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Astronomical Observatory: Cool Images

Images: Orion Nebula

M42 Orion Nebula

The Orion Nebula is about 1600 light-years away, which is 10.3 million times the distance between the Earth and the sun. This is equivalent to about 25 quadrillion miles! The dimensions of the image are 9.0 × 8.3 light-years.

The Orion Nebula is actually at the front of what is called a giant molecular cloud (GMC) complex. These GMC’s contain molecular hydrogen, which is two hydrogen atoms bound together in a single compound. The center of the Orion Nebula contains massive, hot, blue stars whose temperatures range from roughly 10,000 K to 40,000 K, which translates to a range of 18000° F to 72000° F. This is roughly 2.5 to 7 times the temperature of the sun. These hot stars also heat up the surrounding nebula to 10,000 K and emit enough energy to eject the single electron in the hydrogen atoms surrounding the stars (this process is called ionization). After the electrons have been ejected, most of them will recombine with the ionized hydrogen. When this happens, the electrons eventually emit light of a characteristic wavelength of 656.2 billionths of a meter, which corresponds to red light. This is the cause of the red color that is visible in the vicinity of the blue stars. Regions in space that emit this characteristic wavelength, called H-alpha, are labeled HII regions. The Orion Nebula is just one of many HII regions in the Milky Way galaxy. Astronomers have even observed HII regions in other galaxies.

In addition to emitting beautiful red light, the Orion Nebula is a place of active star formation. The ultraviolet radiation from the blue stars causes the surrounding HII region to expand into the molecular cloud, which compresses it. This process of gas compression is what makes stars form – if enough mass is initially present, that mass will be significantly contracted, giving rise to stronger gravitational attraction and more kinetic energy to fuse the mass into stars. Astronomers theorize that a recent wave of compression triggered a new generation of star birth in the nebula, which appear as small, faint, red dots in the bottom half of the image.

Not only does the Orion Nebula contain hydrogen, but it is also surrounded by dust grains, which dim the starlight that we see from Earth, a phenomenon called extinction. The visible effects of these dust grains can be seen in the dark lanes that seem to be cutting into the nebula. These dark lanes are so dense that they block a large majority of the visible light that hits them. Amazingly, the grains that make up the dust clouds are much smaller than common household dust – the smallest dust grains have a radius of around 2 millionths of a meter! They are called polycyclic aromatic hydrocarbons. Even though the dust grains absorb a lot of visible light, they do not absorb nearly as much light of longer wavelengths, such as infrared light. In fact, the currently-forming stars in the nebula (the small, red dots in the image) can only be seen through an infrared filter, which can “see” through the dust in the nebula to reveal the stars that are blocked by dust.

Additional information on and images of the Orion Nebula can be found at the SEDS web site, and a "fly-through" movie of the Orion Nebula was made by the San Diego Supercomputing Center.

Processing details:
The data were taken with the Calvin-Rehoboth Robotice telescope on March 2, 2005. In the image above, the blue component is the image taken in the B filter, the green component is the image taken in the V filter, and the red component is a combination of the H alpha image (showing the emission line of the nebula) and the infrared image (showing stars hidden by dust).

North field: (J2000 coordinates 5h 35m 29.0s -5° 12’ 56.0”)
Filter Number of Exposures Exposure Time (s)
B
5
60
V
5
60
R (narrowband)
4
30
I
5
30
H alpha
3
300

South Field (J2000 coordinates 5h 35m 29.0s -5° 25’ 56.0”)
Filter Number of Exposures Exposure Time (s)
B
10
5
V
10
5
R (narrowband)
15
5
I
10
5
H alpha
15
30


Text and image made by student Andrew Butler as part of an Astr212 Honors project.


Content updated 2005 May 8

 

 

 

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