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‘Weird science’ of neutron stars

Cassiopeia A and an artist's impression of a neutron star

Nebula Cassiopeia A, the remains of a massive star that exploded as a supernova. At it's heart is a neutron star (inset, artist's impression), where densities increase from the crust (orange) to the core (red) and finally to the core region where a "superfluid" exists (inner red section).

ASTRONOMERS HAVE GLIMPSED the inner workings of a neutron star and found a unique world where the physics can only be described as “weird.”

A neutron star is the extremely dense, collapsed core left behind from an exploding star, or supernova.

University of Alberta astronomer Craig Heinke’s team found that the neutron star’s core contains a superfluid … a friction-less liquid that could seemingly defy the laws of gravity.

“If you could put some of this superfluid in a jar it would flow up the walls of the container and over the edge,” said Heinke.

Heinke says the core of the neutron star also contains a superconductor, a perfect electrical conductor.

“An electric current in a superconductor never loses energy—it could keep circulating forever.”

Neutron stars contain the densest known matter that is directly observable. One teaspoon of neutron star material weighs six billion tonnes.

“Depending on their composition, superconductors created in laboratories on Earth stop working at anything warmer than -100 to -200 degrees Celsius,” says team member Wynn Ho of the University of Southampton. “In contrast, the incredible densities in neutron stars allow superconductivity at close to a billion degrees Celsius.”

Chandra X-ray telescope

Artist's impression of NASA's Chandra X-ray space telescope.

Cooling down

The discoveries were made when the researchers used NASA’s Chandra X-ray space telescope to investigate a sudden temperature drop on one particular neutron star 11,000 light years from Earth.

Heinke says this neutron star, known as Cassiopeia A, offered the researchers a great opportunity.

“It’s only 330 years old,” said Heinke. “We’ve got ringside seats to studying the life cycle of a neutron star from its collapse to its present, cooling off state.”

The researchers determined that the neutron star’s surface temperature is dropping because its core recently transformed into a superfluid state and is venting off heat in the form of neutrinos … sub-atomic particles that flood through the universe.

Here on Earth our bodies are constantly bombarded by neutrinos from space, with 100 billion neutrinos passing harmlessly though our eyes every second.

They also found that the neutron star’s core is a superconductor … the highest temperature (millions of degrees) superconductor known.

This research helps us to better understand the life cycles of stars, as well as the behaviour of matter at incredibly high densities.

Adapted from information issued by University of Alberta and NASA. Image credits: X-ray, NASA / CXC / UNAM / Ioffe / D. Page, P. Shternin et al.; optical, NASA / STScI; illustration, NASA / CXC / M. Weiss.

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