APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

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Expand view Topic review: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by geckzilla » Sun Jan 17, 2016 11:05 am

Yeah, it's hard, and not everyone is going to get it, but it doesn't mean that the person who tried to describe a lingonberry to someone who's never tried one lied while doing it.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Sun Jan 17, 2016 10:30 am

geckzilla wrote:I've said it before and I'll say it again, the colors are no more a lie than one language translated to another language.
Translation is a hard thing.
Image












At left you can see lingonberries, which are, or so I believe, relatively unknown in the countries in the world where very many people speak English as their first language. In Sweden, lingonberries are used to make lingonberry jam, which is eaten with many "typically Swedish" dishes, like meatballs and mashed potatoes. Anyone who lives near an IKEA department store anywhere in the world can go to their restaurant and sample their meatballs with potatoes and lingonberry jam, but for those who don't have an IKEA store nearby, the word "lingonberries" probably won't ring a bell. You could translate it by calling them cranberries, but it wouldn't be the same thing.

What I'm trying to say is that I have the greatest respect for those who try to "translate" information about other parts of the electromagnetic spectrum than the optical one into images that we can see. It's such a great thing that different telescopes have given us images of space in the X-ray, ultraviolet, infrared and radio part of the spectrum. We have learned such a tremendous amount about the universe that would have been unknown to us if we had been forced to rely on the information that is available to the rods and cones in our eyes.

Therefore it is necessary, or at least very desirable, to "translate" information about other parts of the electromagnetic spectrum into optical colors and present it as hues that we can see.

But in the end something is lost in translation. Lingonberries anyone?

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by geckzilla » Sun Jan 17, 2016 7:11 am

I've said it before and I'll say it again, the colors are no more a lie than one language translated to another language.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Sun Jan 17, 2016 6:02 am

Nitpicker wrote:I suppose Ann is still able to be thrilled by all the blue light that is captured by black holes. It is a conceptual thing.
Visible and infrared view near newly discovered globular cluster VVV CL001.
ESO/D. Minniti/VVV Team and Digitized Sky Survey 2.
Acknowledgement: Davide De Martin
Ever since Nitpicker wrote that, I have been trying to find a picture to demonstrate that in the world of mapped color, blue can indeed be red.

Take a look at the picture at left, which shows comparison views in visible and infrared light near a newly discovered globular cluster. To me there can be no question that the infrared view (below) is not only more detailed and interesting, but it is also more beautiful. Alas, the colors are (mostly) a lie. Take a look at the brightest star at left in the infrared image. The star looks mostly white, but also faintly bluish. The same star can be identified in the visible star field. Now the infrared-bluish star is the most orange-colored of the reasonably bright stars in the visible field.

Conceivably, the infrared-bluish visibly-orange star could still be intrinsically bluish. It could be a hot star that is severely reddened by dust. Chances are that the bluish-infrared star is genuinely orange in visible light, though.
Image
Infrared Betelgeuse.
NASA/JPL-Caltech/WISE Team.
In the world of infrared photography, a star like Betelgeuse might look brilliantly blue.

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Chris Peterson » Mon Jan 11, 2016 4:15 pm

Ann wrote:But bars are typically poor in gas and dust. They are usually collection of old yellow stars. Stars are point sources, more or less. Couldn't they maintain highly eccentric orbits?
Not over a long period. Dust isn't the issue, and for the most part, neither is gas. It's the stars themselves that perturb one another, and over time destroy high eccentricity orbits. And bars are found in a region of high stellar density.
And what about the dust lanes in bars? Practically all barred galaxies, at least those with any sort of significant star formation, have dust lanes along their bars. If stars in the bar follow relatively circular orbits around the center of the galaxy, they must keep crossing the dust lanes in the bar. Wouldn't that tend to destroy the dust lanes? Alternatively, wouldn't it change the orbits of the stars?

