APOD: A Sagittarius Triplet (2017 Jul 27)

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APOD: A Sagittarius Triplet (2017 Jul 27)

Postby APOD Robot » Thu Jul 27, 2017 4:06 am

Image A Sagittarius Triplet

Explanation: These three bright nebulae are often featured on telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula above and left of center, and colorful M20 near the bottom of the frame. The third emission region includes NGC 6559, right of M8 and separated from the larger nebula by a dark dust lane. All three are stellar nurseries about five thousand light-years or so distant. Over a hundred light-years across the expansive M8 is also known as the Lagoon Nebula. M20's popular moniker is the Trifid. Glowing hydrogen gas creates the dominant red color of the emission nebulae. In striking contrast, blue hues in the Trifid are due to dust reflected starlight. The colorful composite skyscape was recorded with two different telescopes to capture a widefield image of the area and individual close-ups at higher resolution.

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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Boomer12k » Thu Jul 27, 2017 6:22 am

Stunning image... . by coincidence I was looking at M8 and M20, M17, M16, M15, and others tonight in my new Celestron Evolution 6". Did not have the laptop and camera out, but maybe tomorrow night. I did a one star alignment, Altair, and then to Saturn, it was off to the top a bit, but not hard to find of course, but when I do a 2 star alignment it was in the eyepiece.

Great detail and colors!!!

My M20 with my 10" Meade LX200...
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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Ann » Thu Jul 27, 2017 6:35 am

Seeing a new picture of a familiar object - or a trio of familiar objects - can make you see things in a new way. Josep Drudis picture of the well-known Sagittarius Triplet, consisting of the Lagoon Nebula, the Trifid Nebula and NGC 6559, made me acutely aware of extended red nebulosities between the Lagoon Nebula and the Trifid Nebula. I could find one of these very faint nebulas in my software, namely the one to the upper left of the Trifid Nebula in Josep Drudis' image. It's called Sharpless 26. But the one to the upper right of the Trifid Nebula remains frustratingly nameless to me.

I searched for other pictures of the Lagoon and Trifid nebulas to see if I could spot these faint nebulas in other pictures, too. And indeed, in Éder Iván's picture, which is the second of the attachments below, the starry background has taken on a very, very faint red tinge between the Lagoon and the Trifid nebulas.

It is worth noticing that Josep Drudis quite obviously lives somewhere in the southern hemisphere, which is why his picture of the Sagittarius Triplet is "turned the wrong way" - well, to us northerners at least, it looks like that! :wink:

I was not familiar with Josep Drudis before I saw today's APOD, but he has taken many other fine astropictures aprt from this one. Just check out his picture of the Tarantula region in the Large Magellanic Cloud!

Ann
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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Ann » Thu Jul 27, 2017 6:36 am

Boomer12k wrote:Stunning image... . by coincidence I was looking at M8 and M20, M17, M16, M15, and others tonight in my new Celestron Evolution 6". Did not have the laptop and camera out, but maybe tomorrow night. I did a one star alignment, Altair, and then to Saturn, it was off to the top a bit, but not hard to find of course, but when I do a 2 star alignment it was in the eyepiece.

Great detail and colors!!!

My M20 with my 10" Meade LX200...
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So glad to see you have a new scope, Boomer! :D Keep taking pictures and post them here!

Ann
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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Catalina » Thu Jul 27, 2017 6:04 pm

Anyone have a explanation for the very well-defined, tightly convoluted, squiggly lines going across the front of NGC 6559? They are like dust lanes I have never seen.

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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby MarkBour » Thu Jul 27, 2017 7:35 pm

What a gorgeous image! I keep thinking that Charles Messier would have really loved being able to see these objects with this quality and resolution. He may have turned over from hunting for comets to further studying the objects he was ruling out.

https://en.wikipedia.org/wiki/Charles_Messier
Messier did his observing with a 100 mm (four inch) refracting telescope from Hôtel de Cluny (now the Musée national du Moyen Âge), in downtown Paris, France.


Catalina wrote:Anyone have a explanation for the very well-defined, tightly convoluted, squiggly lines going across the front of NGC 6559? They are like dust lanes I have never seen.

Pay them no mind. Just some DNA strands that are 10 light-years long. Who would be interested in that? 8-)

Seriously, I second the question. Bok globules? I have not seen anything that defined in previous images of NGC 6559.
Mark Goldfain

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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby rstevenson » Thu Jul 27, 2017 8:05 pm

Catalina wrote:Anyone have a explanation for the very well-defined, tightly convoluted, squiggly lines going across the front of NGC 6559? They are like dust lanes I have never seen.

That looks a lot like my signature. (Really, it does!) But I was never there, honest.

Rob

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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Ann » Thu Jul 27, 2017 8:55 pm

Catalina wrote:Anyone have a explanation for the very well-defined, tightly convoluted, squiggly lines going across the front of NGC 6559? They are like dust lanes I have never seen.


Here is my amateur interpretation of what we are seeing. Be warned.

First of all, we need to see several images of this area to get a better understanding of the objects there. So here goes:

NGC 6559. Photo: Adam Block.
NGC 6559. Credit and copyright: Jean-Charles Cuillandre.




















