APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

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APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby APOD Robot » Mon Aug 07, 2017 4:05 am

Image Spiral Galaxy NGC 1512: The Inner Ring

Explanation: Most galaxies don't have any rings -- why does this galaxy have two? To begin, the bright band near NGC 1512's center is a nuclear ring, a ring that surrounds the galaxy center and glows brightly with recently formed stars. Most stars and accompanying gas and dust, however, orbit the galactic center in a ring much further out -- here seen near the image edge. This ring is called, counter-intuitively, the inner ring. If you look closely, you will see this the inner ring connects ends of a diffuse central bar that runs horizontally across the galaxy. These ring structures are thought to be caused by NGC 1512's own asymmetries in a drawn-out process called secular evolution. The gravity of these galaxy asymmetries, including the bar of stars, cause gas and dust to fall from the inner ring to the nuclear ring, enhancing this ring's rate of star formation. Some spiral galaxies also have a third ring -- an outer ring that circles the galaxy even further out.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby bystander » Mon Aug 07, 2017 4:37 am

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby Ann » Mon Aug 07, 2017 6:07 am

A small version of the APOD of July 10, 2017, showing the nuclear ring of NGC 1512.
Well, this is the second time in a few weeks that a picture of NGC 1512 becomes the APOD. The first time was only a few weeks ago, on July 10, which featured the nuclear ring of NGC 1512. The caption of the July 10 APOD described the larger ring being featured in today's APOD as an outer ring, which is made clear in this post by bystander:

APOD Robot wrote: ...
This bar crosses an outer ring, though, a ring not seen as it surrounds the pictured region. Featured in this Hubble Space Telescope image is an inner ring -- one that itself surrounds the nucleus of the spiral. ...

If you follow the link "an outer ring," it becomes very clear.


The nuclear and inner rings of NGC 1097. Photo: ESO/Rob Gendler.







So the ring that was called "an outer ring" in the caption of the July 10 APOD has now been reclassified as an inner ring.

It's a bit confusing.

At right is a picture of NGC 1097, which, as you can see, has both a nuclear ring and an inner ring. But it doesn't have an outer ring, so you feel as if something is missing. Admittedly... if you check out this 860 KB link, you can see a B-R black and white portrait of NGC 1097, where the outer spiral arms overlap, so that they look like a real outer ring.

By the way, do check out this page to see a very nice true-color picture of the inner and outer features of NGC 1512, as well as its small but brightly starforming satellite galaxy, NGC 1510.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby JohnD » Mon Aug 07, 2017 8:27 am

Thank you! This pic dispels better than any explanation my confusion, expressed in the thread linked to by bystander. Did Hoag's object come up then? Is that a nuclear or else an 'inner' ring (astronomers, eh?!) that has lost it's counterpart?

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby starsurfer » Mon Aug 07, 2017 8:48 am

Ann wrote:
A small version of the APOD of July 10, 2017, showing the nuclear ring of NGC 1512.
Well, this is the second time in a few weeks that a picture of NGC 1512 becomes the APOD. The first time was only a few weeks ago, on July 10, which featured the nuclear ring of NGC 1512. The caption of the July 10 APOD described the larger ring being featured in today's APOD as an outer ring, which is made clear in this post by bystander:

Ann

This image of NGC 1512 needs to be featured on APOD a third time! Is definitely a very fascinating galaxy with lots of layers.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby Ann » Mon Aug 07, 2017 8:55 am

JohnD wrote:Thank you! This pic dispels better than any explanation my confusion, expressed in the thread linked to by bystander. Did Hoag's object come up then? Is that a nuclear or else an 'inner' ring (astronomers, eh?!) that has lost it's counterpart?

John


Hoag's Object. NASA and the Hubble Heritage Team/Ray A. Lucas.
Ah, Hoag's Object, that's a weirdo!
Wikipedia wrote:

