APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

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APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by APOD Robot » Tue Jan 23, 2018 5:09 am

Image Ribbons and Pearls of Spiral Galaxy NGC 1398

Explanation: Why do some spiral galaxies have a ring around the center? Spiral galaxy NGC 1398 not only has a ring of pearly stars, gas and dust around its center, but a bar of stars and gas across its center, and spiral arms that appear like ribbons farther out. The featured image was taken with ESO's Very Large Telescope at the Paranal Observatory in Chile and resolves this grand spiral in impressive detail. NGC 1398 lies about 65 million light years distant, meaning the light we see today left this galaxy when dinosaurs were disappearing from the Earth. The photogenic galaxy is visible with a small telescope toward the constellation of the Furnace (Fornax). The ring near the center is likely an expanding density wave of star formation, caused either by a gravitational encounter with another galaxy, or by the galaxy's own gravitational asymmetries.

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Boomer12k » Tue Jan 23, 2018 11:26 am

"What is the sound of a Galactic Density Wave?" --- Future Buddhist Scientific Koan...(In reference to the article on it)...

"How many times have you read the Density Wave Sutra?"....the Master asks...

"I...I...came...to lean Astronomy, Master....", Says the Student....

"Out, return when you have full knowledge..." The Master intoned...

From the future space Kung Fu thriller..."The 36th Galaxy of Shaolin"....

This is a parody of a kung fu movie...

Awesome image...great detail...
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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by NCTom » Tue Jan 23, 2018 1:13 pm

Absolutely gorgeous photo! Trying to imagine the dynamics that created this wonder makes it even more awesome.

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Fred the Cat » Tue Jan 23, 2018 2:18 pm

If you’ve ever blown a smoke ring, the smoke “rolls” through space. It makes you wonder if a collision could cause a roiling of stars. :?:
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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Ann » Tue Jan 23, 2018 2:57 pm

NGC 1398 is a hauntingly beautiful galaxy. Its overall color is very non-blue, which is to be expected, since a near-perfect galactic symmetry requires very limited amounts of star formation. The B-V of NGC 1398 is 0.900 and its U-B is 0.430.

I'm reminded of William Blake's poem The Tyger (another non-blue entity):

Tyger Tyger, burning bright,
In the forests of the night;.
What immortal hand or eye,.
Could frame thy fearful symmetry?

Not that I think that a hand or an eye shaped the "fearful" symmetry of NGC 1398. But that is another matter.

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by heehaw » Tue Jan 23, 2018 3:47 pm

Makes me dizzy to look at it!

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Spin Dizzy » Tue Jan 23, 2018 5:07 pm

heehaw wrote:Makes me dizzy to look at it!
I've seen galaxies depicted in videos spinning both ways but, do galaxies generally spin with the spiral arms leading or trailing the galactic core? Or is there no one typical way?

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Chris Peterson » Tue Jan 23, 2018 5:16 pm

Spin Dizzy wrote:I've seen galaxies depicted in videos spinning both ways but, do galaxies generally spin with the spiral arms leading or trailing the galactic core? Or is there no one typical way?
There is a "typical" way. The vast majority of spiral galaxies are spinning such that their spiral arms appear to be trailing. But this is not universally true. There are a few examples of spiral galaxies where the arms are leading. The mechanisms behind spiral structure are not well understood in general, so there is no clear explanation of the patterns we see. The very small number of "reverse" spinning galaxies might be a consequence of earlier galactic collisions, but that's only one idea.
Chris

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by heehaw » Tue Jan 23, 2018 5:48 pm

Chris Peterson wrote:
Spin Dizzy wrote:I've seen galaxies depicted in videos spinning both ways but, do galaxies generally spin with the spiral arms leading or trailing the galactic core? Or is there no one typical way?
There is a "typical" way. The vast majority of spiral galaxies are spinning such that their spiral arms appear to be trailing. But this is not universally true. There are a few examples of spiral galaxies where the arms are leading. The mechanisms behind spiral structure are not well understood in general, so there is no clear explanation of the patterns we see. The very small number of "reverse" spinning galaxies might be a consequence of earlier galactic collisions, but that's only one idea.
Interested to learn that "reverse" business from Chris! I do vividly remember a Space Telescope "sales talk" to the NASA administrator (HST had just been omitted by OMB) by the community, and Phil Morrison asking us all (and the NASA Administrator) to "visualize a galaxy." When we had done so, he said "you all got it wrong! You did not take the TIME element into account: visualize the galaxy as ROTATING as you watch." Well, a few minutes later he said "you all got it all wrong AGAIN! You forgot that a supernova goes off every few hundred years, but galaxies rotate once in maybe 250 million years,\: so as you visualize, your galaxy should look like a fireworks-pinwheel, with supernovae, galore, all the time!"

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by BDanielMayfield » Tue Jan 23, 2018 8:29 pm

I certainly accept the general belief that galactic collisions are behind much of the structure that they display. However, in this case, NGC 1398 looks too, well, "perfect". (This was the word my wife used to describe it when I showed it to her, and I had had the same thought myself.) Is this galaxy in a crowded neighborhood with frequent (universally speaking) mergers? My naive guess would be that NGC 1398 is a loner that has developed its stately form in a relatively isolated area.

