APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

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APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by APOD Robot » Mon Sep 25, 2023 4:06 am

Image Arp 142: The Hummingbird Galaxy

Explanation: What's happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown at the bottom, was likely a normal spiral galaxy -- spinning, creating stars -- and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937, just below, and took a turn. Sometimes dubbed the Hummingbird Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. Behind filaments of dark interstellar dust, bright blue stars form the nose of the hummingbird, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like Porpoise or a penguin protecting an egg. The featured re-processed image showing Arp 142 in great detail was taken recently by the Hubble Space Telescope. Arp 142 lies about 300 million light years away toward the constellation of the Water Snake (Hydra). In a billion years or so the two galaxies will likely merge into one larger galaxy.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Mon Sep 25, 2023 4:54 am


The Hummingbird Galaxy? I don't know....


Well, whatever. Arp 142 is one in a million galaxy - or rather, it was the only one of its kind during the cosmologically fleeting moment when it was captured by the Hubble Space Telescope. That perfectly shaped avian head and neck, along with a not-quite-perfect-but-certainly-good-enough beak, is indeed remarkable.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by stacase@hotmail.com » Mon Sep 25, 2023 8:31 am

I probably never noticed before, but how can a Hubble photograph be copyrighted by an amateur astronomer?

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by JohnD » Mon Sep 25, 2023 9:25 am

ARP 142 is "about 300 million LY away" the blurb says. So how close to it is the elliptical, NGC 2937?

I ask, because while the elliptical's stars are just a mist, no individuals discernible, there are many in ARP 142 that appear as single stars. Or do my eyes deceive me?
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by mister T » Mon Sep 25, 2023 10:55 am

A penguin superimposed by it's spirit ancestor a Quetzalcoatalus.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Christian G. » Mon Sep 25, 2023 1:14 pm

"like a penguin protecting an egg" - and getting destroyed by it! Maybe it's just me but sometimes these cute little images don't quite do justice to the cosmic magnitude of such things…

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Mon Sep 25, 2023 1:28 pm

JohnD wrote: Mon Sep 25, 2023 9:25 am ARP 142 is "about 300 million LY away" the blurb says. So how close to it is the elliptical, NGC 2937?

I ask, because while the elliptical's stars are just a mist, no individuals discernible, there are many in ARP 142 that appear as single stars. Or do my eyes deceive me?
John
These?

APOD 25 September 2023 detail annotated.png
Some of the globular clusters in NGC 2937.

They are globular clusters. I have marked eleven of them. Note that they are all more or less the same brightness and the same color (white). A blue dot at 3 o'clock is not a globular cluster, and a red smudge in the outer left part of the elliptical "disk" isn't either (it is probably a background galaxy). Globular clusters are often plentiful around elliptical galaxies.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Chris Peterson » Mon Sep 25, 2023 1:36 pm

stacase@hotmail.com wrote: Mon Sep 25, 2023 8:31 am I probably never noticed before, but how can a Hubble photograph be copyrighted by an amateur astronomer?
Although it's not clear to me that the processor is claiming a copyright, he could (and in some countries there are certain automatic copyrights that occur). But this is not a "Hubble photograph". This is a derivative work created from Hubble data, and while the data itself is freely available to everyone, that does not mean that material produced from it is public domain.
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by JohnD » Mon Sep 25, 2023 1:49 pm

No, Ann! My question must have been unclear may I try again ?
The blurb says that ARP 142 was distorted when "it got too close to the massive elliptical galaxy NGC 2937" which I presume is the one in the centre of your left pic - looks the same as in today's APoD. That galaxy appears as a mist, with no discrete stars, as if it's too far away for even the Hubble to resolve them. But in the same pic, ARP 142 contains many resolved star images.
It would therefore seem that ARP 142 is a lot nearer to us than NGC 2937, which makes me ask if it really is close enough to the other galaxy to be distorted by the other's gravity. Is there another reason for its disruption?

