APOD: Unwinding M51 (2024 Apr 06)

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APOD: Unwinding M51 (2024 Apr 06)

Post by APOD Robot » Sat Apr 06, 2024 4:06 am

Image Unwinding M51

Explanation: The arms of a grand design spiral galaxy 60,000 light-years across are unwound in this digital transformation of the magnificent 2005 Hubble Space Telescope portrait of M51. In fact, M51 is one of the original spiral nebulae, its winding arms described by a mathematical curve known as a logarithmic spiral, a spiral whose separation grows in a geometric way with increasing distance from the center. Applying logarithms to shift the pixel coordinates in the Hubble image relative to the center of M51 maps the galaxy's spiral arms into diagonal straight lines. The transformed image dramatically shows the arms themselves are traced by star formation, lined with pinkish starforming regions and young blue star clusters. Companion galaxy NGC 5195 (top) seems to alter the track of the arm in front of it though, and itself remains relatively unaffected by this unwinding of M51. Also known as the spira mirabilis, logarthimic spirals can be found in nature on all scales. For example, logarithmic spirals can also describe hurricanes, the tracks of subatomic particles in a bubble chamber and, of course, cauliflower.

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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by Ann » Sat Apr 06, 2024 7:41 am

Am I the only one who thinks there is a similarity between today's APOD and yesterday's?


Well, I'm nodding good-bye to yesterday's solar corona to concentrate on today's M51. Being a math idiot, I don't fully understand why the arms of M51 form such perfect lines, but I'll accept that the reason is that the arms are "almost perfectly logarithmic", whatever that means!


Because I can see that the "inner spiral" of M51 seems to follow an amazingly perfect golden ratio shape, whereas the outer arms deviate from this shape, undoubtedly because of the violent forces unleashed by massive star formation.

M51 detail annotated MIRI.png
M51 by MIRI. Credit: ESA/Webb, NASA & CSA,
A. Adamo (Stockholm University) and the FEAST JWST team
APOD Robot wrote:
M51 is one of the original spiral nebulae

One of the original spiral nebulae? M51 obviously isn't a nebula but a galaxy. And why would we call M51 an "original" spiral galaxy? It's no more original than, for example, these distant and very large spiral galaxies. And if it is "one" of the "original" spiral galaxies, which are the others?


What the caption is suggesting (but not really saying) is that M51 was the first spiral galaxy whose spiral arms were discovered! It was "the first spiral galaxy"! Hooray! 🥳 And not only that, but the spiral nature of M51 was probably first discovered (or acknowledged) on April 6, 1845! So in a certain sense of the word, M51 is 179 years old as a spiral galaxy today!!! Hooray, hooray, hooray, hooray!!! 💐🍹 🍰


So it was Lord Rosse who first saw the spiral arms of M51. In 1845, his giant telescope, the 72-inch "Leviathan of Parsonstown", was ready to use.


A truly fascinating tale about the discovery of spiral structure in M51 is told in The M51 mystery: Lord Rosse, Robinson, South and the discovery of spiral structure in 1845. I can't copy any text from this article, because the pages of the original text have been "photographed", so that the entire text is shown as a series of "pictures". You'll understand if you look at the document yourselves.

Anyway. In this article by Wolfgang Steinicke, we are told that Lord Rosse built his huge telescope at the request of his friend, the Reverend Thomas Romney Robinson. The Reverend wanted to use the largest possible telescope to observe nebulas in the sky and prove that they were all just dense clusters of stars! According to Steinicke, there was a current hypothesis at the time that the apparent "nebulae without stars" (such as the Orion Nebula) were in fact gas clouds about to give birth to new stars. But even the milky-looking galaxies that were visible in the sky (such as the Andromeda galaxy) were also thought to be gas clouds about to give birth to new stars.

According to Steinicke, the Reverend Robinson hated this idea of stars in the process of being born, because he believed that God had created all the stars in the heavens once and for all. No new stars could be born, because God had finished his handiwork on the sixth day, or so the Reverend believed. Therefore Robinson wanted to observe both nebulas and galaxies to prove that they were all just dense conglomerates of stars.

So in March of 1845, the Reverend Robinson and another man were observing M51 with Lord Rosse's giant telescope in the hopes of resolving the bright central part of M51 into stars. Lord Rosse himself was not present.