Take a look at these two pictures of NGC 6559. The way I understand it, NGC 6559 is the bright red arc-shaped emission nebula which is centrally placed in Jean-Charles Cuillandre's image. It's to the lower left in Adam Block's image. To the upper left of NGC 6559 in Jean-Charles Cuillandre's image, and to the upper right of of NGC 6559 in Adam Block's image, is a bright blue star which is tangled in convoluted dust lanes. This star is HD 165921. According to Simbad Astronomical Database, HD 165921 is a binary star consisting of O7V and B0V components.

So HD 165921 is a powerful star, which emits a lot of ultraviolet light. Even so, the red emission nebula that surrounds it is faint. My interpretation is that the stellar wind of HD 165921 has blown away much of the gas from the star's vicinity, so that there is relatively little gas there to ionize. Other powerful stars have done much the same thing: Check out this image of Orion and note the relative faintness of the Lambda Orionis nebula at Orion's "head".

But even though I believe that HD 165921 is located in an area where the "gas density" is low, I also believe that the dusty tendrils surrounding it (looking impressively blue in Jean-Charles Cuillandre's image) are dusty remnants of the gas cloud that HD 156921 were born from. Or... no. No, it's more likely that the tendrils of dust were produced much later, during some violent event involving one or both stars of HD 1565921 itself. Maybe the two components had a too-close encounter of the third kind? Maybe one of the stars ate one of its large planets, totally shattering it and spreading dust along its tattered magnetic lines?

Note the rectangular area of relative emptiness surrounding HD 165921, as if the bright binary star had blown out a "Spongebob Squarepants" cavity around itself. But the walls of this cavity are relatively smooth and regular, belying any truly violent event. Then again - those contorted dust lanes look "battle-scarred"!

NGC 2327. Photo: Catman46.
Fascinatingly, there is one convoluted string of dust that seems to connect HD 165921 with NGC 5965. Is it even possible that the connection is "real"? Could it be, is it possible, that HD 165921 and NGC 6559 are two different products of more or less the same dusty gas cloud? And could it be that the "umbilical cord" between them is the only connection that remains? Other nebulas also have dusty cords seemingly attached to them. Look at NGC 2327, the "head" of the Seagull Nebula, and the umbilical dust cord hangin out from the Seagull's "eye", HD 53367.

So where did the bright red arc-shaped nebula NGC 6559 come from?

NGC 6559. Photo: ESO.
Well, as you can see, the red arc of NGC 5965 seems to almost "embrace" a blue reflection nebula "below" (or "behind") it. There are two whitish stars plainly visible in the blue reflection nebula, as well as a lot of dust. In Jean-Charles Cuillandre's image you can see how the red emission nebula actually seems to encircle the blue reflection nebula in its entirety.

I believe that the blue reflection nebula is a site of ongoing star formation, so that the stars inside are very young. I would think that there are still more stars being born in there, perhaps behind the thick dust that can be seen to one side of the blue reflection nebula.

A region of star formation that is mostly blue in color means, to me, that the stars born here are of relatively low mass. There are no O-type stars here, and probably no very early B-type stars, either. Nevertheless, star formation is an energetic process. The combined heat, ultraviolet light, X-rays and other forms of energy produced by these young stars will push at the dust cloud that they were born from. So the dust cloud tries to expand. But as it does so, it runs into the strong wind and harsh ultraviolet light emitted by HD 165921, the O7V+B0V binary star.

In other words, I think that the bright red arc of NGC 5965 is a place where hydrogen is being piled up because it is pushed at from two directions, and it is becoming ionized by energetic processes working at it from both northwest and southeast.

IC 1274-1275. Photo: R Jay GaBany.
Now let's look at another fascinating object here, an emission nebula known as IC 1274. I believe that IC 1274 is the round pink nebula at far left in R Jay GaBany's image. There are a couple of blue stars inside it, and it seems to be surrounded by a blue "border". As you can see, there are a couple of dark dust towers in front of it, and to me it seems obvious that this dust is being evaporated away. The dusty wall connecting the two dark towers is smoking like a chimney! The stars doing the dust evaporation and providing the blue illumination are most likely the stars of IC 1274, or so I think anyway.

Well, those are my two cents! There is certainly a lot of dust and gas in this area, and different groups of young stars are affecting the dust and gas in different ways.

Ann
Last edited by Ann on Fri Jul 28, 2017 8:33 pm, edited 3 times in total.
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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Boomer12k » Thu Jul 27, 2017 11:06 pm

Ann wrote:
Boomer12k wrote:Stunning image... . by coincidence I was looking at M8 and M20, M17, M16, M15, and others tonight in my new Celestron Evolution 6". Did not have the laptop and camera out, but maybe tomorrow night. I did a one star alignment, Altair, and then to Saturn, it was off to the top a bit, but not hard to find of course, but when I do a 2 star alignment it was in the eyepiece.

Great detail and colors!!!

My M20 with my 10" Meade LX200...
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So glad to see you have a new scope, Boomer! :D Keep taking pictures and post them here!

Ann


Will do, Ann....
ENTUA,
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Re: APOD: A Sagittarius Triplet (2017 Jul 27)

Postby Ann » Sun Aug 06, 2017 7:31 pm

I just checked out this image in the Recent Submissions forum. I should have praised it more, because it's really striking, and it clearly reveals new aspects of this well-known triplet.

Ann
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