APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

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APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by APOD Robot » Thu Jun 11, 2020 4:06 am

Image Barred Spiral Galaxy NGC 1300

Explanation: Big, beautiful, barred spiral galaxy NGC 1300 lies some 70 million light-years away on the banks of the constellation Eridanus. This Hubble Space Telescope composite view of the gorgeous island universe is one of the largest Hubble images ever made of a complete galaxy. NGC 1300 spans over 100,000 light-years and the Hubble image reveals striking details of the galaxy's dominant central bar and majestic spiral arms. In fact, on close inspection the nucleus of this classic barred spiral itself shows a remarkable region of spiral structure about 3,000 light-years across. Like other spiral galaxies, including our own Milky Way, NGC 1300 is thought to have a supermassive central black hole.

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by CuriousChimp » Thu Jun 11, 2020 4:41 am

APOD Robot wrote:
Thu Jun 11, 2020 4:06 am
Like other spiral galaxies, including our own Milky Way, NGC 1300 is thought to have a supermassive central black hole.
Is NGC1300 just too far away for our machinery to resolve the core sufficiently to ascertain the existence of its super-massive singularity or to see the dancing stars around it, as we do with our very own Milky Way? Would a very long exposure image [in the style of Hubble's Deep Field images] work?

Also, am I misinterpreting stuff or is there a string of distant background giant spiral galaxies visible through NGC1300, starting not too far from the right of the Core and sprawling off rightwards? To me, it looks like the string starts with one that seems to glow whitishly then to continue with more reddened spirals. Including the whiter one, I see five of them.

I know it's possible to look through the spiral arms of a galaxy to see others as humans do it all the time, as evidenced by this image, but some of those spirals are seen nearly in line with the Core. Are galaxies really that sparse that we can see through them this well? Or would those blobs be part of 1300? Or is it not possible to tell?

There are some background spirals visible through the edges of the arms at the bottom of the image but I would expect that.

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Ann » Thu Jun 11, 2020 5:31 am

CuriousChimp wrote:
Thu Jun 11, 2020 4:41 am
APOD Robot wrote:
Thu Jun 11, 2020 4:06 am
Like other spiral galaxies, including our own Milky Way, NGC 1300 is thought to have a supermassive central black hole.
Is NGC1300 just too far away for our machinery to resolve the core sufficiently to ascertain the existence of its super-massive singularity or to see the dancing stars around it, as we do with our very own Milky Way? Would a very long exposure image [in the style of Hubble's Deep Field images] work?
Sci-News wrote:

Astronomers use a variety of methods to measure black hole masses.

In giant elliptical galaxies, most measurements come from observations of the orbital motion of stars around the black hole, taken in visible or infrared light.

Another technique, using naturally occurring water masers in gas clouds orbiting around black holes, provides higher precision, but these masers are very rare and are associated almost exclusively with spiral galaxies having smaller black holes.

The ALMA team recently pioneered a new method to study black holes in giant elliptical galaxies.

About 10% of elliptical galaxies contain regularly rotating disks of cold, dense gas at their centers. These disks contain carbon monoxide gas, which can be observed with millimeter-wavelength radio telescopes.

By using the Doppler shift of the emission from molecules of carbon monoxide, astronomers can measure the velocities of orbiting gas clouds, and ALMA makes it possible to resolve the very centers of galaxies where the orbital speeds are highest.






CuriousChimp wrote:
Also, am I misinterpreting stuff or is there a string of distant background giant spiral galaxies visible through NGC1300, starting not too far from the right of the Core and sprawling off rightwards? To me, it looks like the string starts with one that seems to glow whitishly then to continue with more reddened spirals. Including the whiter one, I see five of them.

I know it's possible to look through the spiral arms of a galaxy to see others as humans do it all the time, as evidenced by this image, but some of those spirals are seen nearly in line with the Core. Are galaxies really that sparse that we can see through them this well? Or would those blobs be part of 1300? Or is it not possible to tell?

There are some background spirals visible through the edges of the arms at the bottom of the image but I would expect that.

Yes, there is indeed a string of galaxies to the right of the core of NGC 1300.
