A nearly perfect ring of young hot blue stars circles the older yellow nucleus of this ring galaxy c. 600 million light-years away in the constellation Serpens.
...
As rare as this type of galaxy is, another more distant ring galaxy (SDSS J151713.93+213516.8)[4] can be seen through Hoag's Object, between the nucleus and the outer ring of the galaxy, at roughly the one o'clock position in the image shown here.
...
In the initial announcement of his discovery, Hoag proposed the hypothesis that the visible ring was a product of gravitational lensing. This idea was later discarded because the nucleus and the ring have the same redshift, and because more advanced telescopes revealed the knotty structure of the ring, something that would not be visible if the ring were the product of gravitational lensing.
...
So-called "classic" ring galaxies are generally formed by the collision of a small galaxy with a larger disk-shaped galaxy. This collision produces a density wave in the disk that leads to a characteristic ring-like appearance.
...
However, there is no sign of any second galaxy that would have acted as the "bullet", and the likely older core of Hoag's Object has a very low velocity relative to the ring, making the typical formation hypothesis quite unlikely.
...
Interestingly, a few galaxies share the primary characteristics of Hoag's Object, including a bright detached ring of stars, but their centers are elongated or barred, and they may exhibit some spiral structure. While none match Hoag's Object in symmetry, this handful of galaxies are known to some as Hoag-type galaxies.
...
Noah Brosch and colleagues showed that the luminous ring lies at the inner edge of a much larger neutral hydrogen ring.


So maybe the visible blue ring of Hoag's Object might be called an "inner ring" after all, since there is a larger ring of neutral hydrogen outside it!

But this is all I know about Hoag's Object, sorry.

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This is not a spiral.

Postby neufer » Mon Aug 07, 2017 11:46 am

Art Neuendorffer

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby Ann » Mon Aug 07, 2017 4:25 pm

Click to play embedded YouTube video.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby ems57fcva » Mon Aug 07, 2017 4:40 pm

ImageFWIW - I see in NGC 1512 the tail end of a galactic merger. The Inner Ring (whose context can be seen in the accompanying GALEX image) is just two spiral arms that start from the ends of the bar. That they overlap and become more diffuse afterwards does not change their state. In fact, the overlap may be what makes the Inner Ring so prominent. And the disruption caused by NGC 1510 (to the right and slightly below the center of NGC 1512) may be part of what make NGC 1512 so weird,

My belief is that spiral arms like there are the tidally distorted remains of two galaxies that captured each other and merged. The bar started as a bridge between the cores of the galaxies, pulling material in from both. When the galaxies interact strongly enough, this bridge starts to dominate things and begins forming a core of its own. That somehow draws the cores out of the other two galaxies and into this new core. the nuclear ring is like a galactic accretion disk for material flowing from the outer regions and into this new core.

I have not figured out what happens to the central objects in the galaxies (which as supposedly black holes). One possibility is that they get pulled down the bridge/bar and into the new core, where they merge. Another is that was material is drawn out of the central areas of the original galaxies, the old central objects dissipate and their material gets incorporated into the new central object forming in the center of the bar. However, this scenario implies that the central objects are not black holes and can dissipate as pressure is removed from them. I'm OK with that since I do not believe in black holes, but that is another matter.

For now, all that I can say is that I have seen various pictures of merging galaxies that lead me to be comfortable with merging galaxies becoming a barred spiral that then over time relaxes into a normal spiral. However, I have yet to see a picture that says to me that here are the central objects moving down the bridge/bar. Instead all that I ever see are streams of gas going down the bar to the center. So I suspect that the central objects dissipate instead of move, but cannot even begin to prove that at this time.

Self-assessment: A neat idea. But extraordinary claims require extraordinary evidence. And I do not have that ... yet.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby danhammang » Mon Aug 07, 2017 4:46 pm

I usually check in to thank the photographer/image processor for the work they've done and for their generosity. Today, though, is a stratight up selection and explanation by Drs. Nemiroff and Bonnell that evokes, for me the wonder of our universe and the technology that allows me to see it here at home during my morning chat with my wife, sitting on the couch with a cup of coffee. You both give time amidst your busy schedules to bring this to us. I come just about every day and you regularly deliver images that delight. Thank you, a deep thank you for all your efforts, for sharing what is clearly your own sense of wonder.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby chuckster » Mon Aug 07, 2017 7:13 pm

danhammang wrote:I usually check in to thank the photographer/image processor for the work they've done and for their generosity. Today, though, is a stratight up selection and explanation by Drs. Nemiroff and Bonnell that evokes, for me the wonder of our universe and the technology that allows me to see it here at home during my morning chat with my wife, sitting on the couch with a cup of coffee. You both give time amidst your busy schedules to bring this to us. I come just about every day and you regularly deliver images that delight. Thank you, a deep thank you for all your efforts, for sharing what is clearly your own sense of wonder.



