Galaxies, unresolved star clusters, planetary nebulae
, and diffuse nebulae
of many types abound.
Despite their name, planetary nebulae
have nothing to do with planets.
What remains at their centers are white dwarf stars, which emit intense ultraviolet radiation that causes the gas in the nebulae
to glow and emit light in brilliant colors.
The stars associated with variable nebulae
are often situated just inside the edge of a dense molecular cloud through which one of the outflows has punched a conical cavity.
Located at a distance of between 1,500 and 5,000 light-years from Earth in the Aquarius constellation, this oddly-shaped nebula has been looked at once again by astronomers who are trying to understand why planetary nebulae
have unusual shapes.
Caption: Bright nebulae
and brilliant star clusters sparkle along the dark dust lanes of the Milky Way Galaxy.
Astronomers more than a century ago dubbed such gaseous structures planetary nebulae
because their disk like shape, as discerned in the telescopes of the day, reminded the researchers of planets.
Pictures presented in San Antonio on Tuesday to the American Astronomical Society reveal never-before-seen details of four "planetary nebulae
," enormous shells of hot gas thrown off during a star's death throes.
Of all the incredible parts of space, planets, black holes and asteroids to name a few, nebulae
remain one of the most breathtaking occurrences at the center of a number of images NASA releases.
Dark, or absorption, nebulae
are irregular stretches of dust and gas so dense that they block or scatter optical light, creating the appearance of dark voids in the eyepiece.
are glowing shells of gas around white dwarfs-Sun-like stars in the final stages of their lives.
To Herschel planetary nebulae
were small round objects which often appeared slightly greenish and which reminded him of Uranus, which he had discovered 6 years earlier.
Instead, they represent huge knots of gas that formed when spherical shells of material, known as planetary nebulae
, were ejected from the surface of a dying, sunlike star.
Imagers using modern CCD and DSLR cameras can try their hand at capturing these phantom nebulae
So why are these structures called "planetary" nebulae
if no planets are involved in their creation?