Actually, most of NGC 1300 is really quite flimsy. The picture at right by the Carnegie-Irvine Galaxy Survey gives you a better idea than Hubble image of the relative stellar density of NGC 1300. As you can see, it is really only the tiny inner spiral and the core itself that are bright, with a high stellar density. A portion of the inner arm to the right is somewhat bright, but that's it.

So it is indeed possible to see background galaxies right through most of NGC 1300. What I myself find a bit strange about the Hubble image is that the background galaxies that we see right through the "bulge-bar" of NGC 1300 are so non-red and in some cases even relatively whitish in color. The way I understand it, they should be not only redshift-reddened (because they are so far away), but also dust-reddened, because we see them right through the bulge of NGC 1300. But it is certainly possible that the bulge of NGC 1300 is relatively poor in dust.

Note, though, that the galaxies that we see to the right of the bright arm segment of NGC 1300 at right (at about 3 o'clock) are very much more reddened than the galaxies that are seen through the bulge. The galaxies at right could be farther away, of course, and therefore more redshift-reddened. Nevertheless, the difference is striking.

Admittedly, though, the same color distribution is faintly visible in the Carnegie-Irvine Galaxy Survey image, too.

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Last edited by Ann on Thu Jun 11, 2020 8:41 am, edited 1 time in total.
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by gmPhil » Thu Jun 11, 2020 8:04 am

So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Ann » Thu Jun 11, 2020 8:46 am

gmPhil wrote:
Thu Jun 11, 2020 8:04 am
So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
Well, I think I spotted a June 10 APOD in the morning, around 7 a.m. here in Sweden, which would mean it was in the very wee hours, U.S. time. The APOD was a picture of one of those Kepler planetary systems with many planets. I remember it was a G-type star with eight planets, all of which, unfortunately, are too close to their sun to be habitable as we know it.

Did anyone else spot this APOD?

Ann

EDIT: I think it was this planetary system that was, briefly, the APOD of June 10, 2020.
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Saab story : June 10

Post by neufer » Thu Jun 11, 2020 11:35 am

Ann wrote:
Thu Jun 11, 2020 8:46 am
gmPhil wrote:
Thu Jun 11, 2020 8:04 am

So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
Well, I think I spotted a June 10 APOD in the morning, around 7 a.m. here in Sweden, which would mean it was in the very wee hours, U.S. time. The APOD was a picture of one of those Kepler planetary systems with many planets. I remember it was a G-type star with eight planets, all of which, unfortunately, are too close to their sun to be habitable as we know it.

EDIT: I think it was this planetary system that was, briefly, the APOD of June 10, 2020.
https://en.wikipedia.org/wiki/Saab_Ursaab wrote: <<Ursaab ("original Saab", a.k.a. 92001 & X9248) was the first of four prototype cars made by aeroplane manufacturer Saab AB, which led to production of the first Saab car, the Saab 92 in 1949. Ursaab was driven over 530,000 kilometers, typically in utter secrecy, and usually on narrow and muddy forest roads and in early mornings or late nights. Ursaab was first shown to the press on June 10, 1947 at Saab AB's headquarters. Today it is in the Saab museum in Trollhättan, with a cleaned grille and more roadworthy headlights.>>
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by orin stepanek » Thu Jun 11, 2020 1:16 pm

I don't know anything about NGC1300, but I would imagine t5hey are similar to our own Milky Way!
NGC1300HST1200.jpg
Just beautiful! :wink:
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Re: Saab story : June 10

Post by TheZuke! » Thu Jun 11, 2020 1:37 pm

neufer wrote:
Thu Jun 11, 2020 11:35 am

<<Ursaab ("original Saab", a.k.a. 92001 & X9248) was the first of four prototype cars made by aeroplane manufacturer Saab AB, which led to production of the first Saab car, the Saab 92 in 1949. Ursaab was driven over 530,000 kilometers, typically in utter secrecy, and usually on narrow and muddy forest roads and in early mornings or late nights. Ursaab was first shown to the press on June 10, 1947 at Saab AB's headquarters. Today it is in the Saab museum in Trollhättan, with a cleaned grille and more roadworthy headlights.>>
[/quote]

"Ursaab was driven over 530,000 kilometers, typically in utter secrecy,"

THAT was driven "in utter secrecy"???

