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colourful image from the Hubble Space Telescope shows the collision of two
gases near a dying star. Astronomers have dubbed the tadpole-like objects
in the upper right-hand corner "cometary knots" because their glowing heads
and gossamer tails resemble comets. Although astronomers have seen gaseous
knots through ground-based telescopes, they have never seen so many in a
single nebula.
Hubble captured thousands of these knots from a doomed star in the Helix
nebula, the closest planetary nebula to Earth at 450 light-years away
in the constellation Aquarius. Each gaseous head is at least twice the
size of our solar system; each tail stretches 100 billion miles, about
1,000 times the Earth's distance to the Sun. The most visible gaseous
fragments lie along the inner edge of the star's ring, trillions of miles
from the star at its center. The comet-like tails form a radial pattern
around the star like the spokes on a wagon wheel. Astronomers have seen
the spoke pattern using ground-based telescopes, but Hubble reveals for
the first time the sources of these objects.
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Astronomers
theorize that the gaseous knots are the results of a collision between gases.
The doomed star spews the hot gas from its surface, which collides with
the cooler gas that it had ejected 10,000 years before. The crash fragments
the smooth cloud surrounding the star into smaller, denser finger-like droplets,
like dripping paint. Astronomers expect the gaseous knots, each several
billion miles across, to eventually dissipate into the cold blackness of
interstellar space.
The red light depicts nitrogen emission ([NII]
6584A); green, hydrogen (H-alpha, 6563A); and blue, oxygen (5007A).
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