APOD: The Bubble and the Star Cluster (2021 Sep 25)

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APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by APOD Robot » Sat Sep 25, 2021 4:05 am

Image The Bubble and the Star Cluster

Explanation: To the eye, this cosmic composition nicely balances the Bubble Nebula at the right with open star cluster M52. The pair would be lopsided on other scales, though. Embedded in a complex of interstellar dust and gas and blown by the winds from a single, massive O-type star, the Bubble Nebula, also known as NGC 7635, is a mere 10 light-years wide. On the other hand, M52 is a rich open cluster of around a thousand stars. The cluster is about 25 light-years across. Seen toward the northern boundary of Cassiopeia, distance estimates for the Bubble Nebula and associated cloud complex are around 11,000 light-years, while star cluster M52 lies nearly 5,000 light-years away. The wide telescopic field of view spans about 1.5 degrees on the sky or three times the apparent size of a full Moon.

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Ann
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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by Ann » Sat Sep 25, 2021 6:13 am

Very nice APOD!!! :D

As you might expect, I have a complaint all the same, and of course it has to do with the color balance of the image and the "orange mysteries" of it. To make you understand what I mean, let's compare today's APOD with an image from Wikimedia.


Please note two things here. The star to the right of the Bubble Nebula is blue in the picture at right, but white in today's APOD. More interestingly, the bright orange star near the upper right edge of M52 that is so prominent in the picture by Lorand Fenyes is invisible in the picture at right, or at least we can't see any trace of orange there!

I'm going to ask you to compare today's APOD with an ESO image of cluster NGC 3293:


Note the prominent orange star in NGC 3293. Doesn't it appear to be much the same color as the bright orange star in cluster M52 in today's APOD?

Actually though, these two orange stars are quite different. The one in M52, SAO 20606, is a star of spectral class F8Ib/II, with a B-V index of +1.02. The orange star in NGC 3293 is a red supergiant of spectral type M1.5Iab-II, with a B-V index of around +1.8 or +1.9. These are very different stars, but the rather deep orange color of SAO 20606 in the APOD makes this F-type giant look like a much cooler M-type supergiant.

There is one other orange peculiarity in today's APOD. Let's look at a closeup of cluster M52.

M52 cluster Lorand Fenyes.png

Note the number of small very orange stars scattered inside M52. What kind of stars are they? We expect only bright giant stars and very faint dwarf stars to be so orange. These orange stars are too faint to be giants and way too bright to be very faint dwarfs.

We must consider the age of M52. According to Wikipedia, its age is 158.5 Myr. Hmm, that's a very precis age! But in any case it means that this cluster is quite young, and more or less comparable in age to the Pleiades. There are no red giants in the Pleiades, and all the bright stars in the cluster of the Seven Sisters are blue B-type stars.

I'd argue that the intensely orange and relatively faint stars that we can see in M52 in today's APOD can't be red giants. We know that more massive (and therefore brighter) stars evolve first, and a blue B-type star that turns into a red (super) giant will certainly not grow fainter as it does so. It will either grow brighter or stay the same.

So here is what I think. Many of the very orange and relatively faint stars seen in M52 in today's APOD are background stars, which would explain their color and faintness. However, these faint orange stars seem more plentiful inside M52 than outside it, so I think that some of them are genuine members of the cluster. Then how do we explain their color and faintness?

We don't. I don't see how we can, if these stars are members of M52. So they must in fact all be background stars, or (most unlikely!!!) M52 must contain two generations of stars. If so, the faint orange stars of M52 would be much older than the blue B-type stars, and they would be normal medium-mass red giants.

Yeah, right!!!!

Ann

P.S. Oh, and yes, I do think that today's APOD "saturates in orange", so that yellowish objects are made to look orange.
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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by orin stepanek » Sat Sep 25, 2021 12:04 pm

Bubble; Banglea and beads!

https://www.youtube.com/watch?v=GXggztdT2XE
241_lorand_fenyes_bubble_m52.jpg
Looks like a giant soap bubble! 8-)
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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by Guest » Sat Sep 25, 2021 2:30 pm

Not following the "lopsided" dimensions cited. The point is that one is closer and smaller, the other larger and farther away, right? So their apparent size is similar. But maybe the distances cited are backwards, or a zero got misplaced?

Shouldn't 10 ly wide at 11,000 ly appear smaller than 25 ly wide at 5,000 ly?

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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by Chris Peterson » Sat Sep 25, 2021 2:42 pm

Guest wrote:
Sat Sep 25, 2021 2:30 pm
Not following the "lopsided" dimensions cited. The point is that one is closer and smaller, the other larger and farther away, right? So their apparent size is similar. But maybe the distances cited are backwards, or a zero got misplaced?

