APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

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Expand view Topic review: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Thu Mar 03, 2016 12:47 am

DavidLeodis wrote:
Ann wrote:
DavidLeodis wrote:I found it odd that on clicking the APOD image (to get a larger version) the image brought up is switched over horizontally! :?

I'm wondering if there is anything known about the jet-like feature that goes out about to the top left corner in the APOD image (about to the top right corner in the clicked on version)?
The larger version is oriented so that north is up, which is the conventional orientation.

I'm afraid I don't know anything about that jet. But NGC 3310 is known as the Bow and Arrow galaxy, because of that jet and the arc-like feature is it crossing.

Ann
Thanks for your help Ann, which is appreciated :).

Before submitting my query I had searched under NGC 3310 but (without going through too many links) none of them mentioned the Bow and Arrow galaxy and it was only when I searched under Bow and Arrow after your information that I finally found some mentions. Unless you already knew of it I hope therefore that you did not spend too much time and effort in your willingness to help me.
Don't worry! :D

I love galaxies, and NGC 3310 is among my very favorite galaxies. I already knew it was called the Bow and Arrow galaxy.

Ann

EGSY8p7: A Starburst Spiral Galaxy?

by neufer » Wed Mar 02, 2016 7:57 pm

https://en.wikipedia.org/wiki/EGSY8p7 wrote: <<EGSY8p7 is a distant galaxy, with a spectroscopic redshift of z = 8.68, a light travel distance of 13.2 billion light-years from Earth and observed as it existed 570 million years after the Big Bang. In July 2015, EGSY8p7 was announced as the oldest and most-distant known object.

The light of the EGSY8p7 galaxy appears to have been magnified twofold by gravitational lensing in the light's travel to Earth, enabling detecting EGSY8p7, which would not have been possible without the magnification. EGSY8p7's distance from Earth was determined by measuring the redshift of Lyman-alpha emissions. EGSY8p7 is the most distant known detection of hydrogen's Lyman-alpha emissions. The distance of this detection was surprising, because neutral hydrogen (atomic hydrogen) clouds filling the early universe should have absorbed these emissions, even by some hydrogen cloud sources closer to Earth, according to the standard cosmological model. A possible explanation for the detection would be that reionization progressed in a "patchy" manner, rather than homogeneously throughout the universe, creating patches where the EGSY8p7 hydrogen Lyman-alpha emissions could travel to Earth, because there were no neutral hydrogen clouds to absorb the emissions.>>

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by DavidLeodis » Wed Mar 02, 2016 7:46 pm

Ann wrote:
DavidLeodis wrote:I found it odd that on clicking the APOD image (to get a larger version) the image brought up is switched over horizontally! :?

I'm wondering if there is anything known about the jet-like feature that goes out about to the top left corner in the APOD image (about to the top right corner in the clicked on version)?
The larger version is oriented so that north is up, which is the conventional orientation.

I'm afraid I don't know anything about that jet. But NGC 3310 is known as the Bow and Arrow galaxy, because of that jet and the arc-like feature is it crossing.

Ann
Thanks for your help Ann, which is appreciated :).

Before submitting my query I had searched under NGC 3310 but (without going through too many links) none of them mentioned the Bow and Arrow galaxy and it was only when I searched under Bow and Arrow after your information that I finally found some mentions. Unless you already knew of it I hope therefore that you did not spend too much time and effort in your willingness to help me.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 5:34 pm

Visual_Astronomer wrote:Color is created in the brain. There is no such thing as color in the world outside of your head.

Color in an astronomical photo can be rendered aesthetically pleasing, and if it also conveys some scientifically useful data, all the better. But there is no vantage point in space where you could look at this galaxy with your naked eye and see colors like in this photograph.
Exactly my point throughout this discussion.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Visual_Astronomer » Wed Mar 02, 2016 5:26 pm

Chris Peterson wrote:
Ann wrote:I don't understand you, Chris. Are you saying that the Travis Rector APOD shows "accurate color" while Adam Block's RGB image is "unnatural"?
I'm saying that it's entirely possible that the Rector image shows more accurate color than the Block image. There's no way that I can make that assessment conclusively just looking at the images, however.

