APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

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APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by APOD Robot » Tue Jun 07, 2022 4:05 am

Image NGC 6188: Dragons of Ara

Explanation: Do dragons fight on the altar of the sky? Although it might appear that way, these dragons are illusions made of thin gas and dust. The emission nebula NGC 6188, home to the glowing clouds, is found about 4,000 light years away near the edge of a large molecular cloud unseen at visible wavelengths, in the southern constellation Ara (the Altar). Massive, young stars of the embedded Ara OB1 association were formed in that region only a few million years ago, sculpting the dark shapes and powering the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. Joining NGC 6188 on this cosmic canvas, visible toward the lower right, is rare emission nebula NGC 6164, also created by one of the region's massive O-type stars. Similar in appearance to many planetary nebulae, NGC 6164's striking, symmetric gaseous shroud and faint halo surround its bright central star near the bottom edge. This impressively wide field of view spans over 2 degrees (four full Moons), corresponding to over 150 light years at the estimated distance of NGC 6188.

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Ann
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Re: APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by Ann » Tue Jun 07, 2022 8:50 am

I don't mind dragons 🐉 but I prefer stars! 🌟

The illuminating star of this entire skyscape, HD 150136, is a remarkable multiple star whose hottest component belongs to spectral class O3.5V!

NGC 6193 ESO Martin Pugh Robert Gendler Roberto Colombari.png
HD 150136 of NGC 6193. ESO/Martin Pugh/Robert Gendler/Roberto Colombari.
NGC 6188 and NGC 6193 by Joseph M Drudis.png
NGC 6193 (cluster) and NGC 6188 (nebula) by Joseph M. Drudis.
Wikipedia wrote about multiple star HD 150136:

All three (four, including HD 150135) of the brightest stars are massive luminous O class main sequence stars, 33-63 times as massive as the sun. They are around 10 times the size of the sun, but 6-8 times hotter and each is over 100,000 times as luminous. The primary star is the closest O3 star to Earth, 46,500 K, visually 18,000 times as bright as the sun, but because of its high temperature it is around three quarters of a million times more luminous including all wavelengths.
Wowzers! :D

And I may as well make use of all three attachments that I am allowed per post. So here is NGC 6193 and NGC 6188 by Rolf Wahl Olsen:

NGC 6193 NGC 6188 Rolf Wahl Olsen.png

Yeah. Stunning. Yeah. :thumb_up: :yes:

Ann
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Re: APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by beryllium732 » Tue Jun 07, 2022 11:07 am

Ann wrote: Tue Jun 07, 2022 8:50 am I don't mind dragons 🐉 but I prefer stars! 🌟

The illuminating star of this entire skyscape, HD 150136, is a remarkable multiple star whose hottest component belongs to spectral class O3.5V!

NGC 6193 ESO Martin Pugh Robert Gendler Roberto Colombari.png
HD 150136 of NGC 6193. ESO/Martin Pugh/Robert Gendler/Roberto Colombari.
NGC 6188 and NGC 6193 by Joseph M Drudis.png
NGC 6193 (cluster) and NGC 6188 (nebula) by Joseph M. Drudis.
Wikipedia wrote about multiple star HD 150136:

All three (four, including HD 150135) of the brightest stars are massive luminous O class main sequence stars, 33-63 times as massive as the sun. They are around 10 times the size of the sun, but 6-8 times hotter and each is over 100,000 times as luminous. The primary star is the closest O3 star to Earth, 46,500 K, visually 18,000 times as bright as the sun, but because of its high temperature it is around three quarters of a million times more luminous including all wavelengths.
Wowzers! :D

And I may as well make use of all three attachments that I am allowed per post. So here is NGC 6193 and NGC 6188 by Rolf Wahl Olsen:


NGC 6193 NGC 6188 Rolf Wahl Olsen.png

Yeah. Stunning. Yeah. :thumb_up: :yes:

Ann
Very cool! How come the pictures are so different? If we would be much nearer the nebula what would it look then? Would it be as colorful as the bluish orange picture?

I guess HD 150136 would have a very short life compared to our sun? Is HD 150136 the sole star the brighens up this nebula and gives it that particular look?