Or, am I misinterpreting the 'stars' in ARP 142? Are they in fact groups of stars, like the clusters you point out around NGC 2937?
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Mon Sep 25, 2023 3:08 pm

JohnD wrote: Mon Sep 25, 2023 1:49 pm No, Ann! My question must have been unclear may I try again ?
The blurb says that ARP 142 was distorted when "it got too close to the massive elliptical galaxy NGC 2937" which I presume is the one in the centre of your left pic - looks the same as in today's APoD. That galaxy appears as a mist, with no discrete stars, as if it's too far away for even the Hubble to resolve them. But in the same pic, ARP 142 contains many resolved star images.
It would therefore seem that ARP 142 is a lot nearer to us than NGC 2937, which makes me ask if it really is close enough to the other galaxy to be distorted by the other's gravity. Is there another reason for its disruption?

Or, am I misinterpreting the 'stars' in ARP 142? Are they in fact groups of stars, like the clusters you point out around NGC 2937?
JOhn
If you ask me, they are massive hot blue stars and therefore bright enough to stand out at Hubble's resolution.

Take a look at a "swathe of stars" in Andromeda:

Blue stars in Andromeda Hubble.png

You can see that groups of blue stars stand out. Do note that there are other parts of Andromeda that contain brighter blue stars than the ones you can see here, but these are the ones that were photographed by Hubble. Not only are these blue stars typically brighter than the other disk stars of Andromeda, but they are also found in groups, in clusters.

There are numerous often non-blue bright-looking stars scattered across the face of Andromeda. Some of them may well be supergiants belonging to Andromeda, but I'd say that most of them are faint foreground Milky Way stars. Do note the globular cluster near the bottom of my attachment.


Very many bright blue stars that look single are in fact multiple, enhancing their brightness. Consider the blue stars of Orion's Belt and Sigma Orionis:

Orions Belt and Sigma Orionis annotated Mike Lynch.png
Orion's Belt and Sigma Orionis. All these bright blue stars are multiple,
except Alnilam, the middle Belt star. Credit: Mike Lynch.


So I'd say that the blue stars that we can see in Arp 142 are massive and bright and in most cases multiple. They are bright enough for Hubble to see. I would guess, however, that what looks like single blue stars in the APOD are not usually entire clusters.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by JohnD » Mon Sep 25, 2023 3:53 pm

Thank you, Ann!
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by orin stepanek » Mon Sep 25, 2023 4:54 pm

Arp142_HubbleChakrabarti_960.jpg
It really does look like a bird!
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by raindcon » Mon Sep 25, 2023 5:39 pm

So the two bright blue stars at the top of the pic are obviously stars from our galaxy but the stream of stars behind the right star looks to be an irregular galaxy. Is that correct? How far distant is that from the star in front?

Thanks.

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by johnnydeep » Mon Sep 25, 2023 7:27 pm

APOD Robot wrote: Mon Sep 25, 2023 4:06 am Image Arp 142: The Hummingbird Galaxy

Explanation: What's happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown at the bottom, was likely a normal spiral galaxy -- spinning, creating stars -- and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937, just below, and took a turn. Sometimes dubbed the Hummingbird Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. Behind filaments of dark interstellar dust, bright blue stars form the nose of the hummingbird, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like Porpoise or a penguin protecting an egg. The featured re-processed image showing Arp 142 in great detail was taken recently by the Hubble Space Telescope. Arp 142 lies about 300 million light years away toward the constellation of the Water Snake (Hydra). In a billion years or so the two galaxies will likely merge into one larger galaxy.
The link-to the instagram post says something that makes no sense to me:
ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.
So, yes, Arp 142 is the interacting galaxy pair consisting of the massive elliptical NGC 2937 below, and the massively distorted spiral NGC 2936 above it. So, what is the "smaller, irregular-shaped galaxy" if not NGC 2936? But the elliptical doesn't look "irregular" at all. And which one is smaller than the other by mass?

Also, is the smudge of stars that deceptively seems to be trailing upward from a foreground star (and looking quite like a comet!) yet another galaxy? If not, what is it?

And trying to summarize Ann's dialog with JohnD above, there are globular clusters visible in the foggy elliptical but no individual stars, whereas there ARE many massive big blue stars visible in the distorted elliptical. Yet both galaxies are much closer to each other than they are to us. Is that the upshot?

arp 142 and components.png
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by alter-ego » Mon Sep 25, 2023 8:57 pm

raindcon wrote: Mon Sep 25, 2023 5:39 pm So the two bright blue stars at the top of the pic are obviously stars from our galaxy but the stream of stars behind the right star looks to be an irregular galaxy. Is that correct? How far distant is that from the star in front?

Thanks.
The galaxy goes by LEDA 1237172, and is identified only as a galaxy without any sub-classification (i.e., not an irregular). The present published distance ≈ 78 ± 6 Mpc from the Milky Way. Note, the distance estimate works for all stars in the MW. FYI, the star you asked about is only 635 pc distant.
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Pastorian » Mon Sep 25, 2023 9:01 pm

raindcon wrote: Mon Sep 25, 2023 5:39 pm So the two bright blue stars at the top of the pic are obviously stars from our galaxy but the stream of stars behind the right star looks to be an irregular galaxy. Is that correct? How far distant is that from the star in front?
johnnydeep wrote: Mon Sep 25, 2023 7:27 pm Also, is the smudge of stars that deceptively seems to be trailing upward from a foreground star (and looking quite like a comet!) yet another galaxy? If not, what is it?
"Above the pair, an unrelated, lone, bluish galaxy, inconsistently cataloged as UGC 5130, appears to be an elongated irregular or an edge-on spiral. Located 230 million light-years away, this galaxy is much closer to us than the colliding pair, and therefore is not interacting with them. It happens to lie along the same line of sight to foreground Milky Way stars caught in the image."
-- https://www.nasa.gov/mission_pages/hubb ... rp142.html

"The interacting pair is catalogued as Arp 142 in Halton Arp’s Atlas of Peculiar Galaxies. Arp 142 is listed as a “galaxy triplet” and includes the blue galaxy appearing next to NGC 2936, catalogued as UGC 5130 or PGC 1237172. PGC 1237172 is either an edge-on spiral or an irregular galaxy. It does not lie at the same distance as the colliding pair and is not physically related to the two galaxies."
https://www.constellation-guide.com/porpoise-galaxy/

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by raindcon » Mon Sep 25, 2023 9:50 pm

Thanks to both 'alter-ego' and 'Pastorian' for the answer to my question. This is truly one of the more interesting pictures that I've seen on APOD. The Hummingbird (or Penguin) Nebula is gorgeous. The variety of galaxies and stars, the types of interactions and their placements within our view just make the whole image very striking.

Thanks again!

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Galaxian » Tue Sep 26, 2023 2:16 am

alter-ego wrote: Mon Sep 25, 2023 8:57 pm
raindcon wrote: Mon Sep 25, 2023 5:39 pm So the two bright blue stars at the top of the pic are obviously stars from our galaxy but the stream of stars behind the right star looks to be an irregular galaxy. Is that correct? How far distant is that from the star in front?

Thanks.
The galaxy goes by LEDA 1237172, and is identified only as a galaxy without any sub-classification (i.e., not an irregular). The present published distance ≈ 78 ± 6 Mpc from the Milky Way. Note, the distance estimate works for all stars in the MW. FYI, the star you asked about is only 635 pc distant.
Cool, thanks.

The star that isn't a "false comet" seems to be sitting "under" something that vaguely looks like a human skull. Is that a part of LEDA 1237172, a blown-away bit of LEDA, something unrelated to LEDA or something that is too small, innocuous and insignificant for us to have named and investigated, yet?

Also, do all of the other galaxies in the image have names and their details recorded somewhere?

Thanks for any information. :)

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Galaxian » Tue Sep 26, 2023 2:18 am

raindcon wrote: Mon Sep 25, 2023 9:50 pm This is truly one of the more interesting pictures that I've seen on APOD. The Hummingbird (or Penguin) Nebula is gorgeous. The variety of galaxies and stars, the types of interactions and their placements within our view just make the whole image very striking.
All true. And I really prefer "Penguin". It seems funnier and warmer for some reason. :)

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by AVAO » Tue Sep 26, 2023 4:25 am

orin stepanek wrote: Mon Sep 25, 2023 4:54 pm Arp142_HubbleChakrabarti_960.jpg
It really does look like a bird!

You're right Orin.

