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Nuclear Pasta: the Hardest Known Substance in the Universe

Last updated on July 13th, 2020 at 10:19 pm

On a clear night, you can see stars in the sky for millions of millions of miles. But not all stars are created equal. There are ones called neutron stars, and they’re the densest objects in the universe – next to black holes of course.

To give you some perspective, one teaspoon of a neutron star would weigh about as much as Mount Everest! Neutron stars are so unique that they form strange structures inside themselves that can resemble the pasta in your kitchen pantry. Scientists have named these structures “nuclear pasta”.

Introduction to Neutron Star

Neutron stars form when stars up to 20 times larger than our sun reach the end of their lives and explode into supernovas, leaving behind a small dense core. That core collapses under the force of gravity until almost all of the electrons and protons combine to form neutrons – hence the name neutron stars.

Scientists believe these strange pasta-like formations may limit how fast the stars can spin. Nuclear pasta is impossible to study directly on earth, so physicists use computer simulations to better understand it. The simulations allow researchers to study the motion of large numbers of neutrons and protons as they interact with each other, exposing these strange but interesting pasta shapes.

The study, titled “Elasticity of nuclear pasta”, was recently accepted for publication by the Physical Review Letters. The study was led by Matt Caplan, a Postdoctoral Fellow at the McGill Space Institute (MSI), and included members from the California Institute of Technology’s Walter Burke Institute for Theoretical Physics and Indiana University’s Nuclear Theory Center.

Cross-section of a neutron star. Credit: Wikipedia Commons/Robert Schulze

 

The Study of Nuclear Pasta

Compared to other classes of stars (with the exception of the hypothetical quark stars and strange stars) neutron stars are rather unique. Due to their intense gravity (which causes their outer layers to freeze) neutron stars are similar to Earth in that they have a solid crust surrounding a liquid inner core.  Below the crust, the high density causes the formation of material that has a strange structure.

In short, competing forces between the protons and neutrons inside a neutron star causes the material to assemble into strange shapes, such as long cylinders or flat planes commonly referred to as “lasagna” and “spaghetti” – hence the nickname “nuclear pasta”. While a fascinating subject of study, not much has been learned about this material or its mysterious structures.

As Caplan indicated in a recent McGill press release, “The strength of the neutron star crust, especially the bottom of the crust, is relevant to a large number of astrophysics problems, but isn’t well understood.”

To shed light on this, Caplan and his colleagues successfully ran the largest computer simulations ever conducted of neutron star crusts, and their study was the first to describe how these crusts break. These simulations, which consisted of Caplan and his team stretching and deforming the nuclear pasta to test its strength, required roughly 2 million hours of processor time.

Artist’s impression of a neutron star’s “nuclear pasta”, the strongest known material in the Universe. Credit: University of McGill/MSI

From this, they determined that their unique shapes, combined with the extreme density inside neutron stars, makes nuclear pasta is incredibly stiff. In fact, its strength even puts materials like graphene and carbon nanotubes to shame. This information could go a long way towards helping astronomers make sense of their observations of neutron stars.

And considering last year’s kilonova event, where two neutron stars collided, these results could also help astrophysicists in the research of gravitational waves. The study even suggests that neutron stars might generate small amounts of gravitational waves on their own. As Caplan indicated, knowing more about how materials behave inside a neutron star, scientists may be able to shed new light on the unusual physics that take place within them:

“A lot of interesting physics is going on here under extreme conditions and so understanding the physical properties of a neutron star is a way for scientists to test their theories and models. With this result, many problems need to be revisited. How large a mountain can you build on a neutron star before the crust breaks and it collapses? What will it look like? And most importantly, how can astronomers observe it?”

 

Video Courtesy – “ Inside Science

 

Reference- https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.132701

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Akshat Mishra is currently pursuing his doctoral degree in Physics from Lund University in Sweden. He feels the need to explore the depths of the not-so-dark universe while at the same time watch the quanta in action. Electronic Music is what puts him in the thinking zone.

Akshat Mishrahttps://www.scilynk.in/akshat-mishra
Akshat Mishra is currently pursuing his doctoral degree in Physics from Lund University in Sweden. He feels the need to explore the depths of the not-so-dark universe while at the same time watch the quanta in action. Electronic Music is what puts him in the thinking zone.

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