Or is it the other way round, so that the more or less circular orbits of the star in bar actually create the dust lanes in the bar, in a manner similar to the way the cumulative movement of a lot of stars in the disk of a galaxy creates a density wave that gives rise to spiral arms?
I would think that everything in circular orbits would be the most stable. Dust and gas shouldn't affect stellar orbits, but certainly, the stars could potentially redistribute gas and dust. But if everything is in circular orbits, it stays together with much less perturbation.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Mon Jan 11, 2016 3:24 pm

Chris wrote:
I wouldn't assume we can extend a possible explanation for a double nucleus (which is of a scale orders of magnitude smaller than a bar, and possibly orders of magnitude shorter duration) to the mechanism behind a bar.
Okay. I certainly don't know enough orbital mechanics to argue about that.
Like I said, we don't normally see dense clouds of particles maintain highly eccentric orbits. That's a dynamically unstable situation.
But bars are typically poor in gas and dust. They are usually collections of old yellow stars. Stars are point sources, more or less. Couldn't they maintain highly eccentric orbits?

And what about the dust lanes in bars? Practically all barred galaxies, at least those with any sort of significant star formation, have dust lanes along their bars. If stars in the bar follow relatively circular orbits around the center of the galaxy, they must keep crossing the dust lanes in the bar. Wouldn't that tend to destroy the dust lanes? Alternatively, wouldn't it change the orbits of the stars?

Or is it the other way round, so that the more or less circular orbits of the star in bar actually create the dust lanes in the bar, in a manner similar to the way the cumulative movement of a lot of stars in the disk of a galaxy creates a density wave that gives rise to spiral arms?

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Chris Peterson » Mon Jan 11, 2016 3:00 pm

Ann wrote:
Chris Peterson wrote:A couple of points. First, a slightly pedantic one- all closed orbits are elliptical (including perfectly circular ones). What you're discussing is eccentricity. Second, I'm doubtful that the stars, particularly in the center of a galaxy, have very eccentric orbits. There are dynamical mechanisms that work to circularize orbits in dense regions. Perturbations may briefly increase eccentricity, but the orbits will probably circularlize rather quickly, with a new orbital radius (or semimajor axis). The density structure that we call a bar suggests orbital resonances, but not what I'd call a synchronization of eccentricities in any way.
Scott Tremaine has proposed that the observed double nucleus could be explained if P1 is the projection of a disk of stars in an eccentric orbit around the central black hole.[76] The eccentricity is such that stars linger at the orbital apocenter, creating a concentration of stars.
I wouldn't assume we can extend a possible explanation for a double nucleus (which is of a scale orders of magnitude smaller than a bar, and possibly orders of magnitude shorter duration) to the mechanism behind a bar.

Like I said, we don't normally see dense clouds of particles maintain highly eccentric orbits. That's a dynamically unstable situation.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by rstevenson » Mon Jan 11, 2016 12:01 pm

bystander wrote:
rstevenson wrote:Trying to see the full image, I got...
The image “http://imgsrc.hubblesite.org/hu/db/imag ... ll_jpg.jpg” cannot be displayed because it contains errors.
I was getting that last night, but I just tried it and was able to load it with no problems. Maybe your browser is running out of available memory. Try downloading the image and opening it with another image viewer.
As far as I know, my browser (latest Firefox) has access to as much of the system memory (8GB in total) as it needs, whenever it needs it. And being a knowledgeable computer user from Way Back, I did try to download the image without viewing it in the browser, but got the same error code. At any rate, the image is now viewable in the usual way.

