Scientists may have discovered the secret to the still-beating hearts of the universe’s most extreme “dead stars,” and the explanation is twisted.
The team thinks that an avalanche of quantum tornadoes causes this “scratch” in the spin of a class of neutron stars called pulsars, when it tangles with its neighbors like the wings of a series of nearby cacti, creating twisted and complex patterns.
“More than half a century has passed since the discovery of neutron stars, but the mechanism of why the defects 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 defects. They propose defects as the result of a “quantum vortex network” that matches power-law calculations, thus developing a model that does not need “extra tuning”, unlike previous neutron star defect models.
Neutron star ‘flaws’ run deep
Neutron stars are born when massive stars die, running out of fuel for nuclear fusion and collapsing under their own gravity. Their outer layers explode in huge supernova explosions. This leaves a stellar core with one to two times the mass of the sun, compressed to a diameter of about 12 miles (kilometers). It is small enough to fit into the average city on Earth.
The consequence of this collapse is that electrons and protons are crushed together, creating a sea of neutrons so dense that if a tablespoon of it were brought to Earth, it would weigh more than 1 billion tons, weighing more than Mount Everest.
The destruction of stellar cores is also responsible for the rapid rotation of young neutron stars, with some reaching speeds of up to 700 revolutions per second. This is due to conservation of angular momentum, which is similar to an ice skater on Earth pulling on their arms to increase their rotational speed.
Newly “dead” neutron stars, or “pulsars,” appear to pulsate because as they spin rapidly, they blast beams of radiation from their poles. Pulsars periodically shine when their rays are directed directly at Earth, making them appear to pulsate (hence their name). This pulsation can be compared to a cosmic “heartbeat” that is so precise that these young neutron stars can be used as cosmic chronometers in so-called pulsar clusters to measure the timing of celestial events.
However, there is a catch. Some neutron stars appear to occasionally “fail,” briefly speeding up their spin and the dispersion of their pulses, thus disrupting the regularity of their heartbeats. The cause of these defects is shrouded in mystery.
Pulsar faults 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 faults occur more frequently for pulsars than high-energy, extreme faults.
There are two dominant mechanisms associated with neutron star failures: starquakes and tiny quantum vortex “avalanches” that form as microscopic hurricanes in the superfluid soup that makes up a neutron star’s interior.
Quantum vortices are generally more widely accepted as an explanation than starquakes because, while stars would follow a power law like earthquakes, they struggle to account for all kinds of neutron star defects. However, despite being more widely accepted, there is no real explanation of what could cause a catastrophic avalanche of superfluid vortices to reach the surface of a neutron star and cause it to spin up.
“In the standard scenario, the researchers consider that the avalanche of unprotected vortices could explain the origin of the faults,” explains Nitta in the press release. “If there were no pinning, that means the superfluid releases the vortices one at a time, allowing for a smooth adjustment in spin speed. There would be no avalanches and no glitches.”
Nitta added that the team’s model does not need an additional locking mechanism. This model should only consider a structure consisting of two types of waves flowing through the superfluid interior of a neutron star: a “P-wave”, which is a fast-moving longitudinal wave, and an “S-wave”, which is a slower motion. transverse wave.
“In this structure, all the vortices are connected to each other in each group, so they cannot be released one by one,” Nitta continued. “Instead, the neutron star must emit a large number of vortices at the same time. This is the key point of our model.”
The common matter in neutron stars is a drag
The team’s model suggests that the superfluid core of a neutron star rotates at a constant rate, but the “ordinary” non-superfluid component drags on top of it. The result is a slowing of the neutron star’s spin rate by the emission of electromagnetic pulses and tiny ripples in space and time called gravitational waves.
Over time, the change in velocity increases, resulting in the interior of the neutron star expelling superfluid vortices, carrying angular momentum, accelerating the ordinary component, and causing the increased spin rate we see as pulsar defects.
The team suggests that the superfluid in neutron stars is divided into two types, which explain how these vortices arise. The S-wave superfluids that dominate the neutron star’s outer core provide a relatively smooth environment that supports the formation of vortices that have integer or “integer” spins. However, in the inner core of a neutron star, the team thinks p-wave superfluidity dominates, creating extreme conditions that favor half-full spin vortices.
This means that an integer spin vortex would split into two half-integer vortices when it entered the p-wave-dominated inner core. This creates a superfluid structure called a “boojum” that is shaped like a cactus. As more half-vortices are created and connected through boojums, the dynamics of the vortex clusters becomes increasingly complex. Think of this as the wings of a cactus intertwining with the wings of a neighboring plant, creating increasingly intricate and twisted patterns.
The team performed simulations that showed their model comes very close to replicating the defect energies of real-world neutron star defects.
“Our argument, although simple, is very powerful. Although we cannot directly observe the p-wave superfluid inside, the logical consequence of its existence is the power-law behavior of the cluster sizes obtained from the simulations,” member of the team and Nishogakusha University. said Associate Professor Shigehiro Yasui. “Translating this into a corresponding power-law distribution of error energies showed that it matches the observations.”
“A neutron star is a very special situation because the three fields of astrophysics, nuclear physics and condensed matter physics meet at one point,” concluded Yasui. “It is very difficult to observe directly because neutron stars exist so far away from us. Therefore, we need to make a deep connection between the internal structure and some observational data from the neutron star.”
The team’s research is published in the journal Scientific Reports.