An astronomical ghost looks down on all the little witches and goblins prowling the streets tonight: a "dead" star known as the Ghost of Jupiter. It's a type of object called a planetary nebula, which forms when a star like the Sun dies. The star expels its outer layers of gas into space, where they are illuminated by radiation from the star's hot, dense core. This is an ultraviolet view of the nebula (bright blue area at center) and tendrils of gas around it. The nebula isn't related to Jupiter in any way. To early telescopic observers, its image through the eyepiece simply resembled Jupiter. [NASA/JPL]
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Astronomical ghosts creep across the sky on this Halloween night. There's nothing supernatural about them, though -- they simply have a ghostly appearance.
One of them is the Ghost of Mirach. It's a fairly small galaxy that's about 10 million light-years away. It looks "ghostly" because it's immersed in the glare of the bright star Mirach, which is high in the east at nightfall.
To learn much about the galaxy, astronomers have to study it in wavelengths that are invisible to the human eye -- particularly the ultraviolet. Those wavelengths reveal a ring of bright, hot young stars around the galaxy's core. The ring may have formed a billion years ago when the Ghost interacted with another galaxy. The interaction squeezed giant clouds of gas and dust, triggering the birth of many new stars.
The other ghost climbs into the sky in the wee hours of the morning, far to the lower right of the Moon -- the Ghost of Jupiter. It's not related to Jupiter at all -- it just looked big and round to early telescopic observers -- like Jupiter.
While the "Jupiter" part of the name doesn't really fit, the "Ghost" part may. The object is an expanding shell of gas and dust that was expelled by a dying star. In essence, it's carrying away much of the life of the star, so as it fades away, only the star's small core will be left behind -- and the star will be but a ghost of its once-mighty self.
Script by Damond Benningfield, Copyright 2010
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