Scientists may have cracked the secret of the still-beating hearts of the most extreme “dead stars” in the universe, and the explanation is twisted.
The team believes that an avalanche of quantum tornadoes causes this “interference” in the spin of a class of neutron stars called pulsars when they tangle with their neighbors like the arms of a row of cacti in close proximity, creating twisted and complex patterns.
“More than half a century has passed since the discovery of neutron stars, but the mechanism by which the disturbances 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 propose the glitches to be the result of a “quantum vortex network” that is consistent with power-law calculations, thus developing a model that needs no “further tuning”, unlike previous models of neutron star glitches.
The “flaws” of neutron stars run deep
Neutron stars are born when massive stars die, run out of fuel for nuclear fusion, and collapse under their own gravity. Their outer layers are blown away in huge supernova explosions. This leaves a stellar core with one to two times the mass of the Sun, which is crushed to a diameter of approximately 12 miles (kilometers). That’s small enough to fit into an average city on Earth.
The consequence of this collapse is that electrons and protons are smashed 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 and outweigh Mount Everest.
The crushing 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 how skaters on Earth pull their arms to increase their spin speed.
Freshly “deceased” neutron stars or “pulsars” appear to pulsate because they shoot beams of radiation from their poles as they spin rapidly. Pulsars brighten periodically when their beams are pointed directly at Earth, making them appear to pulsate (hence their name). This pulsation can be likened to a cosmic “heartbeat” that is so precise that these young neutron stars can be used as cosmic stopwatches in so-called pulsar timing fields to measure the timing of celestial events.
However, there is a catch. Some neutron stars seem to occasionally get “stuck” and briefly speed up their rotation and pulse delivery, disrupting the regularity of their heartbeats. The cause of these glitches is shrouded in mystery.
Pulsar glitches appear to follow a similar pattern, or “power law,” to earthquakes on Earth. Just as low-magnitude earthquakes are more common than high-magnitude earthquakes, pulsars are more likely to experience low-energy disturbances than high-energy and extreme disturbances.
There are two predominant mechanisms involved in neutron star malfunctions: stellar shocks and tiny quantum vortex “avalanches” that form like microscopic hurricanes in the superfluid soup that makes up the neutron star’s interior.
Quantum vortices are generally more accepted as an explanation than starquakes, because while starquakes would obey a power law like earthquakes, they try to explain all types of neutron star perturbations. Despite widespread acceptance, there is no real explanation for what could trigger the catastrophic avalanche of superfluid vortices that can reach the surface of a neutron star and cause it to spin up.
“In a standard scenario, the researchers believe that an avalanche of unpinned vortices could explain the origin of the glitches,” Nitta explains in a press release. “If there was no pinning, this means that the superfluid releases the vortices one at a time, allowing for a smooth adjustment of the spin speed. There would be no avalanches or glitches.”
Nitta added that the team’s model does not need an additional attachment mechanism. This model only needs to consider a structure consisting of two types of waves rippling through the superfluid interior of a neutron star: a “P wave”, which is a fast-moving longitudinal wave, and an “S wave”, which is slower moving. transverse wave.
“In this structure, all the vortices in each cluster are interconnected, so they cannot be released one by one,” Nitta continued. “Instead, the neutron star must release a large number of vortices simultaneously. This is the key point of our model.”
Ordinary matter in neutron stars is a drag
The team’s model suggests that the neutron star’s superfluid core rotates at a constant rate, but the non-superfluid “ordinary” component drags along with it. The result is a slowing of the neutron star’s rotation rate by emissions of electromagnetic pulses and tiny ripples in space and time called gravitational waves.
Over time, the difference in velocities grows, resulting in the interior of the neutron star ejecting superfluid vortices, carrying angular momentum, accelerating the normal component and causing the spin rate increase we see as pulsar glitches.
The team suggests that the superfluid in neutron stars falls into two types, which explain how these vortices are born. The S-wave superfluids that dominate the outer core of a neutron star provide a relatively tame environment that favors the formation of vortices that have integer or “integer” spin. However, in the neutron star’s inner core, the team believes that p-wave superfluidity dominates, creating extreme conditions that favor half-whole spin vortices.
This means that an entire integer spin vortex would split into two half-integer vortices upon entering the p-wave-dominated inner core. This creates a superfluid structure called “boojum”, which is shaped like a cactus. As more half-vortices are created and joined by the boojum, the dynamics of the vortex clusters become increasingly complex. Think of it as the arms of cacti interweaving with the arms of a neighboring plant, creating increasingly complex and twisted patterns.
The team performed simulations that showed their model came very close to replicating the glitch energies of real neutron stars.
“Our argument, although simple, is very strong. Although we cannot directly observe the p-wave superfluid inside, a logical consequence of its existence is the power-law behavior of the cluster sizes obtained from simulations,” said team member and Nishogakusha University Associate Professor Shigehiro Yasui. “Converting this to the corresponding power-law distribution for the defect energies, it was shown to match 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,” Yasui concluded. “It is very difficult to observe directly because neutron stars exist 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.