Physics Photo of the Week
October
15, 2009
The Trifid Nebula
Astronomy
students - Kesari Fleury, Dan Segal,
Marlon Cohn, Christina Grubb, and Madalyn Baldwyn - all helped
produce this vivid color photo of the Trifid Nebula, also known as
Messier 20 in early September, 2009. This object in Sagittarius
is a luminous "ball" of mostly hydrogen gas plus some veins of dust
that make the dark lanes against the pink background. This object
is in our own Milky Way Galaxy. It's luminosity is caused by
fluorescence of the hydrogen gas. Some very hot young stars near
the center emit strong ultraviolet radiation. The hydrogen clouds
absorb the ultraviolet then re-radiate it in the strong visible color
characteristic of hydrogen - mostly red. A more general
classification for this object is to call it an "emission nebula"
because the colors are discrete emission lines as opposed to broadband
radiation characteristic of stars. (See
PPOW for April 16, 2004 for a discussion of emission lines).
Such an emission nebula is also a place where stars are currently
forming. The hydrogen clouds collapse under their own force of
gravity, become denser and denser until they become dense enough to
trigger nuclear fusion of hydrogen into helium - thus forming new
stars. The stars in these emission nebulas are about 100 times
more massive than the Sun. Consequently they burn at much higher
temperatures than the Sun (30,000 K instead of 6,000 K) and emit much
ultraviolet radiation. The most famous example of an emission
nebula giving birth to young, hot stars is the Orion Nebula (PPOW
for Jan. 23, 2009, and PPOW
for Apr. 24, 2009).
The color image was obtained using a deep sky CCD camera on Warren
Wilson College's 8-inch portable telescope. The monochrome camera
is equipped with a set of red, green, and blue filters. The red,
green, and blue images are then combined by the students with special
software to produe the composite color image.
There will be no Physics Photo of the Week next week on October 23 due
to WWC's fall break. The next Physics Photo of the Week will be
published on October 30, 2009.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