Specifically, though, what I was arguing was that an image that displayed photometric color as actual color would require a very carefully constructed false color palette. That is, an image that showed a star's temperature or B-V value as a particular RGB value. It would be a useful image, but nothing close to what could be called accurate color.
Color is created in the brain. There is no such thing as color in the world outside of your head.

Color in an astronomical photo can be rendered aesthetically pleasing, and if it also conveys some scientifically useful data, all the better. But there is no vantage point in space where you could look at this galaxy with your naked eye and see colors like in this photograph.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 4:07 pm

DavidLeodis wrote:I found it odd that on clicking the APOD image (to get a larger version) the image brought up is switched over horizontally! :?

I'm wondering if there is anything known about the jet-like feature that goes out about to the top left corner in the APOD image (about to the top right corner in the clicked on version)?
The larger version is oriented so that north is up, which is the conventional orientation.

I'm afraid I don't know anything about that jet. But NGC 3310 is known as the Bow and Arrow galaxy, because of that jet and the arc-like feature is it crossing.

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by DavidLeodis » Wed Mar 02, 2016 2:52 pm

I found it odd that on clicking the APOD image (to get a larger version) the image brought up is switched over horizontally! :?

I'm wondering if there is anything known about the jet-like feature that goes out about to the top left corner in the APOD image (about to the top right corner in the clicked on version)?

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 6:22 am

Ann wrote:Travis Rector's image looks "flat" to me, where all the colors are strongly separated and remain one and the same hue. It sort of resembles the old Dick Tracy movie. Look at the pink Ha features in the Travis Rector image. They are exactly the same shade of pink everywhere. Adam Block's image, however, shows that the Ha regions are more or less mixed with blue starlight. Some Ha regions are all pink in his image, others are purple, and others show a mixture of pink, white, purple and blue. This is exactly what we should expect. In some Ha regions the stars are completely embedded, and the nebula will look all pink. In others the stars are partly or fully revealed and contribute blue light to the nebula.

An unexplained feature of Travis Rector's image is the beige swath of galactic disk stretching from 3 o'clock to 9 o'clock in the image. Like Geck said, this might contain an interesting piece of information about the presence or absence of dust in the disk. But we can only guess at what causes this beige color, since nothing is explained.
You see things differently than I do. I see as much range in the Ha color in the Rector image as in the Block image. I think the Ha color is more natural in the Rector image- it's quite oversaturated in the Block image. That creates a color distortion that makes subtle variation more obvious (which is one reason to process this way), but the range is present in both. And all of the blue in the Block image is very unnatural- not at all the color of blue stars. Again, oversaturated. The Rector image looks quite natural to me- the pale blue of hot stars fading to white as we go into the center, but with pink added by the central hydrogen regions. I don't see anything beige, and so I'm not sure what this "swath" you're referring to is.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 1:55 am

Chris Peterson wrote:
Ann wrote:I don't understand you, Chris. Are you saying that the Travis Rector APOD shows "accurate color" while Adam Block's RGB image is "unnatural"?
I'm saying that it's entirely possible that the Rector image shows more accurate color than the Block image. There's no way that I can make that assessment conclusively just looking at the images, however.
Travis Rector's image looks "flat" to me, where all the colors are strongly separated and remain one and the same hue. It sort of resembles the old Dick Tracy movie. Look at the pink Ha features in the Travis Rector image. They are exactly the same shade of pink everywhere. Adam Block's image, however, shows that the Ha regions are more or less mixed with blue starlight. Some Ha regions are all pink in his image, others are purple, and others show a mixture of pink, white, purple and blue. This is exactly what we should expect. In some Ha regions the stars are completely embedded, and the nebula will look all pink. In others the stars are partly or fully revealed and contribute blue light to the nebula.

An unexplained feature of Travis Rector's image is the beige swath of galactic disk stretching from 3 o'clock to 9 o'clock in the image. Like Geck said, this might contain an interesting piece of information about the presence or absence of dust in the disk. But we can only guess at what causes this beige color, since nothing is explained.

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 1:42 am

Ann wrote:I don't understand you, Chris. Are you saying that the Travis Rector APOD shows "accurate color" while Adam Block's RGB image is "unnatural"?
I'm saying that it's entirely possible that the Rector image shows more accurate color than the Block image. There's no way that I can make that assessment conclusively just looking at the images, however.