Rob

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Mon Jan 11, 2016 6:43 am

Chris Peterson wrote:
Ann wrote:I think that basically two things are happening. First and most importantly, the orbits of the stars near the center of the galaxy start following elliptical (elongated) orbits around the center of the galaxy. They then synchronize their orbits so that all or most stars in that part of the galaxy follow more or less the same elliptical orbit.
A couple of points. First, a slightly pedantic one- all closed orbits are elliptical (including perfectly circular ones). What you're discussing is eccentricity. Second, I'm doubtful that the stars, particularly in the center of a galaxy, have very eccentric orbits. There are dynamical mechanisms that work to circularize orbits in dense regions. Perturbations may briefly increase eccentricity, but the orbits will probably circularlize rather quickly, with a new orbital radius (or semimajor axis). The density structure that we call a bar suggests orbital resonances, but not what I'd call a synchronization of eccentricities in any way.
Wikipedia wrote:
In 1991 Tod R. Lauer used WFPC, then on board the Hubble Space Telescope, to image M31's inner nucleus. The nucleus consists of two concentrations separated by 1.5 parsecs (4.9 ly). The brighter concentration, designated as P1, is offset from the center of the galaxy. The dimmer concentration, P2, falls at the true center of the galaxy and contains a black hole measured at 3–5 × 107 M☉ in 1993,[73] and at 1.1–2.3 × 108 M☉ in 2005.[74] The velocity dispersion of material around it is measured to be ≈ 160 km/s.[75]

Scott Tremaine has proposed that the observed double nucleus could be explained if P1 is the projection of a disk of stars in an eccentric orbit around the central black hole.[76] The eccentricity is such that stars linger at the orbital apocenter, creating a concentration of stars.
Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Chris Peterson » Mon Jan 11, 2016 5:46 am

Ann wrote:I think that basically two things are happening. First and most importantly, the orbits of the stars near the center of the galaxy start following elliptical (elongated) orbits around the center of the galaxy. They then synchronize their orbits so that all or most stars in that part of the galaxy follow more or less the same elliptical orbit.
A couple of points. First, a slightly pedantic one- all closed orbits are elliptical (including perfectly circular ones). What you're discussing is eccentricity. Second, I'm doubtful that the stars, particularly in the center of a galaxy, have very eccentric orbits. There are dynamical mechanisms that work to circularize orbits in dense regions. Perturbations may briefly increase eccentricity, but the orbits will probably circularlize rather quickly, with a new orbital radius (or semimajor axis). The density structure that we call a bar suggests orbital resonances, but not what I'd call a synchronization of eccentricities in any way.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Mon Jan 11, 2016 5:15 am

quigley wrote:Thank you Ann and Neufer for the great explanations of the origins of galactic bars. Upon viewing this image, the first question that came to mind was, "What causes such distinctive formations to occur?" You answered that. So the spiral arms "peel" off stars from the ends of the bars over time?
Again, I'm not the best person to elaborate, but...
I think that basically two things are happening. First and most importantly, the orbits of the stars near the center of the galaxy start following elliptical (elongated) orbits around the center of the galaxy. They then synchronize their orbits so that all or most stars in that part of the galaxy follow more or less the same elliptical orbit. Think of it like this. An elliptical orbit could be "lying down" or "standing up". To get a bar, all or most of the stars in the bar must orbit in the same direction, "lying down" or "standing up". The stars do indeed synchronize their orbits.
NGC 1097. ESA/Hubble & NASA




Another very important thing about barred galaxies is that they have dust lanes running from a little ring in their centers out along the bar all the way to the first spiral arm. On one side, the dust lane is running "above" the bar (not really, but sort of) and on the other side, it is running "below" the bar. Personally I don't understand math, but I will hazard a guess that the dust lanes along the bar are "shepherding" the stars in the bar along their elliptical orbits.

I believe that the dust lanes also move starmaking material like gas and dust into two places in a barred galaxy: it is sent into the ring around the nucleus, where we often find a lot of star formation in barred galaxies. And it is sent to the ends of the bar. Here we often find star formation, too. I believe that star formation at the ends of a bar will make that bar grow in size.
NGC 936. Photo: SDSS.
So what happens when a barred galaxy stops making new stars? That happens when the galaxy has used up its available gas and dust, or when the gas and dust becomes too turbulent to settle down into star making. Well, for one thing, the dust lanes probably disappear from the bar, because the dust lanes are the mechanisms for funneling star making material into the ring around the nucleus and to the ends of the bar.

NGC 936 is a barred galaxy that gave up star formation long ago. It is a very "red and dead" galaxy. But you can still see a "ring" around its nucleus, and you can see that there used to be quite a lot of star formation at the ends of the bar. The bar ends are bright.

