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TOPIC: Pulsars


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RE: Pulsars
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Title: Possible evidence that pulsars are quark stars
Authors: Renxin Xu (PKU)
(Version v2)

It is a pity that the real state of matter in pulsar-like stars is still not determined confidently because of the uncertainty about cold matter at supernuclear density, even 40 years after the discovery of pulsar. Nuclear matter (related to neutron stars) is one of the speculations for the inner constitution of pulsars even from the Landau's time more than 70 years ago, but quark matter (related to quark stars) is an alternative due to the fact of asymptotic freedom of interaction between quarks as the standard model of particle physics develops since 1960s. Therefore, one has to focus on astrophysical observations in order to answer what the nature of pulsars is. In this presentation, I would like to summarize possible observational evidence/hints that pulsar-like stars could be quark stars, and to address achievable clear evidence for quark stars in the future experiments.

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 Einstein's predicted distortion of space-time occurs around neutron stars, University of Michigan astronomers and others have observed. Using European and Japanese/NASA X-ray observatory satellites, teams of researchers have pioneered a groundbreaking technique for determining the properties of these ultradense objects.
Neutron stars contain the densest observable matter in the universe. They cram more than a sun's worth of material into a city-sized sphere, meaning a few cups of neutron-star stuff would outweigh Mount Everest. Astronomers use these collapsed stars as natural laboratories to study how tightly matter can be crammed under the most extreme pressures nature can offer.

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Astronomers using XMM-Newton and Suzaku have seen Einsteins predicted distortion of space-time and pioneered a ground-breaking technique for determining the properties of neutron stars.
 ESAs XMM-Newton and the JAXA/NASA Suzaku X-ray observatories have been used to see the distortion of space-time around three neutron stars. These objects contain the densest observable matter in the Universe.

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It was one of the most important astronomical discoveries of the twentieth century, and it became one of the more controversial when only one of the discoverers received a Nobel prize. Now a fascinating new footnote has been added to the story of how pulsars were discovered with the revelation that some had previously been observed by a US Air Force staff sergeant at a remote Alaskan outpost.
Earlier this month, 81-year-old Charles Schisler came forward to tell the story of how he used a military radar to identify around a dozen radio sources, some of which were pulsars. Astronomers who have seen Schisler's meticulous logs believe that he spotted a bright pulsar in the nearby Crab Nebula months before the first scientific observation of a pulsar was published in Nature.

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Title: Pulsar slow glitches in a solid quark star model
Authors: C. Peng (PKU), R. X. Xu (PKU)

A series of five unusual slow glitches of the radio pulsar B1822-09 (PSR J1825-0935) were observed over the 1995-2005 interval. This phenomenon is understood in a solid quark star model, where the reasonable parameters for slow glitches are presented in the paper. It is proposed that, because of increasing shear stress as a pulsar spins down, a slow glitch may occur, beginning with a collapse of a superficial layer of the quark star. This layer of material turns equivalently to viscous fluid at first, the viscosity of which helps deplete the energy released from both the accumulated elastic energy and the gravitation potential. This performs then a process of slow glitch. Numerical calculations show that the observed slow glitches could be reproduced if the effective coefficient of viscosity is ~10² cm²/s and the initial velocity of the superficial layer is order of 10^{-10} cm/s in the coordinate rotating frame of the star.

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Title: Modelling Dense Stellar Systems
Authors: Piet Hut, Shin Mineshige, Douglas C. Heggie, Junichiro Makino

Black holes and neutron stars present extreme forms of matter that cannot be created as such in a laboratory on Earth. Instead, we have to observe and analyse the experiments that are ongoing in the Universe. The most telling observations of black holes and neutron stars come from dense stellar systems, where stars are crowded close enough to each other to undergo frequent interactions. It is the interplay between black holes, neutron stars and other objects in a dense environment that allows us to use observations to draw firm conclusions about the properties of these extreme forms of matter, through comparisons with simulations. The art of modelling dense stellar systems through computer simulations forms the main topic of this review.

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The video is an artist's concept of accretion spinning a pulsar to the millisecond range, a nuclear explosion on the surface of a pulsar, emitted gravitational waves, and a supernova.

[youtube=http://youtube.com/watch?v=pk-wJzHZ6GU]

The audio is the sound of five different pulsars. Below is a list of the pulsars in the order they are presented.

PSR B0329+54
PSR B0833-45 (Vela Pulsar)
PSR B0531+21 (Crab Pulsar)
PSR J0437-4715
PSR B1937+21


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Jets from neutron star
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Jets from neutron star rival those made by black holes
One of the astonishing qualities of a black hole is its ability to power great jets of energy and matter into space.
Now, using NASA's orbiting Chandra X-ray Observatory, a team of astronomers led by Sebastian Heinz of the University of Wisconsin-Madison has obtained evidence that neutron stars the dense, collapsed cores of exploded stars produce jets that, relatively speaking, rival those produced by black holes.
The new work is important because it reveals the first known neutron star with a powerful large-scale jet, a quality previously attributed only to black holes. Because jets can be diagnostic of extreme objects like black holes and their environments, the new finding may help astrophysicists better understand the nature of both black holes and neutron stars.

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Neutron star cores
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Title: Quark deconfinement in neutron star cores and the ground state of neutral matter
Authors: Chang-Qun Ma, Chun-Yuan Gao

Whether or not deconfined quark phase exists in neutron star cores and represents the ground state of neutral matter at moderate densities are open questions. We use two realistic effective quark models, the three-flavour Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to describe the neutron star matter. After constructing possible hybrid equations of state (EOSes) with unpaired or color superconducting quark phase, we systematically discuss the observational constraints of neutron stars on the EOSes. It is found that the neutron star with pure quark matter core is unstable and the hadronic phase with hyperons is denied, while hybrid EOSes with two-flavour colour superconducting phase or unpaired quark matter phase are both allowed by the tight and most reliable constraints from two stars Ter 5 I and EXO 0748-676. And the hybrid EOS with unpaired quark matter phase is allowed even compared with the tightest constraint from the most massive pulsar star PSR J0751+1807. Therefore, we conclude that the ground state of neutral matter at moderate densities is in deconfined quark phase likely.

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Neutron stars
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Title: The physics of strong magnetic fields in neutron stars
Authors: Qiu-he Peng, Hao Tong

In this paper we present a new result, namely that the primal magnetic field of the collapsed core during a supernova explosion will, as a result of the conservation of magnetic flux, receive a massive boost to more than 90 times its original value by the Pauli paramagnetisation of the highly degenerate relativistic electron gas just after the formation of the neutron star. Thus, the observed super-strong magnetic field of neutron stars may originate from the induced Pauli paramagnetisation of the highly degenerate relativistic electron gas in the interior of the neutron star. We therefore have an apparently natural explanation for the surface magnetic field of a neutron star.

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