Cassiopeia's heart1)Not to be confused by the heart nebula, a massive star-forming region on the cassiopeia border , the nameless middle star of the conspicuous 'W' in the sky, shows a surprise in this deep image.
The big questions of astronomy these days are: what is the nature of dark matter and dark energy? How short after the big bang did the forces of nature decouple? And how will it all end?
But besides these big riddles, there are many more unsolved smaller mysteries much closer to home. 550 light years close, to be precise. The first little mystery is relatively benign. The brightest stars of Cassiopeia are Schedar, Caph, γ-Cas, Ruchbah, Segin, and Achird. Why doesn't the third (γ) star have its own name? Even more striking considering that it is the middle star of the 'W', and quite prominent at magnitude +2.47. This serious omission was amended only in recent times, when during the Apollo era it was christened Navi, to emphasize its prominent role in space navigation, apparantly because γ Cas is instantly recognized from outer space.
Of much more serious concern is the fact that γ Cas, optically the brightest member of a special class called Be stars, has an unseen low mass (~1.0M) companion of unknown nature, orbiting γ Cas in 204 days in a tight, nearly circular orbit. Be-stars are 2)A thorough introduction into the nature of Be-stars is given here here a class of very hot, very large stars of spectral type B that spin so fast that they almost break up. In the process of almost breaking up, they flatten out along the equator to form a thin, gaseous disk. This disk is formed by matter breaking free from the stellar surface due to the high centrifugal force. In contrast to the more commonly known accretion disks (formed around black holes), these disks are called decretion disks, and these disks add their own features to the star's spectrum in the form of pronounced Ballmer-lines with narrow emission profile.
γ Cas is also an X-ray source, as much as 10% of the sun's total emission in the entire spectrum is being poured out by γ Cas as hard X-rays. Since this is not normal behavior for a Be-star, it has been theorized for a long time that γ Cas' unseen companion must have something to do with it, probably being a white dwarf (WD) or even neutron star (NS) scooping up matter from its host star and releasing it as pure X-rays when the matter comes crashing down with near light-speed as it hits the surface of the degenerate companion. The only problem with this model, is that the spectral properties of the X-rays do not match at all with that of known typical compact binary systems. A recent paper 3)A propelling neutron star in the enigmatic Be-star γ~Cassiopeia link, however, argues that under certain conditions it is very hard for accreted star-stuff from γ Cas to actually reach the NS' surface, rather, it collides with the NS magnetosphere producing a different kind of X-rays that match observations really well. If confirmed for other systems, this would lend credible evidence to the theory that the unseen companion is indeed a NS after all.
IC 63 & IC 59
γ Cas is itself embedded in a rather large 2° bubble of relatively dense interstellar matter. With spectral type B0, γ Cas emits most of its energy in the UV range, but being an additional strong X-ray source, it is bound to have an ionizing effect on the larger area. As a result, within this ISM, only two high density clumps are left over, called IC 63 and IC 59 4)See: A multiwavelength study of IC 63 and IC 59 link, the rest no doubt long gone. The direction of cometary nebula IC 63 is clearly coincident with the line of sight of γ Cas. Where γ Cas shines directly on the matter, it is ionized, forming an ionization front (visible as a thin red edge around the brighter, blue part of the nebula). Because the ionization front appears very thin, it is reasonable to assume that we are looking at it edge-on. This would imply a nearly identical distance to IC 63 and γ Cas.
References [ + ]
|1.||↑||Not to be confused by the heart nebula, a massive star-forming region on the cassiopeia border|
|2.||↑||A thorough introduction into the nature of Be-stars is given here here|
|3.||↑||A propelling neutron star in the enigmatic Be-star γ~Cassiopeia link|
|4.||↑||See: A multiwavelength study of IC 63 and IC 59 link|