

“The brief duration of motion confirms a pulse-like rupture, characterized by a concentrated burst of slip propagating along the fault, much like a ripple traveling down a rug when flicked from one end,” says corresponding author Jesse Kearse.

Curved Fault Motion Challenges Assumptions

The analysis also revealed that the path of the slip was slightly curved. This matches earlier geological observations from faults around the world and suggests that fault movement is often not perfectly straight, as commonly assumed.

The study highlights the value of using video footage to monitor fault activity, offering a new way to study earthquakes in detail. Observations like these can improve understanding of how earthquakes unfold and help scientists better estimate the shaking that may occur during future large events.

“We did not anticipate that this video record would provide such a rich variety of detailed observations. Such kinematic data is critical for advancing our understanding of earthquake source physics,” says Kearse.

Next Steps in Earthquake Research

The researchers plan to build on these findings by using physics-based models to explore what controls fault behavior, using the new data revealed by this analysis.