Astronomy Picture of the Day

Curious Cometary Knots in the Helix Nebula

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#106419 by @ 14.04.2008 00:00 - nach oben -
Curious Cometary Knots in the Helix Nebula


What causes unusual knots of gas and dust in
planetary nebulas?

Seen also in the
Ring Nebula, the
Dumbbell Nebula and the
Eskimo Nebula,
the knots' existence was not initially predicted and their origins
are still not well understood.

Pictured above is a fascinating image of the
Helix Nebula by the
Hubble Space Telescope
showing tremendous detail of its mysterious gaseous knots.

The above cometary knots have masses similar to the Earth but have radii typically several times the orbit of Pluto.

One hypothesis
for the fragmentation and evolution of the knots includes existing gas being
driven out
by a less dense but highly energetic
stellar wind
of the central evolving star.

The Helix Nebula
is the closest example of a
planetary nebula
created at the end of the
life of a Sun-like star.

The Helix Nebula, given a technical designation of NGC 7293, lies about 700
away towards the
constellation of

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