Warm noodles help hot, angry neutron stars cool down

Neutron stars are the angry ghosts of giant stars: hot, swirling cores of exotic species matter left behind after Supernovas. Like thermos flasks filled with hot noodle soup, it takes eons to cool down. But now the researchers believe they know how these stars do it: with a huge portion of pasta.

No, these ultra-dense star bodies are not filled with spaghetti. Instead, neutron stars cool down by releasing ethereal particles known as Neutrinos. And the new study shows they do this job thanks to an intermediate type of matter known as core noodles, a wavy, coiled material in which atoms are almost, but not quite, pulverized. This nuclear noodle structure creates sparse regions within the stars, allowing neutrinos and heat a way out.

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Trapped heat

A teaspoon of matter scraped off the surface of a neutron star would weigh billions of tons, more than any person on earth combined. This density helps them store heat very well. And while our sun, which is considered a yellow dwarf star, gives off most of its heat in the form of light, particles of light generated in a neutron star rarely make it to the surface to escape. Yet these angry undead stars – each the size of an American city – eventually calm down, mostly through the emission of neutrinos.

To understand how they cool off, researchers published a new study October 6 in the journal Physical examination C., took a closer look at the matter in neutron stars.

Ordinary stars are made of conventional matter or Atom: tiny spheres of protons and neutrons surrounded by relatively large swirling clouds of electrons. The interior of the neutron stars is now so dense that the atomic structure collapses and a huge ocean of so-called nuclear matter is created. Outside of neutron stars, nuclear matter refers to the material in atomic nuclei, dense spheres of protons and neutrons. And it’s subject to complex rules that scientists still don’t fully understand

Pasta is what lies between conventional matter and nuclear matter.

“Pasta is an intermediate step between nuclear matter and conventional matter,” said study co-author Charles Horowitz, a physicist at Illinois State University. Eventually, they start to touch, “Horowitz told Live Science. “And when they start touching, strange things happen.”

At some point the pressure rises so much that the structure of conventional matter completely breaks down into undifferentiated nuclear liquor. But just before that happens, there is a region with noodles.

In the noodle zone, Coulomb repulsion (the force that pushes charged particles apart) and nuclear attraction (the force that holds protons and neutrons together at very short distances) begin to work against each other. In regions where the nuclei touch but the atomic structure has not been completely broken down, the matter warps into complex shapes called “noodles”. Scientists have words for the different varieties of this material: gnocchi, waffle, lasagna, and anti-spaghetti.

“The shapes really look like pasta shapes,” said Horowitz.

Scientists have known for almost a decade that these noodles lie in neutron stars just below their crusts in the region where conventional matter transitions into bizarre, poorly understood nuclear material. And they also knew that neutrino emissions help cool neutron stars. The new study shows how the pasta helps release neutrinos.

Study leader Zidu Lin, a postdoctoral fellow at the University of Arizona, designed a series of large-scale computer simulations that showed how neutrinos could be formed in this eerie environment, Horowitz said.

The basic formula for producing a neutrino in a neutron star is simple: a neutron decays and transforms into a slightly lighter, lower-energy proton and an ultra-light neutrino. It’s a simple process that is known to take place elsewhere in space, including our sun. (At this very second, a huge stream of solar neutrinos rushes through your body.)

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But the conditions have to be right for this recipe to work. And in a neutron star, the conditions look wrong.

Neutron stars, as the name suggests, have many neutrons, all of which whiz around with high energy and lots of momentum. However, the neutrino recipe requires the creation of a low-energy proton with no momentum. But momentum cannot simply go away. It is always preserved. This is Isaac Newton’s first law of motion. (It’s also why you fly out the window when your car suddenly stops and you aren’t wearing a seat belt.)

Featherweight neutrinos cannot absorb the entire momentum of relatively bulky decaying neutrons. The only other place where there is momentum is the surroundings.

However, dense, rigid nuclear matter is a terrible place to lose momentum. It’s like driving a sports car into a thick slab of granite at high speed. The stone will barely move and the car will pancake as that momentum doesn’t have to go anywhere else. Simple models of neutron star emissions struggle to explain how nuclear matter can absorb enough momentum for neutrinos to escape.

Lin’s model showed that nuclear noodles solved much of this problem. These coiled, layered shapes have low density areas. And the noodles can compress and absorb the momentum in a wave motion. It’s like this granite wall is mounted on a spring that was compressed when the car crashed.

The researchers showed that neutrino emissions from kernel noodles in the core of a neutron star are likely far more efficient than neutrino emissions. That means pasta is likely to be responsible for much of the refrigeration.

That research, Horowitz said, suggests that neutron stars are cooling down more slowly than expected. That means they live longer. Stories of leisure need to be tweaked, he said, to explain their uncanny persistence in extreme heat for eons.

Originally published on Live Science.