Pulsars are some of the most mysterious objects in the universe. They are the tiny, incredibly dense remains of massive stars that exploded in powerful supernova explosions. Even though a pulsar is only about 20 kilometers wide, it can contain more mass than our Sun. Pulsars spin very fast, and some rotate hundreds of times every second. Because of this regular spinning, scientists often call them the most accurate natural clocks in the universe.
However, these cosmic clocks sometimes behave strangely. Instead of slowing down smoothly over time, a pulsar suddenly speeds up for a short time. This unexpected event is called a pulsar glitch. Scientists have been trying to understand why these glitches happen for nearly 50 years.
Now, a new study by Anantharaman and his research team has brought scientists one step closer to solving this mystery. Using one of the largest computer simulations ever created for neutron stars, the team discovered that glitches may happen because of a combination of superfluid matter, starquakes, and hidden vortex traps inside the star.
What Is a Pulsar Glitch?
A pulsar slowly loses energy as it spins, so its rotation gradually becomes slower over millions of years.
But sometimes, without any warning, the pulsar suddenly spins just a little bit faster. Although the increase is very small, modern telescopes are accurate enough to detect it.
This sudden increase in rotation speed is known as a glitch.
Scientists study these glitches because they reveal what is happening deep inside a neutron star—something we cannot see directly.
The Strange Material Inside a Neutron Star
The inside of a neutron star is very different from anything found on Earth.
Below its hard outer crust is a special type of matter called a superfluid. A superfluid is a liquid that can flow without any friction.
Instead of rotating like normal water, a superfluid spins by creating millions of tiny whirlpools called vortices.
These vortices store the star's rotational energy.
Many of them become stuck to the crystal structure inside the neutron star's crust. Scientists call this process pinning.
As the outer crust slowly loses speed, the superfluid inside keeps spinning faster. This creates stress between the two layers.
Eventually, many vortices suddenly break free together. They transfer some of their energy to the crust, causing the whole star to spin slightly faster.
This produces a pulsar glitch.
The Problem With Older Models
For many years, scientists believed that glitches happened only because of these escaping vortices.
Computer simulations supported this idea.
However, there was one major problem.
Earlier simulations could only handle around 1,000 vortices because calculating the motion of every vortex required enormous computing power.
Real neutron stars contain far more vortices than that.
Because of this limitation, older models assumed that vortices were spread evenly throughout the star. But real neutron stars are much more complicated.
This simple picture could not explain why different pulsars produce different kinds of glitches.
A Much Bigger Simulation
To solve this problem, the researchers used a faster computer method called the Barnes-Hut algorithm.
This allowed them to simulate 100,000 vortices, making the model much closer to real neutron stars.
With this improved simulation, scientists could study how vortices behave when they are not spread evenly across the star.
The results were very surprising.
Starquakes Create Hidden Traps
As a pulsar slows down, its solid crust comes under increasing pressure.
Eventually, the crust cracks in an event called a starquake.
A starquake is similar to an earthquake on Earth, but it happens on an extremely dense neutron star.
When the crust cracks, its crystal structure changes.
Some regions become much better at holding vortices than others.
These special regions are called vortex traps.
Instead of being spread evenly, many vortices collect inside these traps.
Over time, more and more vortices become trapped until they suddenly escape together.
Glitches Can Happen in Steps
Older theories suggested that a glitch should happen almost instantly.
But the new simulation tells a different story.
If several vortex traps release their vortices one after another, the glitch does not happen in a single jump.
Instead, the pulsar speeds up in small steps.
This creates what scientists call a staggered rise.
Some real pulsars have already shown signs of this step-like behavior, although current telescopes cannot always measure it clearly.
Future radio telescopes may be able to detect these tiny steps more accurately.
Why Different Pulsars Behave Differently
Not every pulsar glitches in the same way.
Some produce many small glitches.
Others produce fewer but much larger ones.
The new study helps explain this difference.
Older Pulsars
Older pulsars, such as the famous Vela Pulsar, have experienced many starquakes during their lifetime.
These repeated starquakes create many vortex traps throughout the crust.
As a result, glitches are strongly influenced by these trapped vortices.
Younger Pulsars
Younger pulsars behave differently.
One example is PSR J0537-6910.
In younger stars, new starquakes can create fresh vortex traps while also releasing vortices from older traps at the same time.
This can produce much larger glitches.
The simulations match what astronomers have observed in this pulsar.
Two Different Sizes of Glitches
Another interesting discovery involves the size of glitches.
Scientists have noticed that some pulsars produce two common glitch sizes instead of one.
This is called a bimodal distribution.
Older theories could not explain why this happens.
The new model provides a simple answer.
Small glitches happen when vortices escape naturally as the star slows down.
Large glitches happen when several vortex traps suddenly release their stored vortices together.
Because two different processes are involved, the pulsar naturally produces two preferred glitch sizes.
This matches observations of several real pulsars.
The Star Can Organize Itself
The researchers made another surprising discovery.
Even when vortices start out evenly distributed, they do not always stay that way.
As time passes, they naturally gather into large groups.
This means that neutron stars can develop complex internal structures on their own, even without new starquakes.
These hidden structures may affect how future glitches happen.
Why This Research Is Important
For many years, scientists argued about two main ideas.
One theory said glitches happen because of escaping vortices.
The other suggested that cracks in the crust, or starquakes, were responsible.
The new study shows that both ideas are correct.
Starquakes create vortex traps inside the crust.
These traps store vortices until they suddenly release them.
Together, these two processes can explain many features of pulsar glitches that older models could not.
What Happens Next?
Although this research is a major step forward, scientists still have more work to do.
Real neutron stars are even more complicated than the simulation.
Different layers inside the star may have different properties, magnetic fields may change how vortices move, and scientists still need more observations to test the model.
Another challenge is that many pulsars have produced only a small number of observed glitches, making it difficult to study their long-term behavior.
Fortunately, new telescopes such as the Square Kilometre Array (SKA) will observe pulsars with much greater accuracy. These powerful instruments are expected to detect many more glitches in the coming years.
Conclusion
This new research gives scientists one of the clearest explanations yet for why pulsars suddenly spin faster.
Instead of relying on a single process, the study shows that superfluid vortices, starquakes, and hidden vortex traps all work together. Large computer simulations of 100,000 vortices revealed that these hidden traps can create step-like glitches and even explain why some pulsars produce two common glitch sizes.
As better telescopes and more powerful computers become available, scientists are getting closer to fully understanding these mysterious cosmic clocks. Every new pulsar glitch brings us another clue about the strange and extreme physics hidden deep inside neutron stars, helping us unlock one of the universe's greatest mysteries.
Reference: Anantharaman Sekharipuram Viswanathan, Dipankar Bhattacharya, M. Ali Alpar, Erbil Gügercinoğlu, "Pulsar glitches in the presence of vortex traps", MNRAS, 2026. https://arxiv.org/abs/2607.20398
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