The picture is just difficult to interpret in perspective. In reality it is probably not a hummingbird but an eagle, which from a different perspective looks similar to NGC 6872 (below). In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue. The left front arm begins towards the left as a shortened blue part that rotates and continues in a brown part that stretches from left to right and therefore exactly covers the right "blue" arm behind. This brown part of the left arm is completely in transmitted light but has just as many stars as the illuminated and therefore blue appearing arm behind. However, due to the transmitted light situation, these appear "invisible" to us and we see only the brown dust filaments.

That's why I like this exciting galaxy too.

bigger: https://live.staticflickr.com/65535/529 ... 185d_k.jpg
jac berne (flickr)

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Tue Sep 26, 2023 5:14 am

AVAO wrote: Tue Sep 26, 2023 4:25 am
orin stepanek wrote: Mon Sep 25, 2023 4:54 pm Arp142_HubbleChakrabarti_960.jpg
It really does look like a bird!

You're right Orin.

The picture is just difficult to interpret in perspective. In reality it is probably not a hummingbird but an eagle, which from a different perspective looks similar to NGC 6872 (below). In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue. The left front arm begins towards the left as a shortened blue part that rotates and continues in a brown part that stretches from left to right and therefore exactly covers the right "blue" arm behind. This brown part of the left arm is completely in transmitted light but has just as many stars as the illuminated and therefore blue appearing arm behind. However, due to the transmitted light situation, these appear "invisible" to us and we see only the brown dust filaments.

That's why I like this exciting galaxy too.

bigger: https://live.staticflickr.com/65535/529 ... 185d_k.jpg
jac berne (flickr)
Jac, you wrote:
In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue.
I disagree. The blue parts of NGC 2936 are blue because they are illuminated by hot bright blue stars. You can clearly see the bright blue stars or tiny clusters peppering the blue parts of NGC 2936 and illuminating their vicinity.

The brown parts of NGC 2936 are either dust or low-mass reddish stars.

Blue stars in Arp 142 Hubble.png

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by AVAO » Tue Sep 26, 2023 6:19 pm

Ann wrote: Tue Sep 26, 2023 5:14 am
AVAO wrote: Tue Sep 26, 2023 4:25 am
orin stepanek wrote: Mon Sep 25, 2023 4:54 pm Arp142_HubbleChakrabarti_960.jpg
It really does look like a bird!

You're right Orin.

The picture is just difficult to interpret in perspective. In reality it is probably not a hummingbird but an eagle, which from a different perspective looks similar to NGC 6872 (below). In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue. The left front arm begins towards the left as a shortened blue part that rotates and continues in a brown part that stretches from left to right and therefore exactly covers the right "blue" arm behind. This brown part of the left arm is completely in transmitted light but has just as many stars as the illuminated and therefore blue appearing arm behind. However, due to the transmitted light situation, these appear "invisible" to us and we see only the brown dust filaments.

That's why I like this exciting galaxy too.

bigger: https://live.staticflickr.com/65535/529 ... 185d_k.jpg
jac berne (flickr)
Jac, you wrote:
In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue.
I disagree. The blue parts of NGC 2936 are blue because they are illuminated by hot bright blue stars. You can clearly see the bright blue stars or tiny clusters peppering the blue parts of NGC 2936 and illuminating their vicinity.

The brown parts of NGC 2936 are either dust or low-mass reddish stars.


Blue stars in Arp 142 Hubble.png


Ann
ThanX Ann

OK. Of course, you are certainly right when you say that the blue parts of NGC 2936 are blue primarily because they are illuminated by hot, bright blue stars. This can also be proven very easily by imaging the galaxy in the UV. My statement is therefore wrong in itself, but my point was this: If we assume that the distribution of bright stars in both arms is approximately similar, then there must also be these brighter stars in the front arm. If this is true, it should shine similarly brightly, but it doesn't actually appear that way in the picture. The question arises as to why the front arm is immersed in brown darkness.

But I don't think, that the brown parts of the front arm only contain dust and low-mass reddish stars. There are many examples of backlit parts of galaxies where only dust filaments can be seen and the stars appear as if they have been "switched off". For me, this effect is still unclear. An explanation could be that the dust filaments in the rear part reflect the diffused galactic radiation over all, which does not happen in the front arm, so that the dust filaments appear brown and dark. Is there a better one?

