APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

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APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by APOD Robot » Fri Sep 07, 2012 4:06 am

Image IC 4628: The Prawn Nebula

Explanation: South of Antares, in the tail of the nebula-rich constellation Scorpius, lies emission nebula IC 4628. Nearby hot, massive stars, millions of years young, radiate the nebula with invisible ultraviolet light, stripping electrons from atoms. The electrons eventually recombine with the atoms to produce the visible nebular glow, dominated by the red emission of hydrogen. At an estimated distance of 6,000 light-years, the region shown is about 250 light-years across, spanning an area equivalent to four full moons on the sky. The nebula is also cataloged as Gum 56 for Australian astronomer Colin Stanley Gum, but seafood-loving astronomers might know this cosmic cloud as The Prawn Nebula.

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by emc » Fri Sep 07, 2012 10:04 am

Beautiful! Lot of detail… lots of hydrogen.

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by merryjman » Fri Sep 07, 2012 11:13 am

I like the image, and I do appreciate the work you do to give us one of these every day, but why do you guys keep recycling old captions?? This is the same caption as the 2006 image of the same nebula...

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by starsurfer » Fri Sep 07, 2012 11:15 am

Amazing image, you really get the impression that there is a lot of energy and activity in this area what with all the energetic and luminous clusters. It's so nice to see something southern on APOD! :D

Ed Everett

Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Ed Everett » Fri Sep 07, 2012 1:12 pm

What is the name of the old man wearing glasses and with a bushy beard?
Just left of the center of the picture and looking toward the west.

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Chris Peterson » Fri Sep 07, 2012 1:37 pm

merryjman wrote:I like the image, and I do appreciate the work you do to give us one of these every day, but why do you guys keep recycling old captions?? This is the same caption as the 2006 image of the same nebula...
It's not the same caption. It is based on the 2006 caption (which is reasonable, since it's the same object). But the two captions differ where they describe the details of the images themselves.
Chris

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Peeratz » Fri Sep 07, 2012 3:03 pm

Ed Everett wrote:What is the name of the old man wearing glasses and with a bushy beard?
Just left of the center of the picture and looking toward the west.
Looks kinda like Galileo with his glasses on (if he had any) :)
http://www.crystalinks.com/galileo.html

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Ann » Fri Sep 07, 2012 4:47 pm

All day I've been meaning to comment on this great picture - thanks for creating the image, Marco Lorenzi! - but I have been busy and tired and scatter-brained and I haven't had access to my software and....

I didn't recognize the nebula or the cluster, but the picture looks very suggestive. The very fact that there's a large emission nebula there is fascinating. Emission nebulae aren't all that common, and moderately unreddened, obvious ones are less common still. Not all young star clusters have them. For example, the Double Cluster in Perseus, which contain large numbers of hot bright stars and are believed to be about five million years, lack any nebulosity. On the other hand, NGC 6559 in Sagittarius, which does not contain any obvious O stars, does have a moderately bright nebular arc and a large, faint emission nebula. And just think of NGC 7000, the North America Nebula, which seems unrelated to any of the hot blue stars that are seen "in" it or near it. There are probably various reasons for the presence or absence of emission nebulae near hot stars: the stars may have "blown away" all the gas, for example, or two gas clouds may be violently colliding for other reasons than the wind and brilliance of hot stars.

So what causes the emission nebula in this case? Is it the stars themselves, or is it some "background factor" of some sort? Maybe a past supernova explosion, although the shape of the nebula doesn't seem right for that? A moderately nearby but separate powerful cluster whose wind makes the gas collide violently with the surrounding interstellar medium?
NGC 6231 on the right and IC 4628 and Cr 316 at left.
Photo: Michael A. Stecker.
After getting access to my software, I'd say that a combination of ultraviolet light from the hot blue stars in the scattered cluster in this picture (called Collinder 316), plus the strong wind and ultraviolet from moderately nearby, massive young open cluster NGC 6231 seems like the most probable reason for the emission nebula. That is because Collinder 316 and emission nebula IC 4628 are like extensions of NGC 6231.
APOD Robot wrote:
Nearby hot, massive stars, millions of years young, radiate the nebula with invisible ultraviolet light, stripping electrons from atoms.
This piqued my interest. How young are the stars of Collinder 316? If they are hot enough to ionize the hydrogen gas in the vicinity and create an appreciable emission nebula, then they really can't be very many million years old.

