by Scientists may have unlocked the secret of the most extreme “dead stars” in the universe and the explanation is complex.
The team thinks that this “glitching” is caused by an insult of quantum tornadoes in the spin of a class of neutron stars called pulsars when it becomes entangled with its neighbors like the arms of a nearby cactus row, creating complex patterns and complicated.
“More than half a century has passed since the discovery of neutron stars, but why glitches occur is still not understood,” team member and Hiroshima University professor Muneto Nitta said in a statement. “So we proposed a model to explain this phenomenon.”
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A team of researchers looked at 533 observations of pulsars to solve the mystery of these glitches. They suggest glitches result from a “quantum vortex network” that aligns with power-law calculations, developing a model that does not require “additional tuning,” unlike previous neutron star glitch models.
Neutron star ‘glitches’ run deep
Neutron stars are born when massive stars die, run out of fuel for nuclear fusion and collapse under their own gravity. Its outer layers are blown away in massive supernova explosions. This leaves a stellar core of one to two times the mass of the sun, shrinking down to a diameter of about 12 miles (kilometers). That is small enough to fit in the average city on Earth.
The consequence of this catastrophe is that electrons and protons are pushed together, creating a sea of neutrons so dense that if a tablespoon of it were brought to Earth, it would be more than 1 billion tons, bigger than Mount Everest.
The downward pressure of stellar cores is also responsible for the rapid rotation of young neutron stars, with some speeds reaching up to 700 rotations per second. This is due to the conservation of angular momentum, which is like an ice skater on Earth pulling in their arms to increase the speed of their spin.
“Defunct” neutron stars or newborn “pulsars” appear to have a pulse because they shoot beams of radiation from their poles as they spin rapidly. The pulses brighten periodically when their beams point directly at Earth, giving them the appearance of a pulse (hence their name). This pulse can be compared to a cosmic “heartbeat” so precise that these young neutron stars can be used as cosmic stopwatches in so-called pulsar timing arrays to measure the timing of celestial events.
There is a win, though. Some neutron stars appear to “glitch” from time to time, briefly speeding up their rotation and the delivery of their pulses, which disrupts the regularity of their hearts. The cause of these glitches is shrouded in mystery.
Pulsar glitches appear to follow a similar pattern, or “power law,” as earthquakes on Earth. Just as low-magnitude earthquakes are more common than high-magnitude earthquakes, low-energy glitches occur more frequently for pulses than high-energy glitches and extremes.
Neutron star glitches have two prevailing mechanisms: star tremors and tiny quantum vortex “avalanches” that resemble microscopic hurricanes in the superfluid soup that makes up a neutron star’s interior.
Quantum vortices are generally accepted as an explanation over stellar ones because, while star tremors follow a power law like earthquakes, they struggle to account for all kinds of neutron star glitches. But, despite being more widely accepted, there is no correct explanation of what could cause a catastrophic flow of superfluid vortices that could reach the surface of a neutron star and increase its spin speed.
“In the standard case, researchers consider that a buffer of unpinned vortices could explain the origin of the glitches,” Nitta explains in the press release. “If there were no peeling, it means that the superfluid releases vortices one by one, allowing a smooth adjustment in the speed of rotation. There would be no exchanges and no glitches.”
Nitta added that the team’s model does not require an additional peeling mechanism. This model only considers a structure composed of two types of waves through the neutron star superfluid: a “P wave,” which is a fast-moving longitudinal wave, and a slower-moving “S wave.” cross wave.
“In this structure, all vortices are connected to each other in each cluster, so they cannot be released one by one,” continued Nitta. “Instead, the neutron star must release a large number of vortices at the same time. That is the main point of our model.”
Normal matter in neutron stars is drag
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The team’s model suggests that the superfluid core of a neutron star spins at a constant speed, but is pulled by the non-superfluid “normal fluid” component. The result is a slowing of the neutron star’s rotation speed through the emission of electromagnetic pulses and tiny ripples in space and time called gravitational waves.
Over time, the difference in speeds increases, causing the interior of a neutron star to eject superfluid jets, carrying angular momentum, speeding up the normal component, and causing an increase in rotation rates that we see as pulsar glitches.
The team suggests that the superfluid in neutron stars is divided into two types, which explains how these bubbles are born. The S-wave superfluid, which dominates the outer core of the neutron star, provides a relatively tame environment that supports the formation of vortices with integer, or “integer,” spins. However, in the inner core of a neutron star, the team believes that p-wave superfluidity prevails, creating extreme conditions that would favor half-integer spin.
That means that entering the largest p-wave inner core will split an integer spin vertex into two half-integers. This creates a redundant structure called “boojum” shaped like a cactus. As more half vortices are created and joined by boojums, the dynamics of the vortex clusters become increasingly complex. Imagine this is like cactus arms intertwining with nearby plant limbs, creating increasingly complex and complex patterns.
The team performed simulations that showed their model is very close to replicating the glitch energies of real-world neutron star glitches.
“Our argument, although simple, is very powerful. Although we cannot directly observe the excess p-wave inside, the logical consequence is the power-law behavior of the cluster sizes obtained from simulations ,” staff member and Nishogakusha University associate professor Shigehiro Yasui said. “Transferring this to a corresponding power-law distribution for glitch energy showed that it was consistent with the observations.”
“A neutron star is a very special case because the three fields of astrophysics, nuclear physics and condensed matter physics come together at one point,” concluded Yasui. “It’s very difficult to look directly because neutron stars are so far away. So we need to make a deep connection between the inner structure and some observational data from the neutron star.”
The team’s research is published in the journal Scientific Reports.