And that's what I can say about the formation of bars, I think.

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by quigley » Mon Jan 11, 2016 12:39 am

Thank you Ann and Neufer for the great explanations of the origins of galactic bars. Upon viewing this image, the first question that came to mind was, "What causes such distinctive formations to occur?" You answered that. So the spiral arms "peel" off stars from the ends of the bars over time?

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Sun Jan 10, 2016 7:17 am

Nitpicker wrote:I suppose Ann is still able to be thrilled by all the blue light that is captured by black holes. It is a conceptual thing.
Actually, no. When it comes to astronomy, I get my biggest kicks out of seeing blue objects that I know (or believe) are blue for real. If I know that an image is a false-color (or mapped color) one, seeing blue objects in it doesn't make me happy, because then I know that the blue objects aren't blue for real.

I remember reading about cool white dwarfs that get bluer again as they keep cooling. I was horribly disappointed when I found that these white dwarfs, instead of actually getting bluer as they get cooler, are becoming less infrared than they "should" be when they have reached a certain temperature. The energy that ought to have been emitted by the white dwarf as certain wavelengths of infrared light instead gets shifted into the red part of the visual spectrum. So these stars become considerably brighter in red light yet fainter in infrared light as they get cooler. And because red is a "bluer" color than infrared - that is, it is a more short-wave color than infrared - these stars actually get "blue" again when they get red again! I was horribly disappointed!

But of course, if a mapped color image like in the High Energy Andromeda APOD shows a lot of yellow sources and one blue one, then I'd like to know why that "blue" object is differently colored than the rest of them, and what real, physical properties it has that sets it apart from the others.

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Chris Peterson » Sun Jan 10, 2016 6:23 am

ta152h0 wrote:How can you tell the difference between blue light due to red shift or actual blue emissions ?
By visual inspection, you can't for sure. You may know something about what the object should look like, and therefore recognize of there is a large redshift, but you can't count on that. From the standpoint of scientific analysis, you can tell the difference because you aren't looking at "color", but at the spectral structure of the light. In most cases, that means identifying specific spectral lines (like those of hydrogen) that are measured at a different wavelength than we know they are actually at. From that the precise red (or blue) shift can be determined. In other cases, the spectrum shows a particular shape (such as a blackbody curve) that will be uniquely shifted- in such cases it is possible to measure the shift by looking at the intensity ratios of two or more parts of the spectrum.

Visually, redshifted objects are not necessarily redder, and blueshifted objects are not necessarily bluer than they would otherwise appear (although in many cases they are, especially for fairly small shifts).

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by geckzilla » Sun Jan 10, 2016 4:35 am

ta152h0 wrote:How can you tell the difference between blue light due to red shift or actual blue emissions ?
By knowing how far away what you're looking at is.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by ta152h0 » Sun Jan 10, 2016 4:17 am

How can you tell the difference between blue light due to red shift or actual blue emissions ?

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Nitpicker » Sun Jan 10, 2016 1:08 am

I suppose Ann is still able to be thrilled by all the blue light that is captured by black holes. It is a conceptual thing.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Beyond » Sat Jan 09, 2016 11:07 pm

Yes, if you get to close to a black hole, you could end up very black and blue!

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Chris Peterson » Sat Jan 09, 2016 10:59 pm

neufer wrote:
Ann wrote:And what about the central black hole of NGC 1300?
Color Commentators aren't authorized to discuss black holes...out of their jurisdiction.
Black is the new blue.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by neufer » Sat Jan 09, 2016 10:50 pm

Ann wrote:
And what about the central black hole of NGC 1300?
Color Commentators aren't authorized to discuss black holes...out of their jurisdiction.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Ann » Sat Jan 09, 2016 8:34 pm

Wikipedia wrote:
Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Barred spiral galaxies with high mass accumulated in their center tend to have short, stubby bars.
I guess the bar of NGC 1300 isn't that massive, then, since it hasn't collapsed under its own weight. It does have a very low surface brightness.