Specifically, though, what I was arguing was that an image that displayed photometric color as actual color would require a very carefully constructed false color palette. That is, an image that showed a star's temperature or B-V value as a particular RGB value. It would be a useful image, but nothing close to what could be called accurate color.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 1:25 am

Chris Peterson wrote:
Ann wrote:Thanks, Chris, that's interesting. I particularly appreciate the illustration.

Nevertheless, I think we have very good reasons to think that the outer parts of NGC 3310 are different than the inner spiral arms when it comes to stellar content. The populations in the inner arms are more dominated by short-wave light than the populations in the outer parts. Shouldn't that fact be recognized when making a color picture of that galaxy?
That would, however, be a very unnatural sort of image, requiring a complex false-color palette. You would essentially be mapping the photometric colors to display colors.
Alternatively, if the photographer wanted to create an image that would mimic what would be the typical human color response to the galaxy, if our eyes were sensitive enough to clearly see color in the outer parts of a galaxy, shouldn't that be stated in the caption?
I looked earlier to see how this image was made, and had no more luck than Geck.

Still, an image that is designed to mimic human color vision is usually called "true color" or "accurate color", and it's generally what we assume a color astronomical image is unless otherwise specified.
I don't understand you, Chris. Are you saying that the Travis Rector APOD shows "accurate color" while Adam Block's RGB image is "unnatural"?

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 1:22 am

Ann wrote:Thanks, Chris, that's interesting. I particularly appreciate the illustration.

Nevertheless, I think we have very good reasons to think that the outer parts of NGC 3310 are different than the inner spiral arms when it comes to stellar content. The populations in the inner arms are more dominated by short-wave light than the populations in the outer parts. Shouldn't that fact be recognized when making a color picture of that galaxy?
That would, however, be a very unnatural sort of image, requiring a complex false-color palette. You would essentially be mapping the photometric colors to display colors.
Alternatively, if the photographer wanted to create an image that would mimic what would be the typical human color response to the galaxy, if our eyes were sensitive enough to clearly see color in the outer parts of a galaxy, shouldn't that be stated in the caption?
I looked earlier to see how this image was made, and had no more luck than Geck.

Still, an image that is designed to mimic human color vision is usually called "true color" or "accurate color", and it's generally what we assume a color astronomical image is unless otherwise specified.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 1:17 am

Chris Peterson wrote:
Ann wrote:
Chris wrote:
Do not confuse astronomical "blue" (a ratio of filtered intensities) with visual "blue".
Is it at all useful to talk about "visual 'blue'" when it comes to the outer parts of galaxies? Aren't they so faint that they would generate no color response to the human eye whatsoever?
Well, yes, I think so. Because ultimately we're seeing the color visually, whether directly or in an image. Here's a virtual galaxy, with every "star" in it exactly the same hue- the same blue content, and all that is changing is the brightness, which changes the visual saturation. If you were examining this spectroscopically, you'd find that every star was the same temperature, and all that was changing was the intensity.
blue.jpg
Visually, we operate with a certain dynamic range- a range that is greatly narrowed when we view an image on the monitor (which is why some kind of transfer function is normally applied to compress the actual range into what our displays can output).
Ann wrote:
Chris wrote:
I'd expect the blue saturation to be high on the outside and low on the inside, even though the individual stars have the same photometric blueness.
Still, I'm willing to at least consider the possibility that "maximum blueness" might be reached in stars of spectral classes B0, O9 and O8.
Visually, "maximum blueness" has little to do with the the spectral class. It's mostly a function of intensity. A star in any of these classes will range in color from black, through some kind of blue, and end up white.
It is however absurd to claim that A-type stars and cool B-type stars are as blue as the hottest B-type stars and late O-type stars. That is very obviously not true. A-type stars are pretty common, so many are nearby, and it is overwhelmingly clear that they so rarely have a more negative B-V index than -0.01, and hardly ever as negative as -0.10.
Again, the B-V index is a very poor indicator of visual color.
Thanks, Chris, that's interesting. I particularly appreciate the illustration.

Nevertheless, I think we have very good reasons to think that the outer parts of NGC 3310 are different than the inner spiral arms when it comes to stellar content. The populations in the inner arms are more dominated by short-wave light than the populations in the outer parts. Shouldn't that fact be recognized when making a color picture of that galaxy?

