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TOPIC: Cassiopeia A
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Title: A neutron star with a carbon atmosphere in the Cassiopeia A supernova remnant
Authors: Wynn C. G. Ho & Craig O. Heinke

The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) are expected. Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars. Here we report an analysis of archival observations of the compact X-ray source in the centre of the Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star (with low magnetic field) produces a good fit to the spectrum. Our emission model, in contrast with others, implies an emission size consistent with theoretical predictions for the radius of neutron stars. This result suggests that there is nuclear burning in the surface layers and also identifies the compact source as a very young (approx330-year-old) neutron star.

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3D FlyThrough of Cassiopeia A
Cassiopeia A in 60 Seconds
Cassiopeia A 3d 02


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This Chandra X-ray Observatory image shows the central region of the supernova remnant Cassiopeia A (Cas A, for short) the remains of a massive star that exploded in our galaxy. Evidence for a thin carbon atmosphere on a neutron star at the center of Cas A has been found. Besides resolving a ten-year-old mystery about the nature of this object, this result provides a vivid demonstration of the extreme nature of neutron stars. An artist's impression of the carbon-cloaked neutron star is also shown.

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Discovered in Chandra's "First Light" image obtained in 1999, the point-like X-ray source at the center of Cas A was presumed to be a neutron star , the typical remnant of an exploded star, but it surprisingly did not show any evidence for X-ray or radio pulsations. By applying a model of a neutron star with a carbon atmosphere to this object, it was found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because this neutron star would be unlikely to display any changes in its intensity as it rotates. The result also provides evidence against the possibility that the collapsed star contains strange quark matter.

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Position (2000):      RA 23h 23m 26.7s | Dec +58° 49' 03.00"

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A physicist from the University of Alberta is part of a team that has identified an unusual neutron star left over from a supernova first seen 330 years ago.
Craig Heinke and his colleague Wynn Ho at the University of Southampton, U.K., say that the remnant of the supernova Cassiopeia A is a very young neutron star, 20 times heavier than the sun, but only 20 kilometres wide.
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Title: A dedicated Chandra ACIS observation of the central compact object in the Cassiopeia A supernova remnant
Authors: G.G. Pavlov, G.J.M. Luna
(Version v2)

We present results of a recent Chandra X-ray Observatory observation of the central compact object (CCO) in the supernova remnant Cassiopeia A. This observation was obtained in an instrumental configuration that combines a high spatial resolution with a minimum spectral distortion, and it allowed us to search for pulsations with periods longer than 0.68 s. We found no evidence of extended emission associated with the CCO, nor statistically significant pulsations (the 3-sigma upper limit on pulsed fraction is about 16%). The fits of the CCO spectrum with the power-law model yield a large photon index, Gamma\approx 5, and a hydrogen column density larger than that obtained from the SNR spectra. The fits with the blackbody model are statistically unacceptable. Better fits are provided by hydrogen or helium neutron star atmosphere models, with the best-fit effective temperature kT_{eff}^\infty \approx 0.2 keV, but they require a small star's radius, R = 4 - 5.5 km, and a low mass, M < 0.8 M_sol. A neutron star cannot have so small radius and mass, but the observed emission might emerge from an atmosphere of a strange quark star. More likely, the CCO could be a neutron star with a nonuniform surface temperature and a low surface magnetic field (the so-called anti-magnetar), similar to three other CCOs for which upper limits on period derivative have been established. The bolometric luminosity, L_{bol}^\infty ~ 6 x 10^{33} erg s^{-1}, estimated from the fits with the hydrogen atmosphere models, is consistent with the standard neutron star cooling for the CCO age of 330 yr. The origin of the surface temperature nonuniformity remains to be understood; it might be caused by anisotropic heat conduction in the neutron star crust with very strong toroidal magnetic fields.

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Interstellar space dust from a dead star identified by a research team led by The University of Nottingham could unlock some of the mysteries of the early universe.
Dr Loretta Dunne and her team have found new evidence of huge dust production in the Cassiopeia A supernova remnant, the remains of a star that exploded about 300 years ago. The paper is set to be published in the Monthly Notices of the Royal Astronomical Society.
Interstellar dust is found throughout the cosmos. It is responsible for the dark patches seen in the Milky Way on a moonless night. It consists of carbon and silicate particles, about the size of those in cigarette smoke. The dust helps stars like the Sun to form and subsequently coagulates to form planets like Earth and the cores of giant gas planets like Jupiter. It is found in huge quantities in galaxies, even very early in the history of the universe.
But the origin of all this dust is a mystery. Does it condense like snowflakes in the winds of red giant stars or is it produced in supernovae - the violent death-throes of massive stars? Supernovae are an efficient way of producing dust in a blink of the cosmic eye, as massive stars evolve relatively quickly, taking a few million years to reach their supernova stage. In contrast lower-mass stars like our Sun take billions of years to reach their dust-forming red giant phase. Despite many decades of research, astronomers have still not found conclusive evidence that supernovae can produce dust in the quantities required to account for the dust they see in the early universe.

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Cassiopeia A Supernova Remnant
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Title: Carbon Monoxide in the Cassiopeia A Supernova Remnant
Authors: J. Rho, T. H. Jarrett, W. T. Reach (IPAC/Caltech), H. Gomez (Cardiff U.), M. Andersen (SSC/IPAC)

We report the likely detection of near-infrared 2.29 \mu m first overtone Carbon Monoxide (CO) emission from the young supernova remnant Cassiopeia A (Cas A). The continuum-subtracted CO filter map reveals CO knots within the ejecta-rich reverse shock. We compare the first overtone CO emission with that found in the well-studied supernova, SN 1987A and find ~30 times less CO in Cas A. The presence of CO suggests that molecule mixing is small in the SN ejecta and that astrochemical processes and molecule formation may continue at least ~300 years after the initial explosion.

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A team of astronomers including a University scientist has created the first three-dimensional reconstruction of the remnants of an exploding star.
Dr Haley Gomez, of the School of Physics and Astronomy is part of an international group that has produced a 3-D model of the supernova remnant Cassiopeia A, the remains of a star thought to have exploded 330 years ago.
Using X-Ray images, and infrared data, the team led by Dr Tracey DeLaney of the Massachusetts Institute of Technology, created the visualisation of the supernova to get a more complete understanding of how the explosion happened.
The model brought together the best techniques from the fields of astronomy and medical imaging, and allowed the group to identify a number of new findings. One of the notable features revealed by the 3-D visualisation were high velocity plumes and jets shooting out from the explosion. Astronomers had known about the plumes and jets before, but did not know that they all came out in a broad, disk-like structure.  Any future models of stellar explosions must now consider this new observational finding.

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University of Minnesota astronomers led an international team of researchers who have developed a new three-dimensional visualization of the famous Cassiopeia A supernova remnant that gives astrophysicists new clues about how exploding stars form new stars and solar systems. The findings were presented nationally for the first time this week during the American Astronomical Society meeting in Long Beach, Calif.

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3D Fly-Through of the Supernova Remnant, Cassiopeia A



Time Lapse Movie of the Cassiopeia A Supernova Remnant



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