Explanation:
Blown by fast winds from a hot, massive star,
this cosmic bubble is huge.
Cataloged as
Sharpless 308
it lies some 5,200 light-years away
in the constellation
Canis Major
and covers over 2/3 degree on the sky
(compared with 1/2 degree for the Full Moon).
That corresponds
to a diameter of 60 light-years at its estimated
distance.
The massive star itself, a
Wolf-Rayet star,
is the bright blue
one near the center of the nebula.
Wolf-Rayet stars have over 20 times the mass of the Sun and
are thought to be in a brief,
pre-supernova phase of massive star
evolution.
Fast winds from this Wolf-Rayet star create the bubble-shaped
nebula as they sweep up slower moving material from an earlier
phase of evolution.
The windblown nebula has an age of
about 70,000 years.
Relatively faint emission captured in the expansive image
is dominated by the glow of ionized oxygen atoms
mapped to bluish hues.
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