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

[APOD Robot]

NGC 3310: A Starburst Spiral Galaxy

Explanation: The party is still going on in spiral galaxy NGC 3310. Roughly 100 million years ago, NGC 3310 likely collided with a smaller galaxy causing the large spiral galaxy to light up with a tremendous burst of star formation. The changing gravity during the collision created density waves that compressed existing clouds of gas and triggered the star-forming party. 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. Some of the star clusters in the galaxy are quite young, indicating that starburst galaxies may remain in star-burst mode for quite some time. NGC 3310 spans about 50,000 light years, lies about 50 million light years away, and is visible with a small telescope towards the constellation of Ursa Major.

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[Ann]

This image has won a poll. NGC 3310 certainly deserves to be a winner and to get more attention than it usually receives. It is a fantastically starforming, even starbursting galaxy, which nevertheless retains its spiral structure. That it actually unusual. Also the starburst is not confined to the core, but takes place "all over the arms".

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.

Ann

[Boomer12k]

Interesting one, the trail off the top....

Yup, the Partay is goin' on....

Woo, Wooo...

:---[===] *

[AloE]

please clarify the way time is used:

since the galaxy distance is ~50 MLY, does "Roughly 100 million years ago" mean that the collision would have been visible at Earth:

100 million years ago (= this photo is the state of the galaxy ~100 million years after collision thus the collision occurred 150 million years ago and took an additional 50 million more years to become visible at earth), or

50 million years ago (= collision occurred 100m earth years ago but took an additional 50m earth years to be visible by observer on Earth thus this picture is the state of the galaxy only 50 million years after the collision since light we see today is ~ 50m years old)?

Thank you!

[Guest]

Hey, you want a party? Just wait until Andromeda hits home sweet home! Now that will be some party! Wouldn't it be wonderful if there were still people on Earth to whoop it up!

[geckzilla]

please clarify the way time is used:

since the galaxy distance is ~50 MLY, does "Roughly 100 million years ago" mean that the collision would have been visible at Earth:

100 million years ago (= this photo is the state of the galaxy ~100 million years after collision thus the collision occurred 150 million years ago and took an additional 50 million more years to become visible at earth), or

50 million years ago (= collision occurred 100m earth years ago but took an additional 50m earth years to be visible by observer on Earth thus this picture is the state of the galaxy only 50 million years after the collision since light we see today is ~ 50m years old)?

Thank you!

It means it happened 100 million years ago. Astronomers will very typically consider light as it currently reaches Earth to be "now" and disregard the light travel time. There are times when this matters, just not for this. It's confusing and unnecessary.

[Chris Peterson]

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.

[neufer]

Explanation: Roughly 100 million years ago, NGC 3310 likely collided with a smaller galaxy causing the large spiral galaxy to light up with a tremendous burst of star formation.

Google says it bears 'some responsibility' after self-driving car hit bus
By David Shepardson: Reuters/Elijah Nouvelage

[b][color=#0000FF]A prototype of Google's own self-driving vehicle.[/color][/b]

---

<<Alphabet Inc's (GOOGL.O) Google said on Monday it bears "some responsibility" after one of its self-driving cars struck a municipal bus in a minor crash earlier this month.

In a Feb. 23 report filed with California regulators, Google said the crash took place in Mountain View on Feb. 14 when a self-driving Lexus RX450h sought to get around some sandbags in a wide lane.

Google said in the filing the autonomous vehicle was traveling at less than 2 miles per hour, while the bus was moving at about 15 miles per hour.

The vehicle and the test driver "believed the bus would slow or allow the Google (autonomous vehicle) to continue," it said. But three seconds later, as the Google car in autonomous mode re-entