APOD: In the Arms of NGC 1097 (2022 Nov 16)

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APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by APOD Robot » Wed Nov 16, 2022 5:07 am

Image In the Arms of NGC 1097

Explanation: Spiral galaxy NGC 1097 shines in southern skies, about 45 million light-years away in the heated constellation Fornax. Its blue spiral arms are mottled with pinkish star forming regions in this colorful galaxy portrait. They seem to have wrapped around a small companion galaxy above and right of center, about 40,000 light-years from the spiral's luminous core. That's not NGC 1097's only peculiar feature, though. This very deep exposure hints of faint, mysterious jets, seen to extend well beyond the bluish arms. In fact, four faint jets are ultimately recognized in optical images of NGC 1097. The jets trace an X centered on the galaxy's nucleus, but probably don't originate there. Instead, they could be fossil star streams, trails left over from the capture and disruption of a much smaller galaxy in the large spiral's ancient past. A Seyfert galaxy, NGC 1097's nucleus also harbors a supermassive black hole.

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by Ann » Wed Nov 16, 2022 6:09 am

APOD 16 November 2022 annotated rays.png

At first I thought that the rays emanating from the core of NGC 1097 looked like crepuscular rays, perhaps emanating from holes in a dust structure partly covering, perhaps, a bright but not brilliant accretion disk around the galaxy's central black hole. But on closer inspection, the ray on the far left is bending sharply to the right at top. So that makes it reasonable that the rays are indeed stellar streams, which are remnants of dwarf satellite galaxies of NGC 1097.

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by orin stepanek » Wed Nov 16, 2022 1:45 pm

NGC-1097-LRGB_Ha-rev-12-2022_1024.jpg
What attracted me most was the the kinked Spiral Arm; or Dog
Legged Arm! It does look as tho the small galaxy is in the spiral's arm
at the end of the dog leg! I can make out the "X," just barely! :mrgreen:
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by VictorBorun » Wed Nov 16, 2022 5:24 pm

a pair of jets seem to blow from the centre in the opposite directions. Can they have formed at the tracks of the black hole's jets?

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by VictorBorun » Wed Nov 16, 2022 5:45 pm

orin stepanek wrote: Wed Nov 16, 2022 1:45 pm NGC-1097-LRGB_Ha-rev-12-2022_1024.jpg
What attracted me most was the the kinked Spiral Arm; or Dog
Legged Arm! It does look as tho the small galaxy is in the spiral's arm
at the end of the dog leg! I can make out the "X," just barely! :mrgreen:
Let me try to brighten up the colour of the jets…
No, I can't see the four jets
NGC-1097-LRGB_Ha-rev-12-2022 +.jpg
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by AVAO » Wed Nov 16, 2022 9:29 pm

VictorBorun wrote: Wed Nov 16, 2022 5:24 pm a pair of jets seem to blow from the centre in the opposite directions. Can they have formed at the tracks of the black hole's jets?
I would basically follow your reasoning. The axis runs extremely precisely through the galaxy core. I really don't think this is supposed to be random.

Image


Image
NASA / ESA (SST)

Image
ESO/TIMER survey (MUSE/VLT)

Image
NASA / ESA (HST) jac berne (flickr)
Last edited by AVAO on Thu Nov 17, 2022 8:12 am, edited 1 time in total.

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Wed Nov 16, 2022 10:01 pm

Those faint "pseudo jets" discovered to be composed of stars, not just gas, are indeed remarkable. And the fact that they form an X (the fourth arm is so faint I can't discern it) centered on the galaxy's core is even more remarkable. Now, I can easily imagine trails of stars formed as a result of gravitational interaction with a long gone companion galaxy leaving vast looping streams of stars like the ones seen in the "fossil start streams" link in the text. But what on earth is the mechanism that could account for two almost perfectly linear streams of stars intersecting the core? A central black hole (as others have posited)? Something else?
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by AVAO » Wed Nov 16, 2022 10:18 pm

johnnydeep wrote: Wed Nov 16, 2022 10:01 pm ...the fourth arm is so faint I can't discern it...
Image
https://iopscience.iop.org/article/10.3 ... X/826/1/50

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Wed Nov 16, 2022 10:40 pm

AVAO wrote: Wed Nov 16, 2022 10:18 pm
johnnydeep wrote: Wed Nov 16, 2022 10:01 pm ...the fourth arm is so faint I can't discern it...
Image
https://iopscience.iop.org/article/10.3 ... X/826/1/50
Thanks. I still barely see it, or what I think is it - is it #4 or #5 in my image below? Perhaps the one that extends #1's trail through the nucleus is just wishful thinking on my part.

