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NGC 2392 in 60 Seconds
Narrator (April Hobart, CXC): Stars like the Sun can become remarkably photogenic at the
end of their lives. A good example is NGC 2392, which is located about 4,200 light years
from Earth. NGC 2392, which is nicknamed the "Eskimo Nebula", is what astronomers call
a planetary nebula. This name, however, is deceiving because planetary nebulas actually
have nothing to do with planets. The term is simply a historic relic since these objects
looked like planetary disks to astronomers in earlier times looking through small optical
telescopes. Instead, planetary nebulas form when a Sun-like star uses up all of the hydrogen
in its core, which our Sun will in about 5 billion years from now. When this happens,
the star begins to cool and expand, increasing its radius by tens to hundreds of times its
original size. Eventually, the outer layers of the star are swept away by a slow and thick
wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000
degrees Celsius, and is ejecting its outer layers in a fast wind traveling 6 million
kilometers per hour. The radiation from the hot star and the interaction of its fast wind
with the slower wind creates the complex and filamentary shell of a planetary nebula. Eventually
the central star will collapse to form a white dwarf star. X-ray data from NASA's Chandra
X-ray Observatory show the location of million-degree gas near the center of NGC 2392. Data from
the Hubble Space Telescope reveal the intricate pattern of the outer layers of the star that
have been ejected. Taken together, these data from today's space-based telescopes provide
us with spectacular views of planetary nebulas that our scientific ancestors - those that
thought these objects were associated with planets -- probably could never have imagined.