Alternatively, if the photographer wanted to create an image that would mimic what would be the typical human color response to the galaxy, if our eyes were sensitive enough to clearly see color in the outer parts of a galaxy and to be almost blinded by the inner spiral arms, shouldn't that be stated in the caption?

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 1:16 am

MarkBour wrote:Okay, I'm trying *not* to be controversial here, but I always have contrarian leanings, so bear with me. We have lots of evidence of the existence of "dark matter". That is, sources of gravitation in and around galaxies beyond the normal matter we can observe through our scopes (so I hear). And we can certainly see lots of examples of structure in galaxies that show the evidence of collisions or encounters. These evidences are all gravitational as far as I've read.

It seems to me that:

a. When galaxies collide, it will be their dark matter interacting as much or sometimes even more than the visible matter. (For example, we may start to experience the influence of Andromeda's dark matter long before the galaxy we can see actually gets to our doorstep.)
If you're talking about gravitational interaction, that's true. But much of the interaction we observe in colliding galaxies isn't gravitational, but is electromagnetic. Dark matter won't be involved in that. The dark matter halo around a galaxy is not a lot larger than the longest dimension of the luminous matter. Andromeda's dark matter halo won't directly collide with our galaxy's dark matter halo until the two galaxies are very close.
b. If it can move and collect in its own way, then a clump of dark matter could easily give rise to a galactic starburst all on its own, if it moved through the galaxy.
Yes, assuming a free clump of dark matter. We don't see a lot of evidence those exist, however. If they did, we'd probably see a lot of otherwise unexplainable gravitational lensing.
c. Here I'm getting pretty speculative: It seems possible that a large body of dark matter, alone in space, could give rise to a galaxy.
While galaxy formation remains poorly understood, most models depend heavily upon dark matter. But this happened long ago. Galaxies are no longer being formed.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Wed Mar 02, 2016 1:05 am

Ann wrote:
Chris wrote:
Do not confuse astronomical "blue" (a ratio of filtered intensities) with visual "blue".
Is it at all useful to talk about "visual 'blue'" when it comes to the outer parts of galaxies? Aren't they so faint that they would generate no color response to the human eye whatsoever?
Well, yes, I think so. Because ultimately we're seeing the color visually, whether directly or in an image. Here's a virtual galaxy, with every "star" in it exactly the same hue- the same blue content, and all that is changing is the brightness, which changes the visual saturation. If you were examining this spectroscopically, you'd find that every star was the same temperature, and all that was changing was the intensity.
blue.jpg
blue.jpg (49.11 KiB) Viewed 5130 times
Visually, we operate with a certain dynamic range- a range that is greatly narrowed when we view an image on the monitor (which is why some kind of transfer function is normally applied to compress the actual range into what our displays can output).
Ann wrote:
Chris wrote:
I'd expect the blue saturation to be high on the outside and low on the inside, even though the individual stars have the same photometric blueness.
Still, I'm willing to at least consider the possibility that "maximum blueness" might be reached in stars of spectral classes B0, O9 and O8.
Visually, "maximum blueness" has little to do with the the spectral class. It's mostly a function of intensity. A star in any of these classes will range in color from black, through some kind of blue, and end up white.
It is however absurd to claim that A-type stars and cool B-type stars are as blue as the hottest B-type stars and late O-type stars. That is very obviously not true. A-type stars are pretty common, so many are nearby, and it is overwhelmingly clear that they so rarely have a more negative B-V index than -0.01, and hardly ever as negative as -0.10.
Again, the B-V index is a very poor indicator of visual color.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 12:47 am

geckzilla wrote:Ann, I would guess that this image is comprised of infrared data. Of course, there isn't any technical information available on what data was used to create the image, so I would also guess that perhaps Travis simply made it this way because it was visually appealing to him.
Thanks, Geck. That sounds extremely plausible.

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 12:46 am

MarkBour wrote:Okay, I'm trying *not* to be controversial here, but I always have contrarian leanings, so bear with me. We have lots of evidence of the existence of "dark matter". That is, sources of gravitation in and around galaxies beyond the normal matter we can observe through our scopes (so I hear). And we can certainly see lots of examples of structure in galaxies that show the evidence of collisions or encounters. These evidences are all gravitational as far as I've read.