:lol2:

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by TheZuke! » Thu Jun 11, 2020 1:42 pm

gmPhil wrote:
Thu Jun 11, 2020 8:04 am
So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
Plausible, or sucked into a Black Hole?

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Sa Ji Tario » Thu Jun 11, 2020 2:52 pm

Large barred galaxy that is close to the limit with Fornax and its cluster, possibly belongs to it but the UIA marked a dividing line that left it in Eridanus.-
In the image it is seen milky and as covered by dense dust but in an enlargement you will see a distant galaxy close to its nucleus, and also in the arms.
At the bottom and sides are several distant galaxies that are probably bound by gravity to the Fornax cluster.

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by owlice » Thu Jun 11, 2020 3:03 pm

gmPhil wrote:
Thu Jun 11, 2020 8:04 am
So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
viewtopic.php?f=9&t=40653#p302974
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by owlice » Thu Jun 11, 2020 3:04 pm

Ann wrote:
Thu Jun 11, 2020 8:46 am
gmPhil wrote:
Thu Jun 11, 2020 8:04 am
So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
Well, I think I spotted a June 10 APOD in the morning, around 7 a.m. here in Sweden, which would mean it was in the very wee hours, U.S. time. The APOD was a picture of one of those Kepler planetary systems with many planets. I remember it was a G-type star with eight planets, all of which, unfortunately, are too close to their sun to be habitable as we know it.

Did anyone else spot this APOD?

Ann
viewtopic.php?f=9&t=40653#p302974
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by orin stepanek » Thu Jun 11, 2020 3:06 pm

Ann wrote:
Thu Jun 11, 2020 8:46 am
gmPhil wrote:
Thu Jun 11, 2020 8:04 am
So.... out of interest, what happened to June 10th? Did the Vogons bulldoze it to make way for a time-tunnel from June 9 straight to June 11?
Well, I think I spotted a June 10 APOD in the morning, around 7 a.m. here in Sweden, which would mean it was in the very wee hours, U.S. time. The APOD was a picture of one of those Kepler planetary systems with many planets. I remember it was a G-type star with eight planets, all of which, unfortunately, are too close to their sun to be habitable as we know it.

Did anyone else spot this APOD?

Ann

EDIT: I think it was this planetary system that was, briefly, the APOD of June 10, 2020.
bystander wrote:
Thu Jun 11, 2020 2:34 pm
viewtopic.php?t=40655
Anyway I couldn't open By's response!

I think what you saw was from Neufer!
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Smile today; tomorrow's another day!

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by heehaw » Thu Jun 11, 2020 3:15 pm

THAT is one LOVELY barred spiral!

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by heehaw » Thu Jun 11, 2020 3:17 pm

Oh I assumed that the missing APOD was because of participation in the strike. I hope it was!

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by bystander » Thu Jun 11, 2020 3:21 pm

orin stepanek wrote:
Thu Jun 11, 2020 3:06 pm
bystander wrote:
Thu Jun 11, 2020 2:34 pm
viewtopic.php?t=40655
Anyway I couldn't open By's response!
owlice wrote:
Thu Jun 11, 2020 3:03 pm
viewtopic.php?f=9&t=40653#p302974
Sorry, this is the link I should have used.
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Avalon » Thu Jun 11, 2020 4:49 pm

So what forces create the bars in such a galaxy? They are such straight, rigid lines in an otherwise curvy, spiral galaxy form.

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by saturno2 » Thu Jun 11, 2020 9:12 pm

beautiful image

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by neufer » Thu Jun 11, 2020 9:48 pm

Avalon wrote:
Thu Jun 11, 2020 4:49 pm

So what forces create the bars in such a galaxy?
They are such straight, rigid lines in an otherwise curvy, spiral galaxy form.
No doubt it is mostly dominated by dark matter... and (like COVID-19)
there is so much we don't understand about dark matter:
  • What is it composed of ?
    What is its distribution ?
    Does it interact with itself (other than gravitationally) ?
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by CuriousChimp » Thu Jun 11, 2020 10:03 pm

Ann wrote:
Thu Jun 11, 2020 5:31 am
Another technique, using naturally occurring water masers in gas clouds orbiting around black holes, provides higher precision, but these masers are very rare and are associated almost exclusively with spiral galaxies having smaller black holes.