M51 may have looked something like the picture at left when Reverend Robinson observed it. In 1845, it was already known that M51 was surrounded by some sort of ring structure:


So according to Steinicke, Robinson must have seen not only the rings around M51, but he should actually have seen that the "ring" was actually a set of spiral arms. But Steinicke theorizes that Robinson had no interest in either the arms or the rings of M51, because he just wanted to prove that the core of M51 could be resolved into stars.

:arrow:

In other words, Reverend Robinson tried to prove that the core of M51 was actually a globular cluster. He had to observe the "globular cluster nature" of the core of M51 himself to acquire this proof, because there was no way he could take photos of deep-space objects in 1845. And indeed, as he attended his next astronomy meeting, he reported that he had resolved the milky patch of M51 into stars, and he showed the people at the meeting the starry sketch he had made of the galaxy's center.

But, on April 6, 1845, enter Lord Rosse! On that night he observed M51 and noted the spiral nature of it. The Reverend Robinson was not present. In the same month, Lord Rosse made his first sketch of M51:


And the rest, as they say, is history.

Oh, and let's return to the caption of today's APOD, which claimed that M51 was "one of" the original spiral nebulae. Which were the others? Well, two other sort of original (on the heels of M51) "spiral nebulae" were M94 and NGC 2903!


Ann
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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by rstevenson » Sat Apr 06, 2024 11:33 am

I find this mathematical exercise to be quite confusing — not the math, but the intent. What is the purpose of doing this? A spiral galaxy like M51 is quite clear and straightforward to see and understand as a spiral formation. This clever process of turning it into a rectangle adds nothing to that understanding.

Oh well, as Ricky Nelson sang (over 50 years ago!)…
“You see, you can't please everyone
So you got to please yourself”

Rob

Roy

Re: APOD: Unwinding M51 (2024 Apr 06)

Post by Roy » Sat Apr 06, 2024 12:42 pm

rstevenson wrote: Sat Apr 06, 2024 11:33 am I find this mathematical exercise to be quite confusing — not the math, but the intent. What is the purpose of doing this? A spiral galaxy like M51 is quite clear and straightforward to see and understand as a spiral formation. This clever process of turning it into a rectangle adds nothing to that understanding.

Oh well, as Ricky Nelson sang (over 50 years ago!)…
“You see, you can't please everyone
So you got to please yourself”

Rob
To answer Ann's first question - yes, the similarity of the two APODs is evident. And, (pardon the Britishism) What are we meant to learn from these "tricksy pixies"?

Is it just sensationalism? To quote from the same song (Garden Party). "Yoko brought her Walrus, and everyone was there".

'


/

ccdguy

Re: APOD: Unwinding M51 (2024 Apr 06)

Post by ccdguy » Sat Apr 06, 2024 1:20 pm

The Solar image uses clever pixel mapping to clearly show the difference in the Corona's structure , in one image, over its
11 year cycle.

Unwinding M51 unfortunately doesn't bring much new insight to the table...yep, unwind a spiral and you get straight lines....but it
does look cool :ssmile:

Roy

Re: APOD: Unwinding M51 (2024 Apr 06)

Post by Roy » Sat Apr 06, 2024 3:07 pm

Now that i look closer at the unwound image, it DOES show something better that i have always thought unexplained. The spiral arm that passes to NGC5195 is clearly bent towards it, and the fatter spiral arm next down is clearly bent away from it.
Some sort of large scale dynamics at work here.

The Webb telescope image is not broad enough to show this, but does show warm gas and dust better than it shows bright stars.

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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by Christian G. » Sat Apr 06, 2024 3:25 pm

Ann wrote: Sat Apr 06, 2024 7:41 am
A truly fascinating tale about the discovery of spiral structure in M51 is told in The M51 mystery: Lord Rosse, Robinson, South and the discovery of spiral structure in 1845. I can't copy any text from this article, because the pages of the original text have been "photographed", so that the entire text is shown as a series of "pictures". You'll understand if you look at the document yourselves.

Anyway. In this article by Wolfgang Steinicke, we are told that Lord Rosse built his huge telescope at the request of his friend, the Reverend Thomas Romney Robinson. The Reverend wanted to use the largest possible telescope to observe nebulas in the sky and prove that they were all just dense clusters of stars! According to Steinicke, there was a current hypothesis at the time that the apparent "nebulae without stars" (such as the Orion Nebula) were in fact gas clouds about to give birth to new stars. But even the milky-looking galaxies that were visible in the sky (such as the Andromeda galaxy) were also thought to be gas clouds about to give birth to new stars.

According to Steinicke, the Reverend Robinson hated this idea of stars in the process of being born, because he believed that God had created all the stars in the heavens once and for all. No new stars could be born, because God had finished his handiwork on the sixth day, or so the Reverend believed. Therefore Robinson wanted to observe both nebulas and galaxies to prove that they were all just dense conglomerates of stars.

So in March of 1845, the Reverend Robinson and another man were observing M51 with Lord Rosse's giant telescope in the hopes of resolving the bright central part of M51 into stars. Lord Rosse himself was not present.

M51 may have looked something like the picture at left when Reverend Robinson observed it. In 1845, it was already known that M51 was surrounded by some sort of ring structure:


So according to Steinicke, Robinson must have seen not only the rings around M51, but he should actually have seen that the "ring" was actually a set of spiral arms. But Steinicke theorizes that Robinson had no interest in either the arms or the rings of M51, because he just wanted to prove that the core of M51 could be resolved into stars.

:arrow:

In other words, Reverend Robinson tried to prove that the core of M51 was actually a globular cluster. He had to observe the "globular cluster nature" of the core of M51 himself to acquire this proof, because there was no way he could take photos of deep-space objects in 1845. And indeed, as he attended his next astronomy meeting, he reported that he had resolved the milky patch of M51 into stars, and he showed the people at the meeting the starry sketch he had made of the galaxy's center.

But, on April 6, 1845, enter Lord Rosse! On that night he observed M51 and noted the spiral nature of it. The Reverend Robinson was not present. In the same month, Lord Rosse made his first sketch of M51:


And the rest, as they say, is history.

Oh, and let's return to the caption of today's APOD, which claimed that M51 was "one of" the original spiral nebulae. Which were the others? Well, two other sort of original (on the heels of M51) "spiral nebulae" were M94 and NGC 2903!


Ann
Thanks for sharing this fascinating and even amusing tale! I almost like this reverend Robinson:  "Lord Rosse, I want you to build the biggest telescope possible and to find me STARS, alright? No clouds, I want to see STARS"!

SeedsofEarfth

Re: APOD: Unwinding M51 (2024 Apr 06)

Post by SeedsofEarfth » Sat Apr 06, 2024 3:51 pm

As was mentioned by one person here, the spiral arms of such galaxies conform (more or less) to the Fibonacci Sequence, also known as the Golden Mean, a term often used by artists to describe the most pleasing composition in a painting where the main subject is positioned on or near the central region (CORE) of the spiral. The Golden Ratio is approximately 1.618033988749....

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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by De58te » Sat Apr 06, 2024 5:35 pm

I don't see the scientific lesson here about the unwinding. Although you can't see it on the APOD main page, if you click on the larger screen version for it you can see double. The rectangle is divided into two double portions, the left and right sides are with with the identical star formations in each side including not one but two companion galaxies NGC 5195.

There really aren't two NGC 5195s are there?

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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by Ann » Sat Apr 06, 2024 5:46 pm

De58te wrote: Sat Apr 06, 2024 5:35 pm I don't see the scientific lesson here about the unwinding. Although you can't see it on the APOD main page, if you click on the larger screen version for it you can see double. The rectangle is divided into two double portions, the left and right sides are with with the identical star formations in each side including not one but two companion galaxies NGC 5195.

There really aren't two NGC 5195s are there?
Only if you squint.

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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by johnnydeep » Sat Apr 06, 2024 5:52 pm

De58te wrote: Sat Apr 06, 2024 5:35 pm I don't see the scientific lesson here about the unwinding. Although you can't see it on the APOD main page, if you click on the larger screen version for it you can see double. The rectangle is divided into two double portions, the left and right sides are with with the identical star formations in each side including not one but two companion galaxies NGC 5195.

There really aren't two NGC 5195s are there?
That's done so you don't have to map the left side to the right side using your mind alone! 😊 Like unrolling a cylinder over more than one full turn.
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Re: APOD: Unwinding M51 (2024 Apr 06)

Post by johnnydeep » Sat Apr 06, 2024 5:54 pm

Roy wrote: Sat Apr 06, 2024 3:07 pm Now that i look closer at the unwound image, it DOES show something better that i have always thought unexplained. The spiral arm that passes to NGC5195 is clearly bent towards it, and the fatter spiral arm next down is clearly bent away from it.
Some sort of large scale dynamics at work here.

The Webb telescope image is not broad enough to show this, but does show warm gas and dust better than it shows bright stars.

Well, that arm's end is clearly bent away from its "proper" spiral path in the original image too. That's easy to see if you compare it to the opposite arm that's not bent.
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