Far out cosmology: neutron stars (Introduction)

by David Turell , Sunday, July 09, 2023, 18:00 (501 days ago) @ David Turell

Not fully understood:

https://knowablemagazine.org/article/physical-world/2023/probing-mysteries-neutron-star...

"Ever since neutron stars were discovered, researchers have been using their unusual properties to probe our universe. The superdense remnants of stellar explosions, neutron stars pack a mass greater than the Sun’s into a ball about as wide as San Francisco. A single cup of this star matter would weigh about as much as Mount Everest.

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"Stars power themselves by fusing the nuclei of lighter atoms into those of heavier atoms. But when stars run out of those lighter atoms, nuclear fusion stops and there is no longer an outward pressure to fight against the inward force of gravity. The core collapses and the star’s outer layer races inward. When this layer hits the dense core, it bounces off and explodes outward, producing a supernova. The dense core that remains afterward is a neutron star.

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"As some of the densest, highest-pressure objects in the universe, neutron stars might help us learn about what happens to matter at extremely high densities. Understanding their structure and the behavior of the neutron matter composing them is of paramount importance to physicists.

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"Matter that is below its Fermi temperature can obey remarkably universal laws. This universality means that, while we don’t have easy access to several-million-degree neutron star matter, we could learn about some of its behavior by experimenting with ultracold gases that can be created and manipulated in laboratory vacuum chambers on Earth, says theoretical astrophysicist James Lattimer of Stony Brook University in New York.

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"These ultracold atom clouds are actually closer to being a unitary gas than neutron star matter, so the analogy isn’t perfect. But it’s close enough that Lattimer has been able to take almost-unitary-gas measurements from the cold-atom clouds and apply them to neutron matter to refine some of the theoretical models that describe the internal workings of neutron stars. And experiments with cold atoms can help scientists develop theories about what physics might be at play in some unexplained neutron star phenomena.

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"In particular, Graber and other scientists are hoping to find clues to one of the biggest mysteries, called pulsar glitches. Generally, the regularly timed ticking of a pulsar “clock” is so reliable that its accuracy rivals that of atomic clocks. But not always: Sometimes, the pulsar’s rate of rotation increases abruptly, causing a glitch. Where that extra oomph comes from is unclear. The answer lies with how that matter moves around inside a neutron star.

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"Researchers are busy examining how other ultracold phenomena they regularly see in the lab can inspire new lines of research into the behavior of neutron stars. Recently, Graber and her colleagues outlined so many possibilities that they needed 125 pages to publish them all. In 2019, dozens of astronomers, nuclear physicists and ultracold atomic physicists from around the world gathered to discuss more of the surprising connections between their fields. Researchers are just beginning to test some of the ideas generated by these brainstorms.

"They’re also learning more from the stars themselves, says Pethick. “It’s an exciting field, because at the moment there are a lot of observations coming in.”

"With better telescopes and new methods to glean properties about a neutron star’s inscrutable interior, scientists can hope to find out just how far this analogy between cold atoms and neutron stars can be taken."

Comment: so astronomy becomes a big dance, analyzing what we can see and measure out there and doing mimicking experiments in the lab. My view is all of this exotic stuff exists so it must be required.