The ALMA team recently pioneered a new method to study black holes in giant elliptical galaxies.

About 10% of elliptical galaxies contain regularly rotating disks of cold, dense gas at their centers. These disks contain carbon monoxide gas, which can be observed with millimeter-wavelength radio telescopes.

By using the Doppler shift of the emission from molecules of carbon monoxide, astronomers can measure the velocities of orbiting gas clouds, and ALMA makes it possible to resolve the very centers of galaxies where the orbital speeds are highest.

Cool, thanks.

Yes, there is indeed a string of galaxies to the right of the core of NGC 1300.

Actually, most of NGC 1300 is really quite flimsy. The picture at right by the Carnegie-Irvine Galaxy Survey gives you a better idea than Hubble image of the relative stellar density of NGC 1300. As you can see, it is really only the tiny inner spiral and the core itself that are bright, with a high stellar density. A portion of the inner arm to the right is somewhat bright, but that's it.

So it is indeed possible to see background galaxies right through most of NGC 1300. What I myself find a bit strange about the Hubble image is that the background galaxies that we see right through the "bulge-bar" of NGC 1300 are so non-red and in some cases even relatively whitish in color. The way I understand it, they should be not only redshift-reddened (because they are so far away), but also dust-reddened, because we see them right through the bulge of NGC 1300. But it is certainly possible that the bulge of NGC 1300 is relatively poor in dust.

Note, though, that the galaxies that we see to the right of the bright arm segment of NGC 1300 at right (at about 3 o'clock) are very much more reddened than the galaxies that are seen through the bulge. The galaxies at right could be farther away, of course, and therefore more redshift-reddened. Nevertheless, the difference is striking.

Admittedly, though, the same color distribution is faintly visible in the Carnegie-Irvine Galaxy Survey image, too.

Ann
Thank you. It's nice when I discover really cool stuff like transparent galaxies and strings of distant spirals. This cosmos is just full of gorgeousness and wonders. It's also nice to see that my vision isn't deteriorating as rapidly as I feared it might be.

Could the whitening of the background spirals be due to "special" gases and dusts that selectively absorb red and perhaps infrared? Methane andsuch, like the airs of Neptune and Uranus? That would be cool, too.

Why would Ellipticals have interior discs of gas? Surely that's a trick Spirals are best known for? Could there be a disc-forming bit of physics that is only apparent over smooth, large-scale regions with little mass density such as galaxies? Something magneto-hydro-dynamic or hydrogen-bondy? Some small influence that only shows up when everything else is stable? Or do we have an explanation for Spirals?

heehaw

Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by heehaw » Thu Jun 11, 2020 11:13 pm

Avalon wrote:
Thu Jun 11, 2020 4:49 pm
So what forces create the bars in such a galaxy? They are such straight, rigid lines in an otherwise curvy, spiral galaxy form.
You deserve an answer! The answer is that we ... don't know. That's what I conclude from Wikipedia: https://en.wikipedia.org/wiki/Barred_spiral_galaxy

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by ems57fcva » Fri Jun 12, 2020 1:31 am

Avalon wrote:
Thu Jun 11, 2020 4:49 pm
So what forces create the bars in such a galaxy? They are such straight, rigid lines in an otherwise curvy, spiral galaxy form.
I'll give you my own personal take on that, but with a warning that it is just that: My own personal take.

I believe that strongly barred spiral galaxies such as NGC 1300 are the end stage of a galactic merger. Each of the spiral arms was a separate galaxy which has become tidally stretched out to the point that their former structure is all but lost. The upper arm shows signs of having been a spiral galaxy in its own right with the arms having become side-by-side. The lower arm seems to have been a somewhat smaller elliptical galaxy based on the lack the fine structure visible in the upper arm and apparently less material. The cores of the original galaxies are (were?) located just beyond the ends of the bar, but more on that later.