And what about the central black hole of NGC 1300?

According to Supermassive black hole mass measurements for NGC 1300 and NGC2748 based on HST emission-line gas kinematics the central black hole of NGC 1300 most likely has a mass of around 66 million solar masses. That's a lot, more than ten times the mass of the central black hole of the Milky Way, but it is very, very far from being any sort of record holder. In fact the central black hole of Andromeda might be heavier.

Ann

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by neufer » Sat Jan 09, 2016 4:38 pm

https://en.wikipedia.org/wiki/Barred_spiral_galaxy wrote: <<Up to two-thirds of all spiral galaxies contain a bar. The current hypothesis is that the bar structure acts as a type of stellar nursery, fueling star birth at their centers. The bar is thought to act as a mechanism that channels gas inwards from the spiral arms through orbital resonance, in effect funneling the flow to create new stars. This process is also thought to explain why many barred spiral galaxies have active galactic nuclei, such as that seen in the Southern Pinwheel Galaxy. :arrow:

The creation of the bar is generally thought to be the result of a density wave radiating from the center of the galaxy whose effects reshape the orbits of the inner stars. This effect builds over time to stars orbiting further out, which creates a self-perpetuating bar structure.

Bars are thought to be temporary phenomena in the lives of spiral galaxies; the bar structures decay over time, transforming galaxies from barred spirals to more "regular" spiral patterns. Past a certain size the accumulated mass of the bar compromises the stability of the overall bar structure. Barred spiral galaxies with high mass accumulated in their center tend to have short, stubby bars. Since so many spiral galaxies have bar structures, it is likely that they are recurring phenomena in spiral galaxy development. The oscillating evolutionary cycle from spiral galaxy to barred spiral galaxy is thought to take on the average about two billion years.

Recent studies have confirmed the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts.>>
https://en.wikipedia.org/wiki/Mos_Eisley_Cantina wrote:
<<The Chalmun's Cantina (often called the Mos Eisley Cantina) is a fictional bar of the Star Wars universe located in the "pirate city" of Mos Eisley on the planet Tatooine. It is the haunt of freight pilots and other dangerous characters of various alien races and contains booths, a bar counter, and some free-standing tables, and sometimes a band of musicians named Figrin D'an and the Modal Nodes. The establishment is extremely rough in nature, and the clientele and the management give incidents of deadly violence no more than a moment's attention. Droids are not allowed inside; a droid detector near the front door alerts the management of any entering droid.>>
https://en.wikipedia.org/wiki/Star_Wars:_The_Force_Awakens#Cast wrote:
<<Maz Kanata: A wise and perceptive figure operating a somewhat shady cantina on the peaceful forest planet, Takodana. J.J. Abrams said Kanata has "lived over a thousand years. She's had this watering hole … and it's like another bar that you'd find in a corner of the Star Wars universe." According to Abrams, the character was based on his former high school English teacher, Rose Gilbert, who lectured at the Palisades Charter High School from 1961 to 2013. "I mentioned Rose in an early story meeting as a sort of timeless, wise figure that I'd actually known in my life.">>

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by Steve Dutch » Sat Jan 09, 2016 3:52 pm

What's especially neat is that you can look THROUGH NGC 1300 to distant galaxies beyond it.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by bystander » Sat Jan 09, 2016 3:33 pm

rstevenson wrote:Trying to see the full image, I got...
The image “http://imgsrc.hubblesite.org/hu/db/imag ... ll_jpg.jpg” cannot be displayed because it contains errors.
Rob
I was getting that last night, but I just tried it and was able to load it with no problems. Maybe your browser is running out of available memory. Try downloading the image and opening it with another image viewer.

Re: APOD: Barred Spiral Galaxy NGC 1300 (2016 Jan 09)

by rstevenson » Sat Jan 09, 2016 3:09 pm

Trying to see the full image, I got...
The image “http://imgsrc.hubblesite.org/hu/db/imag ... ll_jpg.jpg” cannot be displayed because it contains errors.
Rob

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