Clingy dark matter may slow the spin of corpse stars - physics-math - 23 June 2014 - New Scientist

Clingy dark matter may slow the spin of corpse stars - physics-math - 23 June 2014 - New Scientist: Their strong magnetic fields gradually slow their spin, but over the past 15 years, astronomers have noticed that many pulsars are slowing more than we would expect.

Chris Kouvaris at the University of Southern Denmark thinks a form of dark matter with a tiny electric charge may be putting on the brakes.

Black Holes Feed On Quantum Foam, Says Cosmologist — The Physics arXiv Blog — Medium

Black Holes Feed On Quantum Foam, Says Cosmologist — The Physics arXiv Blog — Medium: “Quantum fluctuations in the form of mini black holes can couple to macroscopic black holes and allow the latter to grow exponentially...”

He says this kind of growth can easily account for the observed size of relatively young supermassive black holes. And he goes on to predict that this mechanism could allow smaller black holes to grow too. In fact, he suggests these smaller objects, which would be difficult to observe from Earth, could make up a significant fraction of the mysterious dark matter that astronomers believe the universe must contain.

...He says that this quantum feeding mechanism must apply to the supermassive black hole at the centre of our galaxy and that consequently, it must be growing at the rate of about 10^-3 solar masses per year.

Twist in dark matter tale hints at shadow Milky Way

Twist in dark matter tale hints at shadow Milky Way: In 2008, when the PAMELA satellite found a similar excess of positrons, Neal Weiner of New York University and colleagues suggested that WIMPs are drawn together under a force of their own...

Observations of the orbits of stars around galaxies suggest that all galaxies, including the Milky Way, are surrounded by a spherical cloud of dark matter (see diagram). But if a fraction of dark matter particles interact with each other, they would combine into atom-like structures and eventually collapse into a spinning disc. This is how ordinary matter formed the Milky Way. The resulting shadow Milky Way could be spinning right along with the visible one, or it could end up tilted at a slight angle, she adds.

Astrophile: The case of the disappearing pulsar - New Scientist - New Scientist

Astrophile: The case of the disappearing pulsar: The star was a spectacular find: unlike every other pulsar ever observed, this one was in a close binary orbit with another pulsar. Together, the pair provided a precise laboratory to test Einstein's theory of general relativity, and a means of detailing how pulsars behave.
But in March 2008, Pulsar B went dark...
No one snuffed out Pulsar B – it just rotated out of view...

"We can see the light from one pulsar being bent as it travels through the gravitational well of the other pulsar," she says. "It's really neat. We have proof that one of these objects is distorting spacetime."
The eclipsing pulsars also provided a test of "spin precession", the idea that the pulsars' axes should wobble around like a top as they spin.

Short Sharp Science: Spinning space telescope's view of a pulsar

Short Sharp Science: Spinning space telescope's view of a pulsar: It can't be so easy to keep the Fermi Gamma-ray Space Telescope trained on one spot in the sky as it maps the universe. Fermi orbits the Earth every 95 minutes while rocking between the north and the south on alternate orbits, On top of this, the satellite also completes one rotation every 54 days to keep its solar panels facing the sun.

This image traces Fermi's view via its Large Area Telescope of the gamma rays emitted by the Vela pulsar from August 2008 to August 2010. The Vela pulsar is a neutron star, itself spinning at a dizzying 11 times per second and the brightest and most persistent source of gamma rays in the sky, giving an anchoring point for Fermi's own spin.

Astrophile: Stopped clocks deepen pulsar enigmas

Astrophile: Stopped clocks deepen pulsar enigmas:  In the 1970s, some regular pulsars were spotted switching off for a few seconds to a few minutes, a phenomenon known as "nulling". And in the past decade, a new class of pulsars has been found , in which the silences can range from minutes to a few hours. They were dubbed rotating radio transients, or RRATs. Around the same time, a pulsar was found that pulsed for about a week and then switched off for about a month before repeating the cycle.

With an "off" period of 580 days, Camilo's pulsar has taken by far the longest break seen so far. Having switched back on only in August this year, it is too early to tell whether the year on/year-and-a-half off cycle is a regular thing, but Camilo says it makes him wonder what other pulsars are hiding.