What I have noticed is that interacting galaxies tend to form a bridge of gas and dust between their cores. This is independent of the tidal tails, and I have seen the secondary tails is some galaxy mergers which go in a different direction from the bridge. A guess is that the bridge forms due to the overlapping dark matter halos increasing the gravitational attraction in those areas. In any case, if the galaxies only interact weakly, the result is a thin bridge that stretches out and breaks. But if the interaction is strong, them a lot of dust and gas goes streaming into the area of lower potential between the galaxies. If enough material gets into that area, it begins to establish a core of its own, and the interacting galaxies may begin to orbit that center. As time goes on, more and more material is drawn out of the original galaxies and into the center. Indeed, the dust lanes leading to the central spiral are evidence that this process is ongoing in NGC 1300.

Now for the weird part: As best I can tell, much of the material that goes into creating the central object for the new galaxy (which is supposedly a black hole) appears to come from the central objects of the merging galaxies (which supposedly were also black holes). As best I have been able to tell, the central objects evaporate due to the new gravitational environment created by the new central object in what was the bridge (but now is the bar), with the liberated material going into the bar and the new central object. I personally do not believe in black holes, but I still find it to be fairly fantastic that an extremely massive gravitationally collapsed object can be made to dissipate. That in one way is just a reflection to the massive amounts of material that are being moved around in such a merger. However, this also is a call for some new physics that goes beyond Einstein's general theory of relativity. So if you wish to take this with more than a grain of salt I will not blame you.

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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Ann » Fri Jun 12, 2020 7:40 am

CuriousChimp wrote:
Thu Jun 11, 2020 10:03 pm

Could the whitening of the background spirals be due to "special" gases and dusts that selectively absorb red and perhaps infrared? Methane andsuch, like the airs of Neptune and Uranus? That would be cool, too.














To my knowledge, foreground dust can never make a background object look whiter. Instead, dust always has a reddening effect. Note how the small dust cloud in the picture at left makes the background stars look progressively redder, until they are blotted out altogether. This means that the dust cloud gets progressively thicker near its center, and the more dust that is present, the stronger is the reddening effect. And of course, the reason why we can't see the center of the Milky Way in optical light is because it is hidden behind our galaxy's thick dark central dust lane.

I included a picture of Uranus and Neptune because they do owe their blue-green or bluish color to the absorption of deep red and infrared wavelengths due to gaseous methane in their atmospheres. But gas is not dust. I found this tidbit of information on the net:
www.classzone.com wrote:
Uranus looks blue-green, and Neptune appears deep blue. The color comes from methane gas, which absorbs certain colors of light. Each planet has methane gas above a layer of white clouds. Sunlight passes through the gas, reflects off the clouds, then passes through the gas again on its way out.
But there is no way that foreground dust will have a whitening effect on a background object. On the other hand, the apparent color of background galaxies are affected both by their own stellar populations (are they dominated by old red or young blue stars?), their amount of dust, and the way their cosmological redshift affects their apparent colors.

Note three galaxies of similar size lining up in a row diagonally (from right to left) under the Tadpole Galaxy's tail. One galaxy is strikingly blue, while the two others are orange in color. My guess is that the blue galaxy is much closer to us than the two orange ones, and that it is also rich in young blue stars. The two other galaxies look really quite orange, and my guess is that they are strongly reddened by their great distance from us. Note however that they also contain dark markings of dust, and it is quite possible that these galaxies contain quite a lot of dust but few young stars. A good example of a dusty galaxy with almost no star formation is NGC 4216, seen here in a picture by Ken Siarkiewicz and Adam Block.

In some cases, very tiny and distant background galaxies look very blue. My take on this is that the light that these galaxies originally emitted, and that now reaches us, was strongly dominated by ultraviolet light from massive star formation. But by the time this ultraviolet light reaches us, it has been reddened to shades of blue. You can find such a group of tiny blue galaxies in the left corner of the Tadpole Galaxy image. But near the right edge of the picture is a group of extremely red galaxies. They obviously contain dust, which is usually a sign of the presence of young blue stars. But they could be dusty galaxies whose young stars are only moderately blue like, say, Sirius, so that their light is reddened into something decidedly non-blue. And the galaxies are obviously quite far away - but not as far away as the little group of blue galaxies in the bottom left corner.


Background galaxies in NGC 1300.png
Now let's look at the background galaxies seen through the bulge of NGC 1300! As you can see, I have labeled them.

