The spiral galaxy NGC 6946 (lower left,
shown in a false color
ground-based image) lies at a distance of 17 million light years.
Adjacent to it's bright northern spiral arm is a bright
source with characteristics of an extremely bright remnant of a
supernova explosion. But astronomers have learned that the object
actually is debris from two or more supernovas slamming together
in a cosmic collision.
The Hubble Space
Wide Field and Planetary Camera 2 image of the region, shown at
upper right, resolves the source into several interlocking loops
of emission. Most of the light comes from a small crescent
of emission at the lower right in the Hubble image, where the
expanding shell from a relatively recent supernova explosion is
plowing into an older, larger shell from a previous explosion.
Astronomers have never seen this phase of such an
This material was presented to the American Astronomical Society
meeting in Winston-Salem, NC, on June 10, 1997.
Image credits: Lower left:
William Blair (The Johns Hopkins University) and NOAO/Kitt
Peak National Observatory.
William Blair, JHU.
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