Blog - Pulsars Are Giant Permanent Magnets, Say Physicists

Blog - Pulsars Are Giant Permanent Magnets, Say Physicists: Another problem is how pulsars end up with magnetic fields that are so strong. The conventional view is that the process of collapse during a supernova somehow concentrates the original star's field. However, a star loses much of its material when it explodes as a supernova and this presumably carries away much of its magnetic field too. But some pulsars have fields as high as 10^12 Tesla, far more than can be explained by this process.

Today, Johan Hansson and Anna Ponga at Lulea University of Technology in Sweden suggest a clever way out of this conundrum. They point out that there is another way for magnetic fields to form, other than the movement of charged particles. This other process is by the alignment of the magnetic fields of the body's components, which is how ferromagnets form.

Their suggestion is that when a neutron star forms, the neutron magnetic moments become aligned because this is the lowest energy configuration of the nuclear forces between them. When this alignment takes place, a powerful magnetic field effectively becomes frozen in place.

Black holes and pulsars could reveal extra dimensions - space - 21 August 2011 - New Scientist

Black holes and pulsars could reveal extra dimensions: Black holes are predicted to fritter away their mass over time by emitting particles, a phenomenon called Hawking radiation. Without extra dimensions, this process is predicted to be agonisingly slow for run-of-the-mill black holes weighing a few times as much as the sun, making it impossible to measure.

Extra dimensions would give the particles more ways to escape, speeding up the process.

Physicists hit on mathematical description of superfluid dynamics

Physicists hit on mathematical description of superfluid dynamics: As a neutron star rotates, the superfluid on the surface behaves quite differently than a liquid would on the surface of the Earth. As the rotational speed increases the fluid opens a series of small vortices. As the vortices assemble into triangular patterns, the triangles build a lattice structure within the superfluid.
"When you reach the correct speed, you'll create one vortex in the middle," Bulgac said. "And as you increase the speed, you will increase the number of vortices. But it always occurs in steps."

Superconductivity's Smorgasbord of Insights: A Movable Feast

Superconductivity's Smorgasbord of Insights: A Movable Feast: Physicists have applied the theory of superconductivity directly to nuclear matter, liquid helium, and ultracold atomic gases. Historically, insights from superconductivity convinced theorists of the importance of symmetries and the ways in which a physical system can muddle or “break” them. The concept of “spontaneous symmetry breaking” now undergirds theory in many fields, especially particle physics. “It was not a way that people were thinking, certainly not in elementary particle physics,” says Gordon Baym, a theorist at the University of Illinois, Urbana-Champaign. Superconductivity, he says, “changed the way people thought in different fields..."


The BCS model was more than a one-trick pony. Bardeen, Cooper, and Schrieffer had based it on just two assumptions: that the particles are fermions and that they attract each other. So “it was obvious to all of us” that the theory would apply to other particles interacting through different forces, Cooper says.
First came applications to atomic nuclei. In the summer of 1957, before the BCS theory was published, Pines visited the University of Copenhagen. There he, Aage Bohr (Niels Bohr's son), and Ben Mottelson found they could explain long-standing puzzles, such as why nuclei with an even number of protons and even number of neutrons are particularly tightly bound. The protons and neutrons, also fermions, independently pair.

Neutron Star Provides Direct Evidence for Bizarre Type of Nuclear Matter - ScienceNOW

Neutron Star Provides Direct Evidence for Bizarre Type of Nuclear Matter - ScienceNOW: Scientists have accumulated indirect evidence for such pairing and superfluidity. For example, spinning neutron stars called pulsars emit clocklike streams of electromagnetic pulses. Usually incredibly steady, that pulsing sometimes speeds up abruptly. Such "pulsar glitches" likely result from brief interactions between the neutron star's solid crust and superfluid interior...
...Chandra data showed Cas A was cooling so fast that they could measure the change. So instead of looking at many neutron stars, researchers needed to look at only this one. "This is definitely the first time that we've been able to see an appreciable temperature change in a neutron star..."

Galactic GPS Put Through Its Paces - Technology Review

Galactic GPS Put Through Its Paces - Technology Review: "Soon after pulsars were discovered, astronomers and science fiction writers began to speculate about the possibility of using pulsars as celestial navigation beacons allowing interstellar travellers to find their way home, rather like the GPS system we have now.

That's a simple idea but it belies some technical difficulty. At the speeds that most astronomical objects are travelling, relativity becomes important and that significantly increases the complexity of the calculations."

Cosmic clocks: Relativity's final test

This is about pulsars

http://www.newscientist.com/article/mg20527520.200-cosmic-clocks-relativitys-final-test.html