* Astronomy

Blobrana · L

RE: PSR J1719-1438

Blobrana · L

Title: Evolutionary trajectories of ultra-compact "black widow" pulsars with very low mass companions
Authors: O. G. Benvenuto, M. A. De Vito, J. E. Horvath

The existence of millisecond pulsars with planet-mass companions (Bailes et al., 2011) in close orbits is challenging from the stellar evolution point of view. We calculate in detail the evolution of binary systems self-consistently, including mass transfer, evaporation and irradiation of the donor by X-rays feedback, demonstrating the existence of a new evolutionary path leading to short periods and compact donors as required by the observations of PSR J1719-1438. We also point out the alternative of an exotic nature of the companion planet-mass star.

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Blobrana · L

Title: Formation of the planet around the millisecond pulsar J1719-1438
Authors: L. M. van Haaften, G. Nelemans, R. Voss, P. G. Jonker

Context. Recently the discovery of PSR J1719-1438, a 5.8 ms pulsar with a companion in a 2.2 hr orbit, was reported. The combination of this orbital period and the very low mass function is unique. The discoverers, Bailes et al., proposed an ultracompact X-ray binary (UCXB) as the progenitor system. However, the standard UCXB scenario would not produce this system as the time required to reach this orbital period exceeds the current estimate of the age of the Universe. The detached state of the system aggravates the problem.
Aims. We want to understand the evolutionary history of PSR J1719-1438, and determine under which circumstances it could have evolved from an UCXB.
Methods. We model UCXB evolution varying the donor size and investigate the effect of a wind mass loss from the donor, and compare the results with the observed characteristics of PSR J1719-1438.
Results. An UCXB can reach a 2.2 hr orbit within the age of the Universe, provided that 1) the millisecond pulsar can significantly heat and expand the donor by pulsar irradiation, or 2) the system loses extra orbital angular momentum, e.g. via a fast wind from the donor.
Conclusions. The most likely scenario for the formation of PSR J1719-1438 is UCXB evolution driven by angular momentum loss via the usual gravitational wave emission, which is enhanced by angular momentum loss via a donor wind of ~3x10^-13 solar masses/yr. Depending on the size of the donor during the evolution, the companion presently probably has a mass of ~1-3 Jupiter masses, making it a very low mass white dwarf as proposed by Bailes et al. Its composition can be either helium or carbon-oxygen. A helium white dwarf companion makes the long (for an UCXB) orbital period easier to explain, but the required inclination makes it a priori less likely than a carbon-oxygen white dwarf.

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Blobrana · L

Title: Transformation of a Star into a Planet in a Millisecond Pulsar Binary
Authors: M. Bailes, S. D. Bates, V. Bhalerao, N. D. R. Bhat, M. Burgay, S. Burke-Spolaor, N. D'Amico, S. Johnsto, M. J. Keith, M. Kramer, S. R. Kulkarni, L. Levin, A. G. Lyne, S. Milia, A. Possenti, L. Spitler, B. Stappers, W. van Straten

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7 ms pulsar, was detected in a recent survey with the Parkes 64m radio telescope. We show that it is in a binary system with an orbital period of 2.2 h. Its companion's mass is near that of Jupiter, but its minimum density of 23 g cm^{-3} suggests that it may be an ultra-low mass carbon white dwarf. This system may thus have once been an Ultra Compact Low-Mass X-ray Binary, where the companion narrowly avoided complete destruction.

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Blobrana · L

A Planet made of Diamond

A star that was transformed and condensed into a planet made of solid diamond,: that's what astronomers think they've found recently. The discovery was made by an international research team with scientists from Australia, Germany, Italy, the UK and the USA, including Prof. Michael Kramer from Max Planck Institute for Radio Astronomy in Bonn, Germany. The team was able to detect the "diamond planet" with the 64-m radio telescope in Parkes, Australia, and found out that it orbits an unusual star known as a pulsar. The astronomers consolidated their findings with follow-up observations with the Lovell radio telescope in the UK and one of the Keck telescopes on Hawaii. The pulsar and its planet lie 4,000 light years away in the constellation of Serpens. The system is about an eighth of the way towards the Galactic Centre from the Earth and is part of the Milky Way's plane of stars. This exiting result is reported in the recent issue of "Science Express".
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PulsarPlanet_HD_MOV.mov
PulsarPlanet_Large_H264.mp4
PulsarPlanet_Medium_H264.mp4
PulsarPlanet_Mobile_H264.mp4
PulsarPlanet_Poster_PSD.PSD

Blobrana · L

The Diamond Planet

A once-massive star that's been transformed into a small planet made of diamond: that is what University of Manchester astronomers think they've found in the Milky Way.
The discovery has been made by an international research team, led by Professor Matthew Bailes of Swinburne University of Technology in Melbourne, Australia, and is reported in the journal Science.
The researchers, from The University of Manchester as well as institutions in Australia, Germany, Italy, and the USA, first detected an unusual star called a pulsar using the Parkes radio telescope of the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) and followed up their discovery with the Lovell radio telescope, based at Jodrell Bank Observatory in Cheshire, and one of the Keck telescopes in Hawaii.
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