Tuesday, October 23, 2012

Nuclear Pasta: Now Available at Your Nearest Supernova

At the end of their lives, massive stars can rapidly collapse onto their core and explode within a matter of seconds. As matter and particles rush toward the star's center, they pack together extremely tightly until they hit the limits at which nuclear forces flex their muscles.

This "bounce" against the nuclear forces leads to the massive explosion and shockwave whose remnants we can see with telescopes. During the bounce, there's some strange physics going on that remains to be fully understood.

Many scientists believe that the collapsing nuclei, protons, and neutrons from the star form strange formations during the bounce: nuclear pasta. The particles form spaghetti, meatballs, and lasagna density formations. Now, physicists can add a new pasta combination to the mix thanks to new research.

Stellini pasta image courtesy add1sun via flickr.


Jirina Stone from the University of Tennessee Knoxville and her student Helena Pais recently published their research on nuclear pasta in Physical Review Letters. Although other scientists had already discovered several pasta "phases," Pais and Stone started with an unprecedented blank slate.

Previous research had assumed that certain pasta shapes may exist in these particles' density distributions. For the latest research, however, Stone used a more general mathematical formalism that didn't assume specific shapes.

They found that their more general simulations did reveal the same pasta shapes as before such as meatballs and spaghetti rod shapes. But they found something unexpected as well: a new pasta shape.

Unfortunately, the new "cross-rod" shape doesn't have a pasta analogue name yet. You can see the general shape below. Might I suggest the "double bow-tie pasta" phase?

Density distributions for several pasta phases. Stone and Pais discovered the center "cross-rod" shape in their latest simulations. Image Credit: Helena Pais/Jirina Stone/American Physical Society

So how does this pasta form among nucleons (protons and neutrons), and what can it tell us about supernovae?

"There is this competition b/w two kinds of forces which act on the nucleons at the same time," Stone told Physics Central. "They don't know what to do."

Coulomb repulsion between the positively charged nucleons push them away from each other. But when two nucleons get close enough to each other, the nuclear force starts to take over and strongly pulls them together. These competing forces give rise to the strange pasta shapes.

Some estimates suggest that the pasta phases of matter account for 15-20 percent of the matter during a supernova's bounce. That's a significant chunk, and pasta may play a very important role during these cosmic explosions.

According to Stone, no current models fully capture the physics of a supernova explosion. Because there's so much physics behind these stellar explosions, scientists have had difficulty creating fully developed models. She hopes that this research may help better explain the physics behind supernovae, leading to more accurate models.

"It's one of the most diligently studied situations, but we don't have the answer," said Stone, referring to supernovae explosions.

More Information

Physics Synopsis of this research

Full research paper

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