I believe that the galaxy that I have called number 1, the whitest of them, is dominated by star formation. I would guess that this is an intrinsically quite blue galaxy. Its distance has reddened the blue color to white. There is probably very little dust in the bulge of NGC 1300 that could add further reddening.

As for number 2, I find it difficult to guess what it is. It looks tilted, which would mean that it is a disk galaxy. It has a bright core, like most large galaxies. But its disk looks altogether yellow. It could be a lenticular galaxy, a disk galaxy without star formation. Admittedly it looks a bit distorted too, so it could be tidally affected by one or more of its neighboring galaxies.

Galaxy number 3 has a tiny yellow core, surrounded by some wispy mostly non-yellow fluff. I'd say that this is a low-mass spiral galaxy with a tiny yellow core and a fluffy bluish disk with some star formation.

Galaxy number 4 looks like an elliptical galaxy to me. There appears to be a tiny yellow companion galaxy tucked up very close to the core of the large elliptical.

Galaxy number 5 looks like s smallish edge-on galaxy with a moderately bright core and a somewhat irregularly shaped disk without star formation. This galaxy could be unrelated to the other four.

It is also possible that galaxies #1 and #3 form a detached pair, while #2 and #4 form another pair.

Of course, I'm just guessing here.

Ann
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Chris Peterson » Fri Jun 12, 2020 1:35 pm

Ann wrote:
Fri Jun 12, 2020 7:40 am
CuriousChimp wrote:
Thu Jun 11, 2020 10:03 pm

Could the whitening of the background spirals be due to "special" gases and dusts that selectively absorb red and perhaps infrared? Methane andsuch, like the airs of Neptune and Uranus? That would be cool, too.
To my knowledge, foreground dust can never make a background object look whiter. Instead, dust always has a reddening effect.
Probably more general to consider that dust in the visible wavelength range (except for material immediately surrounding bright stars) always attenuates the background. Reddening may or may not be apparent. Reddening is a tricky thing in astronomy, because it's not reliably detectable. That's because it's not true reddening (as with redshift) where sources get shifted in wavelength- something that is obvious spectroscopically, but just a change in the balance of a range of wavelengths.
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Re: APOD: Barred Spiral Galaxy NGC 1300 (2020 Jun 11)

Post by Ann » Fri Jun 12, 2020 3:54 pm

CuriousChimp wrote:
Thu Jun 11, 2020 10:03 pm

Why would Ellipticals have interior discs of gas? Surely that's a trick Spirals are best known for? Could there be a disc-forming bit of physics that is only apparent over smooth, large-scale regions with little mass density such as galaxies? Something magneto-hydro-dynamic or hydrogen-bondy? Some small influence that only shows up when everything else is stable? Or do we have an explanation for Spirals?
Not all ellipticals have interior disks of gas, but some do. And not all ellipticals are devoid of gas.
Wikipedia wrote:

Very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies. However, in recent years, evidence has shown that a reasonable proportion (~25%) of early-type (E, ES and S0) galaxies have residual gas reservoirs[21] and low level star-formation.[22]

Herschel Space Observatory researchers have speculated that the central black holes in elliptical galaxies keep the gas from cooling enough for star formation.
Note that up to a fourth of all elliptical and lenticular galaxies are thought to host low-level star formation, which requires the presence of gas. But other ellipticals, those that don't form stars, may still contain gas inside them. But outbursts of the central black hole in these galaxies may keep the gas in these ellipticals too hot and turbulent to form stars.
















And don't forget that an outburst of a black hole absolutely requires something falling into it. That is why galaxies with active nuclei always (as far as I know) contain a rotating accretion disk surrounding the black hole and feeding it, causing its outbursts.

So elliptical galaxies with monstrous central and active black holes are surrounded by rotating accretion disks. And a gas disk surrounding the accretion disk can be thought of as an extension of, and as a feeder of, the accretion disk that feeds the black hole.

Even if the elliptical galaxy does not have an active black hole with an accretion disk, it might still possibly have a gaseous disk surrounding its nucleus.

Or so I think anyway.

























One of the most famous and iconic supernova images shows supernova 1994D in galaxy NGC 4526. Most people who have seen the image at left probably believe that NGC 4526 is a spiral galaxy, but it is not. NGC 4526 is a lenticular galaxy with a small inner disk.

Ann
Color Commentator