APOD: RCW 85 (2024 Jun 14)

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APOD: RCW 85 (2024 Jun 14)

Post by APOD Robot » Fri Jun 14, 2024 4:05 am

Image RCW 85

Explanation: From the 1960 astronomical catalog of Rodgers, Campbell and Whiteoak, emission region RCW 85 shines in southern night skies between bright stars Alpha and Beta Centauri. About 5,000 light years distant, the hazy interstellar cloud of glowing hydrogen gas and dust is faint. But detailed structures along well-defined rims within RCW 85 are traced in this cosmic skyscape composed of 28 hours of narrow and broadband exposures. Suggestive of dramatic shapes in other stellar nurseries where natal clouds of gas and dust are sculpted by energetic winds and radiation from newborn stars, the tantalizing nebula has been called the Devil's Tower. This telescopic frame would span around 100 light-years at the estimated distance of RCW 85.

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Ann
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Ann » Fri Jun 14, 2024 6:18 am

This is a mysterious picture.


RCW is a region of star formation, and you can easily see where the baby stars are located. Their pale bluish light peeks through an opening in the molecular cloud at upper right in the APOD.

But what is that bright star (at left) doing there???

That star looks like it is a part of the nebulosity. Note that it appears to be located in a cavity in the molecular cloud, which is what we expect from hot massive stars. Also note that the area around the star appears to be brighter than the "tunnel" to the right of it, as if the light of the stars was lighting up its surroundings.

And yet, it also looks as if the star does not belong there. Considering how bright it looks compared with the molecular cloud, it doesn't affect its surroundings as much as it should if it was a hot bright star located inside the nebulosity.

Consider NGC 2264, a region of star formation which has spawned one very hot bright star, 15 Mon, and see how much it is affecting its surroundings:

NGC 2264 Bach Zoltan.png
NGC 2264 with bright star 15 Mon. Credit: Bach Zoltan.

Note the cavity that 15 Mon has carved around itself. Also note all the gaseous structures pointing at 15 Mon: There is the Cone Nebula at left, a bright red arc at right and the Fox Fur Nebula below 15 Mon. Also note all the other, less massive stars that are found in the vicinity of 15 Mon.

The bright star in the molecular cloud of RCW 85 is located in what might be described as "a sort of cavity". But the nebulosity around it appears to be mostly unaffected by the star. Yes, there is a smallish red "pillar" to the lower right of it, but this pillar does not stand out compared with all the other nebular structures. The molecular cloud as a whole does not seem to pay much attention to the presence of that star. Also the star is "lonely" and not surrounded by any "cluster siblings".

I checked the star, HD 125158, with Simbad. It turns out that HD 125158 is a modest star of spectral class A5 or A7, an Altair if you will, at a well-defined Gaia distance of some 150 light-years and a luminosity of some 14 times solar. There is no way that such a modest star can strongly affect a large molecular cloud like RCW 85! Especially since the distance to RCW 85 is more like some 6,000 light-years!!!

Case closed, right? Not quite. Because there are other pictures where the star, HD 125158, looks for all the world as if it was really involved with the nebulosity of RCW 85. Take a look at this gorgeous image by Mark Hanson:

RCW 85 and HD 125158 Mark Hanson.png
RCW 85 and HD 125158. Credit: Mark Hanson.


Just look at all the tattered nebulosity surrounding the star in Mark Hanson's picture! It looks for all the world as if HD 125158 belonged inside an extension of the molecular cloud of RCW 85, and yet that's impossible! I'm stumped.


An interesting feature of RCW 85 is its bright and very well-defined rim:


Such a bright rim of a molecular cloud must be sculpted by a hot bright star not too far from the cloud. And Mark Hanson has identified the star responsible for sculpting the rim:

Ann
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Christian G. » Fri Jun 14, 2024 12:19 pm

The top section reminds me of a similar one in the Eagle Nebula, both filled with star births:
rcw 85.png
eagle.jpg
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Re: APOD: RCW 85 (2024 Jun 14)

Post by sp0ck » Fri Jun 14, 2024 2:41 pm

Ann, I *do* enjoy your in depth reviews.

I just cannot help but see one the the Star Wars Imperial guards.
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Lee » Fri Jun 14, 2024 3:03 pm

"I just cannot help but see one the the Star Wars Imperial guards" (sp0ck)

I see a panther jumping across a volcano.

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Re: APOD: RCW 85 (2024 Jun 14)

Post by ZubenLGenubi » Fri Jun 14, 2024 3:36 pm

I dub thee "The Cookie Monster Nebula".

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Re: APOD: RCW 85 (2024 Jun 14)

Post by Sam » Fri Jun 14, 2024 3:39 pm

Lee wrote: Fri Jun 14, 2024 3:03 pm "I just cannot help but see one the the Star Wars Imperial guards" (sp0ck)

I see a panther jumping across a volcano.
https://idiotic-hat.blogspot.com/2015/06/a-ducky-and-horsie.html wrote:“Aren't the clouds beautiful? They look like big balls of cotton... I could just lie here all day, and watch them drift by... If you use your imagination, you can see lots of things in the cloud formations... What do you think you see, Linus?"
"Well, those clouds up there look like the map of the British Honduras on the Caribbean... That cloud up there looks a little like the profile of Thomas Eakins, the famous painter and sculptor... And that group of clouds over there gives me the impression of the stoning of Stephen... I can see the apostle Paul standing there to one side..."
"Uh huh... That's very good... What do you see in the clouds, Charlie Brown?"
"Well, I was going to say I saw a ducky and a horsie, but I changed my mind!”
― Charles M. Schulz, The Complete Peanuts, Vol. 5: 1959-1960
Quolheleth wrote:https://en.wikipedia.org/wiki/Ecclesias ... statements.
The first belongs to Qoheleth as the prophet, the "true voice of wisdom",[22] which speaks in the first person, recounting wisdom through his own experience. The second voice belongs to Qoheleth as the king of Jerusalem, who is more didactic and thus speaks primarily in second-person imperative statements. The third voice is that of the epilogist (i.e., the writer of the epilogue), who speaks proverbially in the third person.
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Avalon » Sat Jun 15, 2024 2:13 am

Are the "rays" that appear to be emitted from the top edges of the red cloud from energy escaping or light as crepuscular rays or ?