It seems to me that:
  1. When galaxies collide, it will be their dark matter interacting as much or sometimes even more than the visible matter. (For example, we may start to experience the influence of Andromeda's dark matter long before the galaxy we can see actually gets to our doorstep.)
  2. If it can move and collect in its own way, then a clump of dark matter could easily give rise to a galactic starburst all on its own, if it moved through the galaxy.
  3. Here I'm getting pretty speculative: It seems possible that a large body of dark matter, alone in space, could give rise to a galaxy.
I welcome any reactions to this thinking.
Mark, I wish I had more time to respond to this. An interesting discussion about dark matter, galaxies and voids is found here.

I think you should read about the Bullet Cluster, too. Very interesting.

Although most galaxies are found in large or small clusters or groups, some are isolated and exist in cosmic voids. One such galaxy is NGC 2683. What part did dark matter play in forming that galaxy? I have no idea. NGC 2683 is smaller than the Milky Way and has low levels of star formation. But I'm all but certain that I have read about at least one very large galaxy in a cosmic void.

I believe dark matter can be quite clumpy. I found this picture, which is pretty useless, since it didn't come with a caption to explain it. Nevertheless, it does suggest the possibility that dark matter can come in clumps that just might collide with something. But I don't know how prone dark matter is to "flying around".

In this post, I discuss the possibility that massive open cluster NGC 6231 might have formed when globular cluster NGC 6397 collided with the plane of the Milky Way.

That's all I can come up with for now. Gotta go!

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by geckzilla » Wed Mar 02, 2016 12:44 am

Ann, I would guess that this image is comprised of infrared data. Of course, there isn't any technical information available on what data was used to create the image, so I would also guess that perhaps Travis simply made it this way because it was visually appealing to him.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Ann » Wed Mar 02, 2016 12:27 am

APOD Robot wrote:
The featured image from the Gemini North Telescope shows the galaxy in great detail, color-coded so that pink highlights gas while white and blue highlight stars.
This is a very imprecise piece of information. Which stars are color-coded white and which stars are color-coded blue?
Chris wrote:
Do not confuse astronomical "blue" (a ratio of filtered intensities) with visual "blue".
Is it at all useful to talk about "visual 'blue'" when it comes to the outer parts of galaxies? Aren't they so faint that they would generate no color response to the human eye whatsoever?
Chris wrote:
I'd expect the blue saturation to be high on the outside and low on the inside, even though the individual stars have the same photometric blueness.
They don't have the same photometric blueness. I have spent hours after hours checking up the B-V color of thousands of A-, B- and O-type stars. The bluest stars (the ones with the most negative O-B index, around -0.25 or so) are typically stars of spectral classes around B0, O9 and O8. Still hotter O-type stars are usually less blue, but there is a reason for that. The hottest and most massive O-type stars are so rare that they are typically so far away that they are always significantly dust-reddened. Still, I'm willing to at least consider the possibility that "maximum blueness" might be reached in stars of spectral classes B0, O9 and O8.

It is however absurd to claim that A-type stars and cool B-type stars are as blue as the hottest B-type stars and late O-type stars. That is very obviously not true. A-type stars are pretty common, so many are nearby, and it is overwhelmingly clear that they so rarely have a more negative B-V index than -0.01, and hardly ever as negative as -0.10.

Adam Block's image strongly suggests that the outer features of NGC 3310 are dominated by old and intermediate stars, which are non-blue in color. So the outer parts of NGC 3310 may be dominated by the light of stars of spectral classes F, G and K. Many galaxies have halos dominated by non-blue stars, so it would be no surprise whatsoever if this was true for NGC 3310.

And the bluest parts of NGC 3310 are found in its inner arms. Why should that fact not be respected? Why should the visual rendering of this galaxy be tweaked to resemble what we would see if we were almost blinded by the brilliance of spiral arms dominated by the light of OB stars, but could see and enjoy the color of the outer parts dominated by A-type stars? Galaxies are faint objects, the stars are always far apart, and the outer parts of galaxies are exceedingly faint. We are frankly never blinded by the brilliant light of galaxies.