Anyone have a wider view of the vicinity NGC 1398 is in?
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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by MarkBour » Tue Jan 23, 2018 9:27 pm

That is one gorgeous image, especially at the higher resolution.

Thanks to my tutelage in this forum, I have a new appreciation for the dust lanes in this image. Whereas I used to envision them quite differently, I now see them as material that has come from the stars. Where there is high density of stars, this dust gets blown away above and below the galactic disk. (Somewhat like smoke from a fire.) This image would go along with that thought. The dust lanes appear to coincide with the areas of rich star formation, i.e. the spirals.

Incidentally, it looks to me as though NGC 1398 has basically two spiral arms. Would other readers agree with that? Would these be considered tightly wound? If so, I note that one of the arms is far thicker and more "feathered" than the other. The APOD caption suggests that the inner ring is perhaps expanding outward. I wonder how it will change over a very long time.
Capture.jpg
A final question for today. In this image, the spirals appear to have both pink and blue granules in them (close-up at right).

At a distance of 65 M Ly, I wonder what we are able to see that appears this way. Is every one a cluster, or can they be lesser collections of star population, but perhaps still regions of higher-than-average stellar density?
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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Ann » Wed Jan 24, 2018 2:31 am

MarkBour wrote:That is one gorgeous image, especially at the higher resolution.

Thanks to my tutelage in this forum, I have a new appreciation for the dust lanes in this image. Whereas I used to envision them quite differently, I now see them as material that has come from the stars. Where there is high density of stars, this dust gets blown away above and below the galactic disk. (Somewhat like smoke from a fire.) This image would go along with that thought. The dust lanes appear to coincide with the areas of rich star formation, i.e. the spirals.

Incidentally, it looks to me as though NGC 1398 has basically two spiral arms. Would other readers agree with that?
I agree that it looks as if NGC 1398 has two prominent inner arms (and now I'm not talking about the inner ring). The inner arms are relatively long and thin. ON the right-hand side of the image, we can see what looks like three arms winding around the main body of the galaxy. But on the left-hand side, the arms appear to break up into numerous little "arm-lets".
Would these be considered tightly wound?


Absolutely! The arms are tightly wound. NGC 1398 is classified as Hubble class SBab, or so I think. That means that the galaxy is a spiral with a bar, a large bulge and tightly wound arms. The galaxies with loose arms are classified as Hubble class Sc or even Sd.
If so, I note that one of the arms is far thicker and more "feathered" than the other. The APOD caption suggests that the inner ring is perhaps expanding outward. I wonder how it will change over a very long time.
Well, one possibility is that, in the very long run, NGC 1398 will run out of gas completely, and all star formation will stop. The dust will spread out too and become invisible. So in the very long run, NGC 1398 may look like NGC 936, here photographed by SDSS SkyServer.
Capture.jpg
A final question for today. In this image, the spirals appear to have both pink and blue granules in them (close-up at right).

At a distance of 65 M Ly, I wonder what we are able to see that appears this way. Is every one a cluster, or can they be lesser collections of star population, but perhaps still regions of higher-than-average stellar density?
The filters used for this image are blue, green, red and H-alpha. The H-alpha filter makes the emission nebulas stand out strongly. So we have every reason to believe that the pink splotches represent pink emission nebulas like, for example, the Orion Nebula.

The blue blobs are young star clusters.

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Chris Peterson » Wed Jan 24, 2018 5:41 am

BDanielMayfield wrote:I certainly accept the general belief that galactic collisions are behind much of the structure that they display.
I think the general view is that spiral galaxies are as they are because they haven't undergone any large collisions. Galactic collisions seem to turn spirals (which are unperturbed) into elliptical and irregular galaxies.
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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by BDanielMayfield » Wed Jan 24, 2018 1:27 pm

Chris Peterson wrote:
BDanielMayfield wrote:I certainly accept the general belief that galactic collisions are behind much of the structure that they display.
I think the general view is that spiral galaxies are as they are because they haven't undergone any large collisions. Galactic collisions seem to turn spirals (which are unperturbed) into elliptical and irregular galaxies.
In hindsight that was a poorly thought out statement, which needed to be corrected. :oops:

At least I learned something important in this thread about spiral galaxies. Also, the guess I made about NGC 1398 being an isolated galaxy was correct, which I would have learned if I had just read the first hyperlink in the Explanation.

Are Barred Spirals more common than spirals lacking bars?

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by Ann » Wed Jan 24, 2018 2:53 pm

BDanielMayfield wrote:

Are Barred Spirals more common than spirals lacking bars?

Bruce
I can't say, but at least they are more common in the nearby Universe than in the distant one. So they are becoming more and more common.

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Re: APOD: Ribbons and Pearls of Spiral Galaxy... (2018 Jan 23)

Post by MarkBour » Wed Jan 24, 2018 11:05 pm

Ann wrote:
BDanielMayfield wrote:
Are Barred Spirals more common than spirals lacking bars?
Bruce
I can't say, but at least they are more common in the nearby Universe than in the distant one. So they are becoming more and more common.
Ann
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