Tuesday, 17 April 2018

EGB6: Interesting faintness

Yes, I simply love the challenge of spotting extremely faint objects and especially large, frail planetary nebula in the last stage of their existence. As you know, when a star dies, it suddenly expels its outer layers which are subsequently blown away by the violent radiation of the remaining stellar core, the so-called "white dwarf". After many millennia, however, these shells of hot gas grow so large and thin that they start to dissolve in the void of space. This is exactly what we witness here, in this extremely large planetary that was discovered in 1984 by Ellis, Grayson and Bond. Visually this is one of the toughest objects to see and it was not without difficulty that I managed to discern its broken annular shape, with its western rim slightly brighter. Nevertheless it was just a tad easier than PuWe1, which was really on the limit of visibility.

How difficult they may be for us, humble visual amateurs, these extremely old and diffuse planetaries offer a great opportunity for scientific study, more specifically in the way they dissolve into space and how their central star extinguishes. In the case of EGB6, another very interesting discovery was made. Strange infrared emission knots in the spectrum of its central star, pointed to the existence of an obscure companion star, probably a faint red dwarf. Recent observations with the Hubble space telescope, revealed that some of the expelled matter of the central star was captured into an accretion disk around this companion!

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