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Re: APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by orin stepanek » Tue Jun 07, 2022 1:31 pm

etacar_spitzer_c800.jpg
To Me; it looks like a nude dancer preforming in the center of a
strange audience; an elephant; bottom right; a giant fish upper left;
Yoda upper right; etc; etc!
Ngc6188_Robertson_960.jpg
Dragons & NGC6264
wp-content-uploads-2015-07-surprise-dog.jpg
My doggie friend telling us all about it! :mrgreen:
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Chris Peterson
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Re: APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by Chris Peterson » Tue Jun 07, 2022 2:32 pm

beryllium732 wrote: Tue Jun 07, 2022 11:07 am Very cool! How come the pictures are so different? If we would be much nearer the nebula what would it look then? Would it be as colorful as the bluish orange picture?
It would not matter how close we got, it would look just the same, and be a faint, barely detectable gray color (but larger, of course). All that would get brighter would the stars, not the nebula. Finally from inside the nebula, we'd not really see it at all, except as a slightly brighter night sky.
Chris

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Ann
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Re: APOD: NGC 6188: Dragons of Ara (2022 Jun 07)

Post by Ann » Tue Jun 07, 2022 2:59 pm

beryllium732 wrote: Tue Jun 07, 2022 11:07 am
Very cool! How come the pictures are so different? If we would be much nearer the nebula what would it look then? Would it be as colorful as the bluish orange picture?

I guess HD 150136 would have a very short life compared to our sun? Is HD 150136 the sole star the brighens up this nebula and gives it that particular look?

Let's begin by taking a look at the ESO/Robert Gendler image:


In my opinion, this picture was probably made using R, G and B filters. These filters react to light in ways that are somewhat similar to the color-sensitive R, G and B cones in our retinas. They can therefore be used to produce "natural" color images. However, the ESO/Gendler image undoubtedly also makes use of a hydrogen alpha filter, which reacts to a wavelength of 656 nm. To our eyes, this wavelength just looks red, but it is a specific wavelength that is produced as ultraviolet light from hot stars ionizes electrons. The Hα light of 656 nm is actually emitted as the electron rids itself of the extra energy it received and falls back to its ground state again.

If you don't use an Hα filter when you produce images of emission nebulas, you won't detect as much red light (because the Hα light is often somewhat faint). But to summarize, the ESO/Gendler image has almost certainly been produced using RGB filters, to create "natural" (but saturated) colors, and the Hα filter has been used to bring out a lot of red light in the nebulas.


Let's look at the image by Joseph M. Drudis:


Joseph Drudis may or may not have used RGB filters (I think he has), but more importantly, he has definitely used an Hα filter and almost certainly an OIII filter. An OIII filter detects light at 501 nm, (which is this color ███), and in a manner similar to Hα light, it is emitted where there is (extra rarefied) oxygen gas in the presence of hot stars. OIII represents a higher level of ionisation than Hα.

As you can see, the color of OIII is green. But it is often mapped as bluish cyan or blue, which is the case here. So in Joseph Drudis' image we see red Hα mixed with dust and bluish OIII closer to the hot stars in a much "clearer", much less dusty part of this nebula. And Drudis has "tilted" the nebula to make it look like a steep hill.


Let's look at Rolf Wahl Olsen's image:


I'd say that this is an OIII+Hα+SII image, perhaps with some RGB to bring out the color of the stars. The OIII has been mapped as royal blue. Hα is probably mapped as green, and SII is probably mapped as red (well, SII really is red). The orange color in the nebula may be a mixture of Hα, mapped as green, and SII, mapped as red. (Or else it's just the Hα that has been mapped as orange.)

What would these nebulas look like up close? Well, I believe that the "surface brightness" of these nebulas is very low, which is to say that we wouldn't see (much) color in them even up close. At best, we would see some green from the OIII.

As for HD 150136, it is a multiple star, and I believe that there are no less than four O-type components there. O-type (main sequence) stars are always very massive and very hot. They are like the Sun but much, much hotter, brighter and more massive. And yes, they are short-lived. The are not expected to live more than a few million years.

Ann
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