APOD: When Roses Aren't Red (2024 Feb 09)

[APOD Robot]

When Roses Aren't Red

Explanation: Not all roses are red of course, but they can still be very pretty. Likewise, the beautiful Rosette Nebula and other star forming regions are often shown in astronomical images with a predominately red hue, in part because the dominant emission in the nebula is from hydrogen atoms. Hydrogen's strongest optical emission line, known as H-alpha, is in the red region of the spectrum. But the beauty of an emission nebula need not be appreciated in red light alone. Other atoms in the nebula are also excited by energetic starlight and produce narrow emission lines as well. In this close-up view of the Rosette Nebula, narrowband images are mapped into broadband colors to show emission from Sulfur atoms in red, Hydrogen in green, and Oxygen in blue. In fact, the scheme of mapping these narrow atomic emission lines (SHO) into the broader colors (RGB) is adopted in many Hubble images of emission nebulae. This image spans about 50 light-years across the center of the Rosette Nebula. The nebula lies some 3,000 light-years away in the constellation Monoceros.

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[Ann]

Let's start with the APOD, even if it is large:

When Roses Aren't Red
Image Credit & Copyright: Tommy Lease (Denver Astronomical Society)

It's a handsome picture. The blue color in this mapped color image comes from doubly ionized oxygen, which represents a high level of excitation typically seen near very hot and energetic stars. In RGB images, the Rosette Nebula looks very red from ionized hydrogen alpha.


An even larger picture than the APOD - it's 5.9 MB - is so large that I hesitated to post it, but I'll do it anyway!

Isn't it glorious? Be sure to click to see the full size of it. Or, better yet, go to this page to see it.

Anyway. You can see Orion's Belt, the three blue stars in a row, a little below center and a bit to the right. An elongated red patch is hanging from the leftmost star in Orion's Belt - that's where the Horsehead Nebula rears his tiny head - and below that, there are two pink blobs. The largest, brightest and pinkest of them is the Orion Nebula.

Well, this thread should be about the Rosette Nebula. And you can see the Rosette Nebula in the upper left corner.

Note the difference between the Rosette Nebula and the Orion Nebula. While the Orion Nebula is pink and bright white in the center, the Rosette Nebula is red, not pink, and it is not brighter in the center. In fact, the light from the very center of the Rosette Nebula comes mostly from the star cluster, not from the nebulosity. Actually the Rosette Nebula itself is so faint that it is hard to see it through a telescope.

The Rosette Nebula with nebulosity in red and pink. Credit: Greg Polanski.

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A sketch of the Rosette Nebula, showing what the Rosette Nebula looks like through a telescope.

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Note! The Rosette Nebula is much larger than the Orion Nebula. The distance to the Rosette Nebula is 5,000 light-years, but the distance to the Orion Nebula is "only" some 1,500 light-years.

So the Rosette Nebula is much larger than the Orion Nebula. The Rosette is also much more attenuated, much fainter, and there is a hole at the center of it. Why? It is possible that the Rosette Nebula is definitely older than the Orion Nebula, so that the central stars have had much more time to eat away at the nebula and disperse it. But another explanation is that the cluster inside the Rosette Nebula, NGC 2264, is so much more energetic and powerful than the Trapezium cluster in Orion that it has dispersed its birth nebula so much more quickly.

After all, the Trapezium Cluster in Orion contains "only" one O-type star, Theta1 Orionis C, of spectral class O6V. But NGC 2244 contains at least five O-type stars, and the two hottest and brightest of them are spectral classes O4V and O5V.

To see what happens to the gas clouds that give birth to massive star clusters, consider the really massive Double Cluster of Perseus. Their age has been estimated at 12 million years. They undoubtedly contained several O-type stars when they were younger, but the O-type stars have either evolved into B-type supergiants or actually exploded as supernovas, although I haven't heard anything about supernova remnants in the Double Cluster.

So what happened to the mighty nebula that gave birth to this massive pair of star clusters? Well, the latest APOD that featured the Double Cluster actually showed us some nebulosity on the outskirts of the clusters. No other portraits of these mighty star clusters have been able to do that, as far as I know!

The Double Cluster in Perseus. Note the nebulosity.
Credit: Mårten Frosth

And there is an animal parade of dust pillars walking a dust rim in the Rosette Nebula - the panther is famous:

An animal parade in the Rosette Nebula. Credit: Ruben Barbosa.

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Got to go now!

Ann

[Chris Peterson]

And there is an animal parade of dust pillars walking a dust rim in the Rosette Nebula - the panther is famous:

I've shot this object in different ways, but what I like best is just H-alpha monochrome. Most of the activity in this nebula is from hydrogen, and I find that isolating just that really makes a lot of detail pop (including your animal parade). And yes, it's a big object. I had to shoot this as a 2x2 mosaic to even get this much, and there's still plenty outside the frame.
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[Ann]

And there is an animal parade of dust pillars walking a dust rim in the Rosette Nebula - the panther is famous:

I've shot this object in different ways, but what I like best is just H-alpha monochrome. Most of the activity in this nebula is from hydrogen, and I find that isolating just that really makes a lot of detail pop (including your animal parade). And yes, it's a big object. I had to shoot this as a 2x2 mosaic to even get this much, and there's still plenty outside the frame.
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Click to view full size image

Thank you for that image, Chris! I always appreciate it when you post your images here. And even though I absolutely love color images that flatter my particular sense of aesthetics, I can indeed appreciate black and white pictures too, when they bring out fascinating details that can be less obvious in color images.

There is an aspect of the Rosette Nebula that I wonder about. There is some sort of elegant gaseous swirls in the Rosette Nebula, see the wavy white line in my annotation of today's APOD:

What do you think that could be?

Ann

[Chris Peterson]

There is an aspect of the Rosette Nebula that I wonder about. There is some sort of elegant gaseous swirls in the Rosette Nebula, see the wavy white line in my annotation of today's APOD:

What do you think that could be?

I think it is pretty clearly a shock front. But what's driving that particular material isn't obvious. It is interesting to compare this region in both hydrogen and oxygen. We can clearly see areas that are stronger in one or the other, but that shocked region appears to be made up of both very uniformly. Maybe that means it's a very new structure and there hasn't been time for material to separate at all? I don't know, but it's a cool bit of the Rosette. There's obviously a lot of interesting stuff going on there.
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[Ann]

There is an aspect of the Rosette Nebula that I wonder about. There is some sort of elegant gaseous swirls in the Rosette Nebula, see the wavy white line in my annotation of today's APOD:

What do you think that could be?

I think it is pretty clearly a shock front. But what's driving that particular material isn't obvious. It is interesting to compare this region in both hydrogen and oxygen. We can clearly see areas that are stronger in one or the other, but that shocked region appears to be made up of both very uniformly. Maybe that means it's a very new structure and there hasn't been time for material to separate at all? I don't know, but it's a cool bit of the Rosette. There's obviously a lot of interesting stuff going on there.
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ha_o3.jpg

Thanks, Chris!

Ann