A clue may be found in the estimated age of NGC 6231, the compact nearby cluster.
http://en.wikipedia.org/wiki/NGC_6231 wrote:
This cluster is estimated about 3.2 million years old
It seems likely that NGC 6231 and Collinder 136 are related. In my (amateur) opinon, it seems likely that NGC 6231 came first, and Collinder 136 was created in a wave of secondary star formation. If so, Collinder 136 is younger than NGC 6231.

Take a look at Marco Lorenzi's fine APOD again. The "moderately single-looking" brightish blue star at six o'clock is an evolved star star, HD 152667, possibly similar to Alnilam in Orion's Belt, according to my software. However, the small clustering of small stars to the upper right of HD 152667 is centered on what my software describes as a star of spectral class O7. If it is really a star of spectral class O7, then it is definitely hot enough to ionize an emission nebula. What's more, the small blue star directly above HD 152667, situated in the middle of the brightest part of the nebula and possibly the chief source of ionization, HD 152723, is also described by my software as a star of spectral class O7. These two O7 stars are likely younger than 3.2 million years.

What a fine and fascinating APOD this is!

Ann
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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Psnarf » Fri Sep 07, 2012 5:27 pm

In the full-size image, there are regions toward the left edge where the background stars appear less dense than on the right side beyond the hydrogen. Is that because there are dark dust lanes partially obscuring the background stars?

[They made up the word 'prawn' to avoid the wacky phrase 'jumbo shrimp'.]

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Chris Peterson » Fri Sep 07, 2012 5:41 pm

Image
Psnarf wrote:[They made up the word 'prawn' to avoid the wacky phrase 'jumbo shrimp'.]
I just figured it was the hypothesized origin of the aliens (aka "prawns") in District 9.
Chris

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Psnarf » Fri Sep 07, 2012 5:56 pm

Er, scratch that! I just learned about the open clusters NGC6231, NGC6242, Collinder 316 and Trumpler 24 that are nearby within the asterism Scorpius.

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by TNT » Fri Sep 07, 2012 10:13 pm

Hey, I'm one of those seafood-loving astronomers! :mrgreen:
The following statement is true.
The above statement is false.

rghoeing@buffalo.edu

Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by rghoeing@buffalo.edu » Fri Sep 07, 2012 11:54 pm

The "Prawn" nebula? Who came up with this ridiculous designation? Is Gum not deserving enough? The last thing we need is a cutesy sky...

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Boomer12k » Sat Sep 08, 2012 1:14 am

Oooooooo, Prawns and Chips..... :D


Nice Nebula...I noticed "the man with the glasses too"...


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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Chris Peterson » Sat Sep 08, 2012 1:36 am

rghoeing@buffalo.edu wrote:The "Prawn" nebula? Who came up with this ridiculous designation? Is Gum not deserving enough? The last thing we need is a cutesy sky...
"Gum" is just a catalog. "Gum 56" is a catalog designation for this object (IC 4628 is a more common one). "Prawn Nebula" is a name... which is different from a catalog number. Like the way we also call Messier 51 the Whirlpool Galaxy. FWIW, Gum 12 is often called the "Gum Nebula".

I think this image is showing much more than just the Prawn Nebula, including as well a good chunk of the large nebulous region around it.
Chris

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Re: APOD: IC 4628: The Prawn Nebula (2012 Sep 07)

Post by Moonlady » Sat Sep 08, 2012 2:55 am

Chris Peterson wrote:
Image
Psnarf wrote:[They made up the word 'prawn' to avoid the wacky phrase 'jumbo shrimp'.]
I just figured it was the hypothesized origin of the aliens (aka "prawns") in District 9.

After watching the movie I support your hypothesis! And I assume that there are also living cats...