linlEDMONTON — A University of Alberta astronomer and his team have uncovered “weird” physics inside a neutron star in the Milky Way Galaxy.
Craig Heinke and his colleagues have discovered the core of the Cassiopeia A neutron star — the remains of a supernova — contains a frictionless superfluid that seems to defy gravity, as well as a superconductor that keeps electricity flowing without ever losing energy.
Scientists had long suggested this “weird state of matter” might exist inside the cores of neutron stars, but there had been no direct evidence of it before, Heinke said Sunday.
“We’ve seen superfluids in liquid helium on the Earth but this is the first time that we have direct evidence of it in the cores of neutron stars,” he said.
“We’re really understanding something that’s fundamentally important about what’s going on in the interiors of neutron stars, and neutron stars are some of the weirdest things in the universe and the things that are the most exotic in terms of how they behave, so it’s really fascinating.”
A neutron star is the ultradense core left behind after a supernova. A supernova happens when a massive star collapses at its core and releases a blast of energy that blows off its outer layers. Such a collapse can produce a black hole or its more visible cousin, a neutron star.
“Neutron stars are the densest matter that has not disappeared forever, beyond our universe, which is what black holes are,” Heinke explained.
Densely packed neutron stars are made up mainly of neutrons and cause matter to behave in strange ways that can’t be studied on Earth.
Heinke and his University of Southampton research partner Wynn Ho studied 10 years of data from NASA’s Chandra space satellite telescope and discovered last year that the neutron star inside Cassiopeia A was cooling. It is about 2 million C on the outside and had cooled by about four per cent over 10 years, Heinke said.
The pair consulted with Russian astrophysicists Peter Shternin and Dmitry Yakovlev who have expertise on temperatures in neutron stars and found the one at the centre of Cassiopeia A is cooling much faster than expected.
Heinke’s team of researchers as well as a separate team in Mexico, led by astrophysicist Dany Page, determined the rapid cooling must mean the neutron star contains a superfluid, an unusual state of matter that has “some really funky effects,” Heinke said.
Their results were published this month in the scientific journals Monthly Notices of the Royal Astronomical Society and Physical Review Letters, scientific journals.
“If something is a superfluid, that means it flows without any friction whatsoever,” explained Heinke. “So a normal river flowing along will have friction with the lake and it will cause turbulence and eddies and whatnot. A superfluid can flow without any friction.”
That state is only seen on Earth at very cold temperatures. Liquid helium can become a superfluid if it is cooled to a temperature slightly above absolute zero, or about -273 C, he said.
“If you have some water in a teacup, a little bit of water will kind of move up the edges of the teacup, just a little bit. It stops because it’s kind of running into some friction as it’s going (up) and that takes away its energy. The superfluid runs into no friction so it can actually flow up the side of the teacup and around (the edge) down and onto the base and then flow off your table and onto the floor. So the superfluid helium can’t be contained in a container if it’s got an open top. The top has to be closed, and very tightly.”
Neutron stars are so extremely dense that a superfluid would form inside such a star at a much higher temperature, somewhere in the hundreds of millions of degrees, Heinke said.
Along with the superfluid inside Cassiopeia A, the neutron star also contains a superconductor with a frictionless flow that keeps its charged particles moving, Heinke said.
“So it becomes a perfect electrical conductor, and that means that if you run a current through it, that current will never cease, it will never have any resistance,” he said.
“Similarly to superfluidity, superconductivity happens when you get below a certain temperature.”
Superconductors have been observed on Earth in extreme cold, around -100 C, he said. “So a really cold day in Antarctica is the highest temperature we’ve known for a superconductor, until now,” he said.
“This is actually the first time that we have evidence of a superconductor in the cores of neutron stars, and that’s really cool.”
A neutron star is so dense that a teaspoon of its matter would have a mass of about six billion tonnes, said Heinke, an assistant professor of physics who researches compact stars such as white dwarfs, neutron stars and black holes.
“Another way of putting it is that if you took all the humans, all seven billion of us or so on the planet, and squashed us down until we squished into the size of a sugar cube, that’s the density of a neutron star.”
Heinke said these findings help scientists understand how matter behaves at extremely high densities. “It has implications for nuclear physics for showing how these neutrons and protons interact at very high densities.”
and the closest neutron star is only 11000 light years away
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. I heard they were planning to use some kind of ceramic compound to get close to room-temperature superconducting...