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Tue Sep 26, 2023 8:32 pm

AVAO wrote: Tue Sep 26, 2023 6:19 pm
Ann wrote: Tue Sep 26, 2023 5:14 am
AVAO wrote: Tue Sep 26, 2023 4:25 am


You're right Orin.

The picture is just difficult to interpret in perspective. In reality it is probably not a hummingbird but an eagle, which from a different perspective looks similar to NGC 6872 (below). In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue. The left front arm begins towards the left as a shortened blue part that rotates and continues in a brown part that stretches from left to right and therefore exactly covers the right "blue" arm behind. This brown part of the left arm is completely in transmitted light but has just as many stars as the illuminated and therefore blue appearing arm behind. However, due to the transmitted light situation, these appear "invisible" to us and we see only the brown dust filaments.

That's why I like this exciting galaxy too.

bigger: https://live.staticflickr.com/65535/529 ... 185d_k.jpg
jac berne (flickr)
Jac, you wrote:
In the case of NGC 2936, the right rear arm of the galaxy is illuminated from the nucleus and therefore appears blue.
I disagree. The blue parts of NGC 2936 are blue because they are illuminated by hot bright blue stars. You can clearly see the bright blue stars or tiny clusters peppering the blue parts of NGC 2936 and illuminating their vicinity.

The brown parts of NGC 2936 are either dust or low-mass reddish stars.


Blue stars in Arp 142 Hubble.png


Ann
ThanX Ann

OK. Of course, you are certainly right when you say that the blue parts of NGC 2936 are blue primarily because they are illuminated by hot, bright blue stars. This can also be proven very easily by imaging the galaxy in the UV. My statement is therefore wrong in itself, but my point was this: If we assume that the distribution of bright stars in both arms is approximately similar, then there must also be these brighter stars in the front arm. If this is true, it should shine similarly brightly, but it doesn't actually appear that way in the picture. The question arises as to why the front arm is immersed in brown darkness.

But I don't think, that the brown parts of the front arm only contain dust and low-mass reddish stars. There are many examples of backlit parts of galaxies where only dust filaments can be seen and the stars appear as if they have been "switched off". For me, this effect is still unclear. An explanation could be that the dust filaments in the rear part reflect the diffused galactic radiation over all, which does not happen in the front arm, so that the dust filaments appear brown and dark. Is there a better one?

Jac
Spiral galaxies aren't typically hugely symmetrical, although there are examples of galaxies that are. Like NGC 2857. But even in NGC 2857, there is more star formation in one arm than in the other:


Other galaxies show a huge difference in the amount of star formation in their arms:


So we can't just assume that both arms of a spiral galaxy will contain the same (or more or less the same) amount of star formation.

As for the reddish color of much of NGC 2936, I still believe that these parts owe their color to dust, a myriad of small reddish stars - and, mind you, the sort of processing that made "the red parts" of the galaxy look extra red. I do believe that it would have been possible to process NGC 2936 so that its "red parts" looked less reddish.

However!! I do think that "the intrinsic color" of the non-blue parts of NGC 2936 is indeed redder than the intrinsic color of NGC 2937. The difference, I believe, is due to dust reddening. NGC 2936 contains a lot of dust, and its interaction with NGC 2937 may have scattered quite a bit of that dust across the disk of NGC 2936.

Take a look at nearby NGC 4038 and NGC 4039, the Antennae Galaxies, and note how dust is scattered across the disks of them and reddening their light, particularly their yellow populations.



So, Jac, I have just edited this post, and I took away the suggestion that NGC 2936 would originally have been similar to nearby spiral galaxy M81. M81 has a massive yellow bulge, and the bulge of NGC 2936 really doesn't look remarkably big at all.

One more thing, though. You wrote:

An explanation could be that the dust filaments in the rear part reflect the diffused galactic radiation over all, which does not happen in the front arm, so that the dust filaments appear brown and dark. Is there a better one?
I'm not sure what you mean by that. But bear in m ind that the combined light from galaxies is diffuse and faint. So if you start out with diffuse, faint and scattered light, you are not going to get any sort of bright reflection nebulosity out of that.