Shouldn't 10 ly wide at 11,000 ly appear smaller than 25 ly wide at 5,000 ly?
For the dimensions and distances given, the Bubble should subtend about 0.05°, or 1/29 of the 1.5° field. The cluster should subtend 0.29°, making it appear about 5.7 times larger than the Bubble, and about 1/5 of the field width. All of which seems pretty consistent with what we're seeing here.
Chris

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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by neufer » Sat Sep 25, 2021 3:19 pm

Chris Peterson wrote:
Sat Sep 25, 2021 2:42 pm
Guest wrote:
Sat Sep 25, 2021 2:30 pm

Not following the "lopsided" dimensions cited. The point is that one is closer and smaller, the other larger and farther away, right? So their apparent size is similar. But maybe the distances cited are backwards, or a zero got misplaced?

Shouldn't 10 ly wide at 11,000 ly appear smaller than 25 ly wide at 5,000 ly?
For the dimensions and distances given, the Bubble should subtend about 0.05°, or 1/29 of the 1.5° field. The cluster should subtend 0.29°, making it appear about 5.7 times larger than the Bubble, and about 1/5 of the field width. All of which seems pretty consistent with what we're seeing here.
The whole "lopsided" explanation is pretty lame, IMO
(; especially, in regard to almost every other "lopsided" astronomical image).

The "Bubble" is indeed around 10 ly wide at ~11,000 ly ...
although the full NGC 7635 is 15′ × 8′ according to Wikipedia.

The closer Star Cluster is around 19 ly wide at ~5,000 ly ..
giving a 13.0′ width according to Wikipedia.

"Lopsided" should have been lopped off the explanation.
https://www.etymonline.com/search?q=lopsided wrote:
lopsided (adj.) also lop-sided, "leaning to one side as a result of being disproportionately balanced," 1711 (lapsided), first used of ships; from lop (v.2) + side (n.).
..................................................
lop (v.2) "droop, hang loosely," as do the ears of certain dogs and rabbits, 1570s, probably a variant of lob or of lap (v.); compare lopsided (1711), which in early use also was lapsided. Lop-eared attested from 1680s.
..................................................
lob (n.) a word of widespread application to lumpish things or suggesting heaviness, pendence, or floppiness, probably ultimately from an unrecorded Old English word. Compare East Frisian lobbe "hanging lump of flesh," Dutch lob "hanging lip, ruffle, hanging sleeve," Danish lobbes "clown, bumpkin."
Last edited by neufer on Sat Sep 25, 2021 5:05 pm, edited 1 time in total.
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Oh, Cleo, you're here too!

Post by neufer » Sat Sep 25, 2021 3:23 pm

Click to play embedded YouTube video.
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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by johnnydeep » Sat Sep 25, 2021 9:55 pm

Chris Peterson wrote:
Sat Sep 25, 2021 2:42 pm
Guest wrote:
Sat Sep 25, 2021 2:30 pm
Not following the "lopsided" dimensions cited. The point is that one is closer and smaller, the other larger and farther away, right? So their apparent size is similar. But maybe the distances cited are backwards, or a zero got misplaced?

Shouldn't 10 ly wide at 11,000 ly appear smaller than 25 ly wide at 5,000 ly?
For the dimensions and distances given, the Bubble should subtend about 0.05°, or 1/29 of the 1.5° field. The cluster should subtend 0.29°, making it appear about 5.7 times larger than the Bubble, and about 1/5 of the field width. All of which seems pretty consistent with what we're seeing here.
I was fooled a bit at first myself, but it helps to know just what the bubble nebula refers to. It's the smaller almost circular "bubble" in the center of the other stuff, and the approximate 5 - 6 times larger apparent size of the 2.5 times larger and half as distant M52 apparent size do look about right. That is, M52 should look about 5.7 times bigger per Chris' calculation:

M52 and the Bubble Nebula Size Comparison.JPG

Though I admit to feeling like I'm being too generous in how far out M52 extends!
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Re: APOD: The Bubble and the Star Cluster (2021 Sep 25)

Post by f.lorand » Sun Sep 26, 2021 9:45 am

Hello!

Your observation is absolutely correct. As I describe on https://fenyeslorand.hu/ngc7635-buborek-m52/ (Hungarian), the picture is a bicolor narrow-band shot, where I'm quoting the RGB color scheme, but not quite accurately (since the image is a sort of splice of RGB and narrow-band photos). I'm primarily interested in the details now, there is indeed some shift in the star colours due to the above. On my other images - where I shoot in RGB colours - this phenomenon does not exist.

So thank you very much for your kind observation, I can absolutely confirm it.

Lorand
https://fenyeslorand.hu/en