The Orion Nursery

 

The other night I spent about 30 minutes imaging the area around the Horse Head Nebula. This was the first time I had captured it, and I was relatively pleased with the results. The area is a fascinating example of the mechanisms involved with stellar formation.

At the center of the image is a blue giant star, Alnitak. This is the western most star in Orion's belt. This star has a mass 33 times that of our Sun and 20 times the radius. Its energy is predominately in the ultraviolet area of the spectrum. This UV light excites a region of hydrogen gas just to its upper left in the image, the Flame Nebula.

The Flame Nebula glows from the excited hydrogen gas. Through its center are lanes of dust, so dense. it blocks the light from several hundred new stars behind the cloud. The presence of these stars was detected by the Chandra X-ray telescope. However, to us, it adds the illusion of a dancing flame.

The red veil that runs from the lower left to Alnitak is a Hydrogen II, HII, area. It glows from the energy emitted from Sigma Orionis which is just off the bottom of the frame. The hard edge on the left side of this area is caused by another dust cloud which is in front of the HII area. We know this as there is an observable difference in stellar densities from the left and right side of the HII region, i.e. there are more visible stars on the right side of the image than the left side.

In the center of this red veil is the Horse Head Nebula. This is a very dense dust cloud which blocks out the glow of the HII region behind it. This is very challenging object visually as the red HII region is not easily seen unless the skies are very dark. It is picked up easier by the camera as it is more sensitive to the red wavelength light.

There are three more emission nebulas in the image, one below the flame and two to the upper right. All are indicated in the annotated image. These areas are interstellar gasses that are excited by stars within the cloud. These stars are typically very young and hot stars like Alnitak. 

This area is all part of the Orion B Molecular cloud which also includes Messier 42, or the Orion Nebula, imaged to the left. This whole area is the closest star forming area to us, only a mere 1,300 lightyears distance. What is not seen in these images but has been confirmed by larger space-based telescopes are the presence of circumstellar discs, which most likely contain protoplanetary objects. 

We tend to think of the heavens as relatively static, however, when you use a timescale of many millions of years, we start to understand the dynamic nature of our universe. Looking up at Orion is like looking through a hospital nursery window, only instead of babies, we see stars.

Clear skies.

RW