Hubble's Gallery of Planetary Nebulae
Until now, the demise of a Sun-like star was thought to be a fairly simple process: the star gracefully sheds a shell of glowing gas and then settles into a long retirement as a burned-out white dwarf. But now, several teams of astronomers have released a beautiful collection detailed images obtained with the help of NASA's Hubble Space Telescope. The views reveal surprisingly intricate patterns spun into space by aging stars: pinwheels, sprinkler-like jets, graceful goblet shapes, and even some that look like a rocket engine jet. "These terrifying fireworks display a preview of the final stages of our own Sun," says Bruce Balick of the University of Washington in Seattle. The bursts are more than just a stellar "light show." At the star's core, heavier elements - mostly carbon - are produced and then hurled into interstellar space as raw material for subsequent generations of stars, planets, and possibly life.
According to astronomers, the incandescent sculptures are forcing a rethinking of previous theories of stellar evolution. In particular, the patterns could arise from the interplay of an aging star with unnoticed companions - such as planets, brown dwarfs or smaller companion stars.
M2-9 is a notable example of a "butterfly" or bipolar planetary nebula. Another more revealing name is Twin Jet Nebula. In a cross-section of the nebula, each side appears like a pair of jets from a jet engine. In fact, based on the shape of the nebula and the measured speed of the gas of 320 kilometers per second, astronomers believe that the supersonic jet description is quite accurate. Studies conducted from the ground showed that the size of the nebula increases over time. This leads to the assumption that the stellar outburst that formed the wings happened only 1200 years ago.
The central star in M2-9 is actually a pair of stars orbiting each other at a dangerously small distance. It is even possible for one star to be enveloped by the other. Presumably, the gravity of one star pulls gas away from its companion, surrounding the two suns in a thin disk and expanding far into space.
M2-9 is located 2100 light years away in the constellation of the Ophiuchus. The image was taken on August 2, 1997 with the Hubble Telescope's Wide Field and Planetary Camara 2. In the image, neutral oxygen appears red, singly ionized nitrogen is green, and doubly ionized oxygen is blue.
IC 3568 lies about 9000 light-years away in the constellation of Giraffe and is about 0.4 light-years across. It is an example of a round planetary nebula.
The eye-like appearance of NGC 6826. The bright green 'white of the eye' consists of gas that is believed to have once made up over half the star's mass. The hot star remnant at the center is one of the brightest remnants in planetary nebulae. NGC 6826 is 2200 light years distant in the constellation Cygnus.
NGC 3918 is found in the constellation Centaurus and is about 3000 light-years from us. Its diameter is about 0.3 light-years. It shows a roughly spherical 'outer envelope' but a stretched inner balloon, inflated by a fast wind blowing from the hot central star. This begins to break out of the spherical shell.
Hubble 5 is a notable example of a "butterfly" or bipolar nebula. The heat generated by fast winds causes the two wings to expand. Hubble 5 is 2200 light years away in the constellation Sagittarius.
Like NGC 6826, NGC 7009 has a bright central star at the center of a dark cavity surrounded by an elliptical rim of dense blue and red gas. The cavity and its rim are trapped in finely divided green barrel-shaped matter that encloses the star's former outer layers. A pair of red "handles" appear at a greater distance along the long axis of the nebula. The handles are low-density clouds of gas, each connected to the top of the cavity by a long jet of green matter. NGC 70009 is 1400 light years distant and found in the constellation Aquarius.
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