The "Helix Nebula" is a planetary nebula in the constellation Aquarius. It is 700 light years (400 trillion miles) from Earth, and is a mere 2.5 light years wide subtending an angular size of 25 arcminutes (roughly the same size as a full Moon). Due to its very low intrinsic brightness it cannot be seen with the naked eye, and is a faint, grayish circle in small, amateur telescopes.
According to current theory, a planetary nebula occurs toward the end of the burning cycle of a star with a "main sequence mass" of up to 5 times the Sun's mass. The relentless inward force of gravity overcomes the diminishing outward force exerted by nuclear fusion reactions as the star's hydrogen and helium "fuel" is converted to energy and heavier elements, and the star suddenly "implodes" inward. This process is very fast, and is stopped abruptly in its tracks by "electron degeneracy" (electron orbits are literally in contact with each other, which produces a strong repulsive force that halts further stellar contraction). The result is a small, hot white dwarf star which can be seen in the center of the nebula. Such stars are very dense, A star the size of our Sun would be shrunk a million-fold to the size of Earth, with a resulting density of 15 tons per tablespoon. "Stellar wind” and intense UV radiation blow away the surrounding envelope of unfused gases, and illuminate it. A planetary nebula results (always with a central white dwarf star). Since some of these objects “look like” planets in small telescopes, they were given the name planetary nebula many years ago. Note that the expanding envelope is only visible for a few tens of thousands of years. It eventually becomes too diffuse to detect. So, all the planetary nebulae we see are relatively recent phenomena.
One more point. Stars with an initial mass of about 10 solar masses or more end their lives in a very different way (becoming either a neutron star, supernovae, or black hole). But, stars of 10 solar masses are very rare. The vast majority of stars are red dwarfs.
The Helix Nebular (NGC 7293)
Date Taken:July 29, 2014
Location Taken:Siding Spring Observatory, NSW Australia
Conditions of Location: Equipment Used:Planewave 27" corrected Dall-Kirkham telescope, FLI PL09000 camera
Processing Used:10x5 minutes luminance, 8 x 3 minutes RGB for a total exposure of 2 hours, processed in Maxim DL and Photoshop
Distance from Location:700 light years
Constellation:Aquarius
Other Link:
Amazing photo! Luke and I are impressed. Our family attended the Creation Museum in KY recently, and saw an IMAX movie called the Created Cosmos, about the infinity of space — incredible. Your pic reminded me of it. Thanks for your work!