There really is dust in the Milky Way that reflects the combined light of our galaxy. The nebulosity it creates is called the Integrated Flux Nebula, or IFN. You can see it in this great picture of Polaris and cluster NGC 188:


But the Integrated Flux Nebula is typically quite faint. I doubt that it would affect the overall appearance of a galaxy.

As to what NGC 2936 originally would have looked like, I don't know. And as to what it would look like if we could see it from another perspective, I frankly have no idea!

Ann
Last edited by Ann on Wed Sep 27, 2023 4:18 am, edited 1 time in total.
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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by ems57fcva » Wed Sep 27, 2023 1:42 am

I don't see any evidence of direct interaction between the Hummingbird galaxy and the (apparently) nearby elliptical galaxy. There is no distortion of the elliptical galaxy nor a bridge of stars connecting the two.

My interpretation is that the Hummingbird Galaxy is itself an ongoing galactic merger, with one component being a startburst galaxy and the other one being one which was composed mostly of gas and dust but limited star formation. This merger is being distorted by the gravitational effects of the nearby elliptical galaxy, making it much more spread out that it otherwise would be. The "eye" is the merged galaxy taking shape, with a bridge of gas running from the frontal arc of gas and dust straight into the Hummingbird's "eye".

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Re: APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

Post by Ann » Wed Sep 27, 2023 3:39 am

johnnydeep wrote: Mon Sep 25, 2023 7:27 pm
APOD Robot wrote: Mon Sep 25, 2023 4:06 am Image Arp 142: The Hummingbird Galaxy

Explanation: What's happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown at the bottom, was likely a normal spiral galaxy -- spinning, creating stars -- and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937, just below, and took a turn. Sometimes dubbed the Hummingbird Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. Behind filaments of dark interstellar dust, bright blue stars form the nose of the hummingbird, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like Porpoise or a penguin protecting an egg. The featured re-processed image showing Arp 142 in great detail was taken recently by the Hubble Space Telescope. Arp 142 lies about 300 million light years away toward the constellation of the Water Snake (Hydra). In a billion years or so the two galaxies will likely merge into one larger galaxy.
The link-to the instagram post says something that makes no sense to me:
ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.
So, yes, Arp 142 is the interacting galaxy pair consisting of the massive elliptical NGC 2937 below, and the massively distorted spiral NGC 2936 above it. So, what is the "smaller, irregular-shaped galaxy" if not NGC 2936? But the elliptical doesn't look "irregular" at all. And which one is smaller than the other by mass?

Also, is the smudge of stars that deceptively seems to be trailing upward from a foreground star (and looking quite like a comet!) yet another galaxy? If not, what is it?

And trying to summarize Ann's dialog with JohnD above, there are globular clusters visible in the foggy elliptical but no individual stars, whereas there ARE many massive big blue stars visible in the distorted elliptical. Yet both galaxies are much closer to each other than they are to us. Is that the upshot?

You got the picture right there, Johnny, because Arp 142 is NGC 2936 and NGC 4237! Arp 142 is the two of them!

(And yes: NGC 2936 and NGC 2937 are very very close to each other, much much closer to each other than they are to us.)

But there is only one elliptical galaxy in this APOD, not two. NGC 2936 is not an elliptical galaxy, but a distorted spiral. Elliptical galaxies are featureless, blob-shaped, dustlane-free, all-yellow bee swarms of stars orbiting a common center of mass. Just like NGC 2937.

The irregular galaxy is the "False Comet" in your picture. These galaxies are typically small, blue, devoid of a bright yellow center and devoid of any sort of regular shape or spiral arms.


I would guess that the irregular galaxy in the APOD is at the same distance as NGC 2936 and NGC 2937, because its stars are resolved to the same extent as the stars of NGC 2936.

However, using Simbad, I found that the designation of "the blue streak" in the APOD is LEDA 1237172. And actually, Simbad told me that LEDA 1237172 is not at the same distance as the two components as Arp 142, because their radial velocity is about 7,000 km/sec, whereas the radial velocity of LEDA 1237172 is "only" some 5,000 km/sec. That is probably a sufficiently significant difference to show that LEDA 1237172 is a foreground object.

Ann
Color Commentator