And that's quite a voluminous explanation of how they formed in that lengthy paper! I'll have to look at it more closely later...

star trail jets in ngc 1097.png
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by AVAO » Thu Nov 17, 2022 11:54 am

johnnydeep wrote: Wed Nov 16, 2022 10:40 pm
AVAO wrote: Wed Nov 16, 2022 10:18 pm
johnnydeep wrote: Wed Nov 16, 2022 10:01 pm ...the fourth arm is so faint I can't discern it...
Image
https://iopscience.iop.org/article/10.3 ... X/826/1/50
Thanks. I still barely see it, or what I think is it - is it #4 or #5 in my image below? Perhaps the one that extends #1's trail through the nucleus is just wishful thinking on my part.

And that's quite a voluminous explanation of how they formed in that lengthy paper! I'll have to look at it more closely later...


star trail jets in ngc 1097.png
If you compare NGC 1097 with NGC 4651, both have different dwarf galaxies in their vicinity. It is plausible that these lose some of their star splendor when penetrating the main galaxy. That would be the most obvious answer. In the case of NGC 4651, however, it almost looks as if the intruder is still coming in the direction of the main galaxy. The "head" of the "comet" could also be a random foreground star (parallax0.5889 ?).

Image
https://www.faintgalaxy.com/ngc4651.html
Image
https://www.cosmotography.com/images/st ... ights.html

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Thu Nov 17, 2022 3:29 pm

AVAO wrote: Thu Nov 17, 2022 11:54 am
johnnydeep wrote: Wed Nov 16, 2022 10:40 pm
Thanks. I still barely see it, or what I think is it - is it #4 or #5 in my image below? Perhaps the one that extends #1's trail through the nucleus is just wishful thinking on my part.

And that's quite a voluminous explanation of how they formed in that lengthy paper! I'll have to look at it more closely later...


star trail jets in ngc 1097.png
If you compare NGC 1097 with NGC 4651, both have different dwarf galaxies in their vicinity. It is plausible that these lose some of their star splendor when penetrating the main galaxy. That would be the most obvious answer. In the case of NGC 4651, however, it almost looks as if the intruder is still coming in the direction of the main galaxy. The "head" of the "comet" could also be a random foreground star (parallax0.5889 ?).

Image
https://www.faintgalaxy.com/ngc4651.html
Image
https://www.cosmotography.com/images/st ... ights.html
So, in the case of NGC 1097, you're thinking a linear trail of stars left by two different companion galaxies perfectly bisecting the nucleus while piercing the main galaxy? But as I write that, the idea of being able to penetrate the nucleus and emerge with enough left over stars to still produce the trail on the other side seems dubious, but at least both trails on the other side seem to contain fewer stars.
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by AVAO » Thu Nov 17, 2022 10:13 pm

johnnydeep wrote: Thu Nov 17, 2022 3:29 pm
AVAO wrote: Thu Nov 17, 2022 11:54 am
johnnydeep wrote: Wed Nov 16, 2022 10:40 pm

Thanks. I still barely see it, or what I think is it - is it #4 or #5 in my image below? Perhaps the one that extends #1's trail through the nucleus is just wishful thinking on my part.

And that's quite a voluminous explanation of how they formed in that lengthy paper! I'll have to look at it more closely later...


star trail jets in ngc 1097.png
If you compare NGC 1097 with NGC 4651, both have different dwarf galaxies in their vicinity. It is plausible that these lose some of their star splendor when penetrating the main galaxy. That would be the most obvious answer. In the case of NGC 4651, however, it almost looks as if the intruder is still coming in the direction of the main galaxy. The "head" of the "comet" could also be a random foreground star (parallax0.5889 ?).

Image
https://www.faintgalaxy.com/ngc4651.html
Image
https://www.cosmotography.com/images/st ... ights.html
So, in the case of NGC 1097, you're thinking a linear trail of stars left by two different companion galaxies perfectly bisecting the nucleus while piercing the main galaxy? But as I write that, the idea of being able to penetrate the nucleus and emerge with enough left over stars to still produce the trail on the other side seems dubious, but at least both trails on the other side seem to contain fewer stars.
Your doubts are justified. I just came across the following article:

"According to James Higdon and John Wallin; “The jets’ radio-X-ray spectral energy distribution is most consistent with starlight. However, from their morphology, optical/near-infrared colors, and lack of H I, we argue that the jets are not tidal tails drawn out of NGC 1097’s disk or stars stripped from the elliptical companion NGC 1097A. We also reject in situ star formation in ancient radio jets as this requires essentially 100% conversion of gas into stars on large scales. Instead, we conclude that the jets represent the captured remains of a disrupted dwarf galaxy that passed through the inner few kiloparsecs of NGC 1097’s disk."
https://www.universetoday.com/61405/ngc ... t-anymore/

Perhaps another explanation could be envisaged. The curved structure around NGC 4651 is very reminiscent of the shell structure of NGC 474. If you look at such a surrounding shell from the side, it becomes linear. If the core rotates, the shell would still be approximately on the axis through the center.
Of course, this hypothesis is doubly vague, since it is still not known which mechanism actually produces these shells...

...also note the shell structure of NGC 1097's small companion galaxy in today's APOD.

Image
NGC474 APOD 2018 February 6

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Sat Nov 19, 2022 7:53 pm

AVAO wrote: Thu Nov 17, 2022 10:13 pm
johnnydeep wrote: Thu Nov 17, 2022 3:29 pm
AVAO wrote: Thu Nov 17, 2022 11:54 am

If you compare NGC 1097 with NGC 4651, both have different dwarf galaxies in their vicinity. It is plausible that these lose some of their star splendor when penetrating the main galaxy. That would be the most obvious answer. In the case of NGC 4651, however, it almost looks as if the intruder is still coming in the direction of the main galaxy. The "head" of the "comet" could also be a random foreground star (parallax0.5889 ?).

Image
https://www.faintgalaxy.com/ngc4651.html
Image
https://www.cosmotography.com/images/st ... ights.html
So, in the case of NGC 1097, you're thinking a linear trail of stars left by two different companion galaxies perfectly bisecting the nucleus while piercing the main galaxy? But as I write that, the idea of being able to penetrate the nucleus and emerge with enough left over stars to still produce the trail on the other side seems dubious, but at least both trails on the other side seem to contain fewer stars.
Your doubts are justified. I just came across the following article:

"According to James Higdon and John Wallin; “The jets’ radio-X-ray spectral energy distribution is most consistent with starlight. However, from their morphology, optical/near-infrared colors, and lack of H I, we argue that the jets are not tidal tails drawn out of NGC 1097’s disk or stars stripped from the elliptical companion NGC 1097A. We also reject in situ star formation in ancient radio jets as this requires essentially 100% conversion of gas into stars on large scales. Instead, we conclude that the jets represent the captured remains of a disrupted dwarf galaxy that passed through the inner few kiloparsecs of NGC 1097’s disk."
https://www.universetoday.com/61405/ngc ... t-anymore/

Perhaps another explanation could be envisaged. The curved structure around NGC 4651 is very reminiscent of the shell structure of NGC 474. If you look at such a surrounding shell from the side, it becomes linear. If the core rotates, the shell would still be approximately on the axis through the center.
Of course, this hypothesis is doubly vague, since it is still not known which mechanism actually produces these shells...

...also note the shell structure of NGC 1097's small companion galaxy in today's APOD.

Image
NGC474 APOD 2018 February 6
Thanks for that article. And from the next paragraph:
We present N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets: A long and narrow “X”-shaped morphology centered near the spiral’s nucleus, right-angle bends, and no discernible dwarf galaxy remnant. A series of jetlike distributions are formed, with the earliest appearing ~1.4 Gyr after impact. Well-defined X shapes form only when the more massive galaxy has a strong disk component. Ram-pressure stripping of the dwarf’s interstellar medium would be expected to occur while passing through NGC 1097’s disk, accounting for the jets’ lack of H I and H II. The remnants’ (B-V) color would still agree with observations even after ~3 Gyr of passive evolution, provided the cannibalized dwarf was low-metallicity and dominated by young stars at impact.”
There's some pretty wild stuff going in NGC 474!
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by Ann » Sun Nov 20, 2022 7:18 am

johnnydeep wrote: Sat Nov 19, 2022 7:53 pm
Thanks for that article. And from the next paragraph:
We present N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets: A long and narrow “X”-shaped morphology centered near the spiral’s nucleus, right-angle bends, and no discernible dwarf galaxy remnant. A series of jetlike distributions are formed, with the earliest appearing ~1.4 Gyr after impact. Well-defined X shapes form only when the more massive galaxy has a strong disk component.

Ram-pressure stripping of the dwarf’s interstellar medium would be expected to occur while passing through NGC 1097’s disk, accounting for the jets’ lack of H I and H II.

