Explanation:
Gorgeous spiral
galaxy M33 seems to have more than its fair share
of bright emission nebulae.
In fact, narrow-band and broad-band
image
data are combined in this beautifully detailed composite to trace
the reddish emission nebulae, star forming
HII regions,
sprawling along loose spiral arms that wind toward the galaxy's core.
Historically of
great interest to astronomers, M33's
giant HII regions are some of the
largest known stellar nurseries -
sites
of the formation of short-lived but very
massive
stars.
Intense ultraviolet radiation from the luminous, massive stars ionizes
the surrounding gas and ultimately produces the characteristic red glow.
Spanning over 50,000 light-years and a prominent member of the
local group of
galaxies, M33 is also known as the
Triangulum Galaxy.
It lies about 3 million light-years distant.
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