The blue and white colors in this image are rendered in a way that doesn't let us see or understand why they look they way they do. There seems to be no scientific reasoning behind it. To talk about something as imprecise as visual color response in most humans is nonsensical in my opinion when it comes to an object as visually faint as a galaxy.

Ann

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by geckzilla » Tue Mar 01, 2016 10:19 pm

loquin wrote:So, I noticed the blue 'Theta" (Θ) in the upper-right corner of APOD's image. (Upper left of the APOD display image, upper right of the source image.)
Blue Theta.png
Is this a background elliptical galaxy with a wisp of dense gas/dust from NGC3310 forming the 'bar,' or is the 'bar' associated with the elliptical?

Or, something entirely associated with NGC3310?
I would guess this is actually a foreground star system in our Milky Way. In regards about its appearance of looking like they aren't perfectly round I would say it probably has something to do with some slight diffraction spikes extending the light just enough to make them look a bit squished.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by loquin » Tue Mar 01, 2016 10:01 pm

So, I noticed the blue 'Theta" (Θ) in the upper-right corner of APOD's image. (Upper left of the APOD display image, upper right of the source image.)
Blue Theta.png
Blue Theta.png (56.78 KiB) Viewed 5165 times
Is this a background elliptical galaxy with a wisp of dense gas/dust from NGC3310 forming the 'bar,' or is the 'bar' associated with the elliptical?

Or, something entirely associated with NGC3310?

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by MarkBour » Tue Mar 01, 2016 9:19 pm

Okay, I'm trying *not* to be controversial here, but I always have contrarian leanings, so bear with me. We have lots of evidence of the existence of "dark matter". That is, sources of gravitation in and around galaxies beyond the normal matter we can observe through our scopes (so I hear). And we can certainly see lots of examples of structure in galaxies that show the evidence of collisions or encounters. These evidences are all gravitational as far as I've read.

It seems to me that:
  1. When galaxies collide, it will be their dark matter interacting as much or sometimes even more than the visible matter. (For example, we may start to experience the influence of Andromeda's dark matter long before the galaxy we can see actually gets to our doorstep.)
  2. If it can move and collect in its own way, then a clump of dark matter could easily give rise to a galactic starburst all on its own, if it moved through the galaxy.
  3. Here I'm getting pretty speculative: It seems possible that a large body of dark matter, alone in space, could give rise to a galaxy.
I welcome any reactions to this thinking.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by starsurfer » Tue Mar 01, 2016 6:49 pm

APOD Robot wrote:star-forming party.
Click to play embedded YouTube video.

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by starsurfer » Tue Mar 01, 2016 6:49 pm

Ann wrote:
Chris Peterson wrote:
Ann wrote:As for the image itself, it is weirdly colored for no apparent reason. The pink glow of H-alpha is shown well, but there is no reason to make the galaxy look bluer in its outer parts than in its inner arms. Actually the inner arms are very blue and bursting with O- and B-stars, while the outer parts may contain no O-stars at all and only a few B-stars.
I believe that the image is actually pretty accurate in terms of color. Do not confuse astronomical "blue" (a ratio of filtered intensities) with visual "blue". Color is a physiological response, and for some given blue hue, as the intensity increases the saturation will decrease (that is, the color will approach white- which is why most people see blue stars as cool white). The inner parts of this galaxy are much brighter than the outer parts, so rendered realistically, I'd expect the blue saturation to be high on the outside and low on the inside, even though the individual stars have the same photometric blueness.
NGC 3310. Photo: Adam Block.
As I've said before, this image by Adam Block is by far my favorite portrait of NGC 3310. The outer tidal features are fantastic, and the colors are superb.

Ann
You took the words out of my mouth as well as Adam Block's wonderful image! :evil: :lol2:
Unsurprisingly, the late Halton Arp included NGC 3310 in his atlas of peculiar galaxies as Arp 217. There are way too many impressive peculiar galaxies in Ursa Major!

Re: APOD: NGC 3310: A Starburst Spiral Galaxy (2016 Mar 01)

by Chris Peterson » Tue Mar 01, 2016 6:09 pm

Ann wrote:As I've said before, this image by Adam Block is by far my favorite portrait of NGC 3310. The outer tidal features are fantastic, and the colors are superb.
It may be your favorite. And I agree it's lovely. But that doesn't mean its color is more accurate than today's APOD.

Color is a tricky business.

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