The remnants’ (B-V) color would still agree with observations even after ~3 Gyr of passive evolution, provided the cannibalized dwarf was low-metallicity and dominated by young stars at impact.”
This is how ram pressure works:


Galaxies lose gas when they move fast through a medium. The galaxy in the picture above is entering a cluster of galaxies, which is full of million-degree intracluster gas. As ESO 137-001 plunges through this hot intergalactic medium, drawn there by the gravitational pull of the cluster, the hapless captured galaxy is losing its gas. Enormously long filaments of gas are shown in purple in the image, whereas newly formed stars are shown in blue, much closer to the galactic disk. The galaxy itself is losing its gas and its ability to form new stars.

The small galaxy that left the X-formed stellar streams centered on the core of NGC 1097 would have lost its gas and its ability to form new stars as it plunged through the disk of NGC 1097. My own math-idiot guess is that it might have plunged through the disk of NGC 1097 twice.

The Milky Way has star streams, too:

556dfd42c13c1[1].png
Star streams in the Milky Way. Palomar 5 is at lower left. Credit: SDSS/Ana Bonaca.


Palomar 5 star stream is the densest star stream in the Milky Way. Its origin is the globular cluster Palomar 5.


As to why the star streams of NGC 1097 would remain mostly unchanged in color and distinguishable from stars in NGC 1097 and its companion after 3 billion years, this would happen if the shredded galaxy was sufficiently metal-poor and thus different from NGC 1097 and its visible companion.

Let's look at some color-magnitude diagrams of clusters of different ages and metallicities:


M67 is an old metal-rich cluster. Metal-poor clusters evolve slightly differently than metal-rich ones as they age:



Very metal-poor stars go though a "blue phase" during their evolution. They spend some time on the "horizontal branch", where they are much smaller and hotter than they are during their red giant phase. Metal-rich stars do go through a slightly hotter phase during their evolution, too, but in their case, the temperature and color change is so small that it doesn't affect their color very much. They remain cooler, larger and redder than the Sun.


Very metal-poor clusters can stay at the same overall color for billions of years, as their stars move in and out of the red giant branch and the (blue) horizontal branch.


So, to summarize:

A dwarf galaxy may have plunged through the disk of NGC 1097, probably impacting the large galaxy quite close to its center. The dwarf galaxy lost its gas during this crossing and lost its ability to form new stars. The galaxy's existing stars would spread out in long streams. If this small galaxy was metal-poor, its stars would be different and distinguishable from the stars of the visible companion of NGC 1097, which is most likely more metal-rich than the shredded dwarf.

Note that the visible companion lacks gas and dust, too. It, too, may have lost its gas during its interactions with its large bully of a neighbor.

I have looked at other images of the small companion galaxy, NGC 1097A, and haven't found much evidence of it having shells. But we do see at least two shells in the APOD.

APOD 16 November 2022 detail satellite galaxy.png
Possible shell galaxy NGC 1097A.

David Malin explained the shells of NGC 3293 as remnants of the galaxy's history of expanding and contracting, possibly as a consequence of small-scale collisions, which may have left stars behind, similar to how waves lapping on a shore may leave little bits of debris behind.

NGC 1097 has probably rocked the boat of NGC 1097A, too.

Click to play embedded YouTube video.

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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Sun Nov 20, 2022 1:08 pm

All theorizing and "N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets" aside, I still find it very hard to reconcile those linear X-cross jets with a plunging companion galaxy encounter. Just another very surprising thing about the universe I suppose.
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by Chris Peterson » Sun Nov 20, 2022 3:13 pm

johnnydeep wrote: Sun Nov 20, 2022 1:08 pm All theorizing and "N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets" aside, I still find it very hard to reconcile those linear X-cross jets with a plunging companion galaxy encounter. Just another very surprising thing about the universe I suppose.
The science describing such interactions doesn't get much better than N-body simulations.
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Re: APOD: In the Arms of NGC 1097 (2022 Nov 16)

Post by johnnydeep » Sun Nov 20, 2022 10:57 pm

Chris Peterson wrote: Sun Nov 20, 2022 3:13 pm
johnnydeep wrote: Sun Nov 20, 2022 1:08 pm All theorizing and "N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets" aside, I still find it very hard to reconcile those linear X-cross jets with a plunging companion galaxy encounter. Just another very surprising thing about the universe I suppose.
The science describing such interactions doesn't get much better than N-body simulations.
I agree. Still, even seeing with my own eyes just such an N-body simulation in progress that results in the perceived X feature would be very surprising to me! But, or course, I then couldn't rationally deny that it is indeed a possible, or even a likely outcome.
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