Page 26 - Curriculum Visions Dynamic Book

Butterfly Nebula
 This is the Butterfly Nebula NGC 2346. The nebula is about 2,000 light-years away from Earth in the direction of the constellation Monoceros.
It represents the spectacular “last gasp” of a binary star system at the nebula’s center. At the center of the nebula lies a pair of stars that are so close together that they orbit around each other every 16 days. This is so close that they appear to be just one star. One star is the hot core of a star that has ejected most of its outer layers, producing the surrounding nebula.
Astronomers believe that this star, when it evolved and expanded to
become a red giant, actually swallowed
its companion star in an act of stellar cannibalism. The resulting interaction
led to a spiraling together of the two stars, resulting in ejection of the outer layers of the red giant. Later, the hot star developed a fast stellar wind. This wind, blowing out into the surrounding disk, has inflated the large, wispy hourglass-shaped wings perpendicular to the disk. The total diametre of the nebula is about one-third of a light-year, or three trillion kilometres.
condensation To make something more concentrated or compact.
red giant A cool, large, bright star at least 25 times the diametre of our Sun.
stellar Wind The flow of tiny charged particles (called plasma) outward from a star.
Red giant stars
Small stars do not just fade away as they die. As the fuel begins to run out in a small star, the gases cannot oppose gravity, and the core contracts. That makes it heat up, and for a while even more energy reaches the outside. As a result, the last phase of a star is not a slow event, but one that is often dramatic.
As the outer regions of the star become heated, they expand. At this stage the star turns from a main-sequence yellow star and grows into a red giant star.
At the same time, the nuclear “ash” at the core, which is made of helium, may get so hot that the helium atoms fuse into carbon. Then, if the temperature is high enough, carbon and helium atoms can fuse to produce oxygen. So the death of a star also produces new elements.
Meanwhile, if the shell of the star has burned away all of its hydrogen to helium, the helium can then begin to fuse in this region too, and the whole process of creating heavier elements can also take place in the outer shell of the star.
The outer atmospheres of such a star may be cool enough to allow the condensation of some of the heavy elements into solid particles, creating grains of dust.
Planetary nebula
The force of gravity depends on a concentration of mass. With an enormously expanded shell of gases and dust, gravity becomes too weak to hold much of the dead star together, and much of it blows out of the star to form a violent stellar Wind (the same kind of thing as the solar wind, but vastly greater in amount).
 This is a picture of a dying star, NGC 6543, nicknamed the “Cat’s Eye Nebula.” You can see concentric gas shells, jets of high-speed gas, and unusual shock-induced knots of gas.
A fast stellar wind of gas blown off the central star created the elongated shell of dense, glowing gas. NGC 6543 is 3,000 light-years away in the northern constellation Draco.
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