That's a fine picture!
The Christmas Tree cluster. Photo: ESO.
This general area, the Christmas Tree cluster, is one of my favorite sites of star formation in the sky. The Fox Fur Nebula is a part of the Christmas Tree cluster, but the Fox Fur is not easy to understand.
This enigmatic formation of gas and dust...
Enigmatic is the word. If Wikipedia can't shed much light on it, how can I? But at least I can show you a few pictures of this area and tell you what I see in them.
First off, in today's APOD the Fox Fur Nebula is rather brightly red at the same time as it is obviously very dusty. That in itself is strange. As a rule, dust structures either reflect the light of stars back at us, in which case they are usually bluish, or they block light from us, in which case they are brown or black. Ionized gas, on the other hand, is usually red. So why would a very dusty structure like the Fox Fur Nebula be extra red???
A clue can be found in the ESO image of the Christmas Tree cluster that I posted at left. Anyone who recognizes the Cone Nebula
should be able to spot it at bottom left. But where is the Fox Fur Nebula? It is located at upper right in the image, and as you can see, it is rather dark. The bluish reflection nebula below it is much brighter. The reflection nebula is lit up by a small cluster of young stars of spectral class B, which are not hot enough to ionize a red emission nebula, but whose blue light is scattered in the dust around them and reflected back at us. The ESO picture shows us that the Fox Fur Nebula is about the same rather dark red color as much of the rest of this area. So the difference between the blue reflection nebula and the red Fox Fur nebula is not so much that the Fox Fur is so anomalously red, but rather that the reflection nebula is so bright. It is in fact likely that there is red light inside the blue reflection nebula too, but it is "drowned out" by the scattered bright blue starlight there. So why isn't the Fox Fur Nebula bright blue too from reflected starlight? Because dust doesn't just reflect but also blocks starlight, and the dust in the Fox Fur Nebula blocks most of the blue light from the nearby reflection nebula.
The Christmas Tree Cluster. Image: Davide de Martin.
Let's look at another picture of the same area. This picture is oriented "upside down" relatively to the ESO image I posted earlier, so the Cone Nebula is at top. Also the color balance is different. The blue light is quite bright here, but the red light is rather muted and dull. Where is the Fox Fur Nebula? It is to the left of the bright star, S Mon or 15 Mon. In this picture, the Fox Fur nebula looks quite "thin". The blue light in the area is shining right through it. The Fox Fur nebula now looks quite a bit like the famous "Pillars of Creation"
, interconnected dark dusty outlines which fade out "at the bottom", where they slowly disappear into the background. I think it is true that much of the Fox Fur is quite "thin".
On the page
where I found this picture, it says:
The Fox Fur Nebula has a strange shape originate from fine interstellar dust reacting in complex ways with the energetic light and hot gas being expelled by the young stars.
The English here isn't perfect, but I agree with the message: The Fox Fur is being sculpted by energetic light coming from different directions from several stars in the area, and it is reacting to it in complex ways.
The Christmas Tree Cluster. Photo: R. Jay GaBany.
I'd like to show you one more picture of the same area. In this one, you find the Cone Nebula at right and the Fox Fur Nebula at left.
The Fox Fur is looking very
foxy here! Very elegant! But you can see that it is "thin". Blue light is shining through much of it.
In the right half of the image, however, there is a lot of yellow light peeking through. I'd say that is light associated with star formation. The dust in this part of the Christmas Tree cluster region is "thick", and new stars are forming there.
The Christmas Tree Cluster. Image credit: SIRTF/NASA/ESA
I can't resist showing you one more picture. This is an infrared image of the Christmas tree cluster. The Cone Nebula is at top, right above the bright pink-looking star. (The Cone Nebula sports a bright, but not brilliant, yellow-white "head".)
All the pink lights here are baby stars in various stages of formation. Most if not all are probably quite invisible in optical images.
Where is the Fox Fur Nebula? It is all but invisible. It is at lower left, below the large cavity which is blurrily lit up by pink light. But as I said, you can barely see the Fox Fur Nebula here.
We can draw a few conclusions. The Fox Fur Nebula is "thin". There is no star formation going on inside it at all. Its nature might be slightly similar to the Pillars of Creation, except that, unlike the Pillars of Creation, it is not a site of star formation. The Fox Fur Nebula consists of gas and dust, and the dust is being buffeted by strong stellar winds from different directions. Its color comes from the diffuse Ha emission which fills much of the entire region, but the Fox Fur Nebula is not particularly bright.
That's what I can say about it, I think.