Well said, danhammang, and DITTO. If 'privilege' can be said to be an emotion that you feel, I nominate 'perspective' to be added to the same class of emotional cocktail. As an ex-climber, I calibrated myself before the majesty and immensity of the Sierra Nevada. Being a speck, a moment of light fading in the grass, is OK. Up in the mtns, and millions of light years out in space, I got to see these things, and listened to the geologists and astronomers tell me about them.

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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby MargaritaMc » Mon Aug 07, 2017 8:38 pm

I don't think this has been posted. It's recent ESA Hubble photo release with what I found to be interesting info about NGC 1512 and its dwarf neighbour NGC 1510
http://spacetelescope.org/news/heic1712/
heic1712 — Photo Release
Galactic David and Goliath
27 July 2017
The gravitational dance between two galaxies in our local neighbourhood has led to intriguing visual features in both as witnessed in this new NASA/ESA Hubble Space Telescope image. The tiny NGC 1510 and its colossal neighbour NGC 1512 are at the beginning of a lengthy merger, a crucial process in galaxy evolution. Despite its diminutive size, NGC 1510 has had a significant effect on NGC 1512’s structure and amount of star formation.
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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby Ann » Mon Aug 07, 2017 11:59 pm

ems57fcva wrote:ImageFWIW - I see in NGC 1512 the tail end of a galactic merger. The Inner Ring (whose context can be seen in the accompanying GALEX image) is just two spiral arms that start from the ends of the bar.


Indeed, many galactic rings are really overlapping spiral arms.

My belief is that spiral arms like there are the tidally distorted remains of two galaxies that captured each other and merged.


I don't think so. We see no sign that the well-ordered inner parts of NGC 1512 have been affected by a merger. On the other hand, the outer, extremely faint and very disordered outer spiral arms of NGC 1512 are clearly affected by the tidal effects of the galaxy's interactions with NGC 1510.

The bar started as a bridge between the cores of the galaxies, pulling material in from both. When the galaxies interact strongly enough, this bridge starts to dominate things and begins forming a core of its own. That somehow draws the cores out of the other two galaxies and into this new core. the nuclear ring is like a galactic accretion disk for material flowing from the outer regions and into this new core.


I don't think that there are any observations that support this hypothesis.

For now, all that I can say is that I have seen various pictures of merging galaxies that lead me to be comfortable with merging galaxies becoming a barred spiral that then over time relaxes into a normal spiral.


Barred spirals are more common in the nearby universe than they were in the past, in the very distant universe. So there are no signs that barred galaxies typically lose their bars and become nonbarred over time.

NASA wrote:

In a landmark study of more than 2,000 spiral galaxies from the largest galaxy census conducted by NASA's Hubble Space Telescope, astronomers found that so-called barred spiral galaxies were far less plentiful 7 billion years ago than they are today, in the local universe.


ems57fcva wrote:However, I have yet to see a picture that says to me that here are the central objects moving down the bridge/bar. Instead all that I ever see are streams of gas going down the bar to the center. So I suspect that the central objects dissipate instead of move, but cannot even begin to prove that at this time.

Self-assessment: A neat idea. But extraordinary claims require extraordinary evidence. And I do not have that ... yet.


Good! I like your interest in space, your interest in galaxies, your willingness to speculate, and your self-reflection and humility. :D

As for myself, I don't know where galactic bars come from, and I'm not too willing to speculate. I suspect that they form naturally as stellar orbits and gas movements in galaxies interact, set up feedback and create self-regulating periods. But I'll leave it to the mathematicians here to say if I am even a little bit right or just plain mistaken.

A few more points here.

Isolated, non-interacting galaxies, barred and unbarred.
Source: https://ned.ipac.caltech.edu/level5/Sep ... uta15.html
Caltech.edu wrote:

Durbala et al. (2008) analyzed the photometric properties of 100 isolated Sb-Sc AMIGA galaxies, and found that a majority have pseudobulges rather than classical bulges. In comparing the properties of isolated galaxies with a sample of Sb-Sc galaxies selected without an isolation criterion, Durbala et al. found that isolated spirals have longer bars and, using CAS parameters, also less asymmetry, central concentration, and clumpiness,


Super-sized spirals with double nuclei.
Photo: Sloan Digital Sky Survey.







But as for mergers, there really is a very rare class of super-sized spiral galaxies that just possibly may owe their humongous size to a galactic mergers.