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Ann
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Ann » Sat Jun 15, 2024 5:08 am

Avalon wrote: Sat Jun 15, 2024 2:13 am Are the "rays" that appear to be emitted from the top edges of the red cloud from energy escaping or light as crepuscular rays or ?

Well, light is energy too! :wink:


What we see coming out of that opening in the RCW 85 molecular cloud is certainly light. It is visible light as well as infrared light. We do expect to see infrared light from regions of star formation. We see light from baby stars, but because there are many dust particles in these clouds, the light gets reddened, some of it to infrared wavelengths.


The light coming out of the opening of the dust cloud of RCW 85 does not appear to be tremendously reddened, but it is certainly somewhat reddened.

We should probably consider it to be a reflection nebula, where light is reflected and scattered by dust grains.


We don't see the newborn stars of RCW 85, but we can see some of their reflected light.

Crepuscular rays are "widening light pillars" that emerge from holes in a cloud cover:


We don't really see any crepuscular rays in RCW 85. We possibly see some pillar-shaped shadow, so-called anticrepuscular rays, as light from the the opening in RCW 85 is blocked in places by protruding extensions of the cloud.

Ann
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Re: APOD: RCW 85 (2024 Jun 14)

Post by Christian G. » Sat Jun 15, 2024 11:11 am

Ann wrote: Sat Jun 15, 2024 5:08 am
Avalon wrote: Sat Jun 15, 2024 2:13 am Are the "rays" that appear to be emitted from the top edges of the red cloud from energy escaping or light as crepuscular rays or ?

Well, light is energy too! :wink:


What we see coming out of that opening in the RCW 85 molecular cloud is certainly light. It is visible light as well as infrared light. We do expect to see infrared light from regions of star formation. We see light from baby stars, but because there are many dust particles in these clouds, the light gets reddened, some of it to infrared wavelengths.


The light coming out of the opening of the dust cloud of RCW 85 does not appear to be tremendously reddened, but it is certainly somewhat reddened.

We should probably consider it to be a reflection nebula, where light is reflected and scattered by dust grains.


We don't see the newborn stars of RCW 85, but we can see some of their reflected light.

Crepuscular rays are "widening light pillars" that emerge from holes in a cloud cover:


We don't really see any crepuscular rays in RCW 85. We possibly see some pillar-shaped shadow, so-called anticrepuscular rays, as light from the the opening in RCW 85 is blocked in places by protruding extensions of the cloud.

Ann
I was under the impression that part of what we see coming out of the top edges was gas being dispersed by hidden newborn stars (as per my comparaison above with one of the Eagle Nebula's pillars) - could it be?

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Re: APOD: RCW 85 (2024 Jun 14)

Post by Ann » Sat Jun 15, 2024 1:00 pm

Christian G. wrote: Sat Jun 15, 2024 11:11 am
Avalon wrote: Sat Jun 15, 2024 2:13 am Are the "rays" that appear to be emitted from the top edges of the red cloud from energy escaping or light as crepuscular rays or ?

I was under the impression that part of what we see coming out of the top edges was gas being dispersed by hidden newborn stars (as per my comparaison above with one of the Eagle Nebula's pillars) - could it be?
Sorry! I misunderstood (and it was my fault).

It is quite correct to compare RCW 85 with the tallest pillar in the Eagle Nebula.


So, yes. Hot stars are slowly eating away both RCW 85 and the Pillars of Creation from outside. But indeed, these structures are also being eaten away from inside, because the stars that have formed inside them also blow a non-negligible stellar wind, which carves cavities inside their birthplaces. Also star formation is often a messy process, where the baby stars act up in different ways and spit out jets.

I'd say that the outer shape of RCW 85 is more affected by the ultraviolet light and stellar wind from the nearby O-type star than the top of the tallest Pillar of Creation is affected by the ultraviolet light and stellar wind from the cluster NGC 6611. The tallest Pillar lacks the kind of illuminated rim that we see in RCW 85. But clearly, the bombardment of the nearby hot stars is making the Pillars of Creation evaporate.


I'd say that the outer shape of RCW 85 is predominantly shaped by the influence of of the nearby O-type star HD 124314, whereas the outer shape of the tallest Pillar of Creation might also be influenced by the star formation taking place at its top. I think that the star formation of the Pillar of Creation is happening right at the top of the pillar, so that the newborn star's wind is really blowing away the gas around it. Also, I think it is safe to say that the star formation in RCW 85 is taking place deeper down in the gas cloud than the star formation in the Pillar of Creation.

We do see gas being ionized and being made to evaporate from the top of both these "pillars". To me it's not obvious that the embedded star formation in RCW 85 plays much of a part in making gas from its outer rim evaporate.

Ann
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