Exploded Star visible this month

Published 3:16 pm Friday, August 13, 2010

After sunset on warm August nights, once the sky has become completely dark, a properly aimed telescope will reveal a faintly glowing ring of smoke directly overhead that is all that seems to remain of a once majestic star.

The star had burned steadily for perhaps eight billion years as a sun much like our own, perhaps a little larger and a little brighter, but otherwise almost exactly the same. During its lifetime the star had managed to perform an intricate balancing act whereby the contracting force of its own gravity was exactly offset by the expanding force of nuclear reactions at its center. From a distance the star would have seemed constant, quiet and unchanged.

There came a time, however, when the stars nuclear fuel began to run low and gravity gained the upper hand. As it did, the star began to contract, slowly at first and then more rapidly.

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As the star contracted, it became hotter, and with the increased heat came increased radiation pressure at its surface. Thus, in a manner of speaking, the outward pressure which had previously been at the stars center was replaced with outward pressure at its surface causing the surface layers of the star to expand.

This reversal of pressure in stars nearing the end of their lives causes a situation in which the core of the star contracts while the perimeter expands. As the visible outer portion of the star moves away, it becomes cooler, the overall size of the star becomes larger and the light emitted from the stars surface moves to the long wavelength red end of spectrum. The result is a star known as a red giant.

Eventually, the expanding outer layers of the star separate completely so that the compressed center of the star is revealed. This remnant core of the star has become so hot that its light shifts to the short wavelength blue-white end of the spectrum. The star in this final evolutionary stage of its life is known as a white dwarf.

The exploded star that is the subject of this article is a white dwarf star whose outer layers have exploded into space as described above. But what makes this particular object so interesting and beautiful is that its outer atmosphere, though separated from the star, has not yet separated far enough to become invisible. Rather, as if from a recently extinguished fire, it has coalesced into a smoke ring of light encircling the central white dwarf star, and the object is therefore known as the Ring Nebula.

Join the astronomers at FENCE on Saturday after sunset, August 14th where telescopes will be set up on the hilltop behind the main building to observe not only the Ring Nebula, but also the many other equally magnificent celestial wonders that abound in the Summer Milky Way.

Any and all questions will be answered (Questions about astronomy, that is!).

And dont forget to bring your binoculars!