APOD: The Dark Doodad Nebula (2024 Jun 25)

[APOD Robot]

The Dark Doodad Nebula

Explanation: What is that strange brown ribbon on the sky? When observing the star cluster NGC 4372, observers frequently take note of an unusual dark streak nearby running about three degrees in length. The streak, actually a long molecular cloud, has become known as the Dark Doodad Nebula. (Doodad is slang for a thingy or a whatchamacallit.) Pictured here, the Dark Doodad Nebula sweeps across the center of a rich and colorful starfield. Its dark color comes from a high concentration of interstellar dust that preferentially scatters visible light. The globular star cluster NGC 4372 is visible as the fuzzy white spot on the far left, while the bright blue star gamma Muscae is seen to the cluster's upper right. The Dark Doodad Nebula can be found with strong binoculars toward the southern constellation of the Fly (Musca).

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[Ann]

Note how the Doodad is leaking smoke along its entire length!

The Dark Doodad Nebula. Image Credit & Copyright: Martin Pugh & Rocco Sung

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Note in particular the dusty gusts of smoke that seem to surround globular cluster NGC 4372. Note the small blue foreground star on the right "corner" of NGC 4372 that seems to "intrude" on the globular and actually somewhat dim it by its own faint bluish reflection nebula.

Well, now take a look at a real closeup of NGC 4372 by Velimir Popov and Emil Ivanov:

NGC 4372. Credit: Velimir Popov and Emil Ivanov

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Take a look at the full size of Velimir Popov's and Emil Ivanov's image. Can you see a population of small blue stars in globular cluster NGC 4372? They are blue horizontal branch stars, and they are found in many globulars. But can you see that there are more blue stars in the "top half" of NGC 4372 (as shown in this image) than in the "bottom half"?

In my opinion, the "bottom half" of NGC 4372 is more dust-reddened by smoke from the Dark Doodad than the "top half" of this globular! That's why we see fewer small blue stars there. So we need the old woman tossed up in a blanket to brush the cobwebs from the sky, if we want a clearer view of NGC 4372!

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Unless we like the cobwebs of the sky, of course! They are our galaxy's incubators of new stars, and without these dark clouds, our galaxy would simply "wither and die"! Although it must be said that no star formation is visible in the Dark Doodad. But other dark clouds in the Milky Way are full of little star babies!

Star babies in the dark cloud of NGC 2264. Credit:NASA/JPL-Caltech/P.S. Teixeira

Hush baby, don't cry! You're going to be a star when you grow up. And you will have little planet babies of your own.

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Ann

[Deathfleer]

How large is a piece of the dust. Is it hot? If not, then there is no chance of it to conglomerate and form a star.

[Ann]

How large is a piece of the dust. Is it hot? If not, then there is no chance of it to conglomerate and form a star.

Dust (and gas) needs to be cold - really very cold - in order to for gravity to make it sink into its own gravity well and become concentrated enough to eventually form a star.

If the dust (and gas) is too hot, it will just disperse or move around turbulently.

Ann

[Chris Peterson]

How large is a piece of the dust. Is it hot? If not, then there is no chance of it to conglomerate and form a star.

The dust size follows some kind of power law distribution. The smallest will be just a few molecules, the largest a few tens of micrometers. The temperature of the dust depends on its material properties and proximity to energy sources. It can be as low as perhaps 10 K, and then or twenty times that close to a bright star. I think here we might be seeing something on the order of 100 K (say, -100 to -200 degrees C).

Dust doesn't come together to form stars. Gas comes together (there is vastly more gas here than dust, we just can't see it in visible light). Dust provides a kind of catalyst to help that process, in a way not yet fully understood.

[Chris Peterson]

Pictured here, the Dark Doodad Nebula sweeps across the center of a rich and colorful starfield. Its dark color comes from a high concentration of interstellar dust that preferentially scatters visible light.

While there is a little bit of scatter around the blue star and perhaps a few other brighter stars, the brown color we're seeing here is from the innate color of the dust, and is primarily a consequence of reflected light, not scattered light.

[Roberto]

Doodad's used to be tasty snacks as well.