Americaspace.com wrote:
By far, some of the most massive and luminous galaxies known to date are ellipticals.
...
Ogle and colleagues expected to only find similar supergiants like M87 in a sample of nearly 800,000 galaxies that they extracted from the NED database for their research.

Yet, to their surprise, their search revealed a total of 53 spiral galaxies with sizes and luminosities that by far exceeded that of spirals like our own. Dubbed ‘super spirals’ by the researchers, these newly found behemoths which lie between 1.2 and 3.5 billion light-years away, were found to be eight and fourteen times brighter than the Milky Way while also exhibiting a star formation rate that was up to 30 times higher.
...
One of the things that stands out regarding these newly found super spiral galaxies, is the strange fact that four of them appear to have two galactic nuclei, making them look like two egg yolks in a frying pan, similar to what has also been observed in recent years in a handful of much smaller spirals. Could this be evidence of an ongoing galaxy merger?
...
“Super spirals display a range of morphologies, from flocculent to grand-design spiral patterns”, write the researchers in their study which was published at The Astrophysical Journal. “At least 9 super spirals have prominent stellar bars visible in the SDSS images.
...
Whatever the case may be, the finding of just 53 such galaxies out of a total of 800,000 suggests that super spirals are extremely rare specimens in the wider population of the galactic zoo.


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Re: APOD: Spiral Galaxy NGC 1512: The Inner Ring (2017 Aug 07)

Postby ems57fcva » Tue Aug 08, 2017 3:10 am

Ann wrote:
ems57fcva wrote:My belief is that spiral arms like there are the tidally distorted remains of two galaxies that captured each other and merged.


I don't think so. We see no sign that the well-ordered inner parts of NGC 1512 have been affected by a merger. On the other hand, the outer, extremely faint and very disordered outer spiral arms of NGC 1512 are clearly affected by the tidal effects of the galaxy's interactions with NGC 1510.


I find this response to be a little disingenuous. I am saying that the "Inner Ring" and bar are a result to two galaxies merging to create NGC 1512. NGC 1510, which affecting things as stated, was not a part of that merger. So to me, the entire set-up speaks of a merger. However, I will also admit that this is not the standard interpretation of a picture like this.

The bar started as a bridge between the cores of the galaxies, pulling material in from both. When the galaxies interact strongly enough, this bridge starts to dominate things and begins forming a core of its own. That somehow draws the cores out of the other two galaxies and into this new core. the nuclear ring is like a galactic accretion disk for material flowing from the outer regions and into this new core.


I don't think that there are any observations that support this hypothesis.


You can put together a sequence of pictures starting with galaxies that are just approaching to having a small bar between them to having a big (and getting fat) bar between them to a barred spiral. If you look of it, you will end up with a fairly good progression in that way.

But I will not blame you for not taking my word for it. I need to take the time to put together a sequence like that to make my point.

For now, all that I can say is that I have seen various pictures of merging galaxies that lead me to be comfortable with merging galaxies becoming a barred spiral that then over time relaxes into a normal spiral.


Barred spirals are more common in the nearby universe than they were in the past, in the very distant universe. So there are no signs that barred galaxies typically lose their bars and become nonbarred over time.


I think that we can agree to disagree on this one. However, I do admit that mine is the non-standard.

However, I have yet to see a picture that says to me that here are the central objects moving down the bridge/bar. Instead all that I ever see are streams of gas going down the bar to the center. So I suspect that the central objects dissipate instead of move, but cannot even begin to prove that at this time.

Self-assessment: A neat idea. But extraordinary claims require extraordinary evidence. And I do not have that ... yet.


Good! I like your interest in space, your interest in galaxies, your willingness to speculate, and your self-reflection and humility. :D

As for myself, I don't know where galactic bars come from, and I'm not too willing to speculate. I suspect that they form naturally as stellar orbits and gas movements in galaxies interact, set up feedback and create self-regulating periods. But I'll leave it to the mathematicians here to say if I am even a little bit right or just plain mistaken.


... And I do not mind speculating.

BTW - As I look more, I have notice that the ends of the bars get brighter again. I take those brighter areas to be the remains of the original galactic cores. And there is a lot of gas and dust heading towards the center, and I assume that the dark matter is also doing the same (and may even be driving this business). But what is happening to those cores? And what has become (or is becoming) of their central objects? I have my speculations, but I know that observation is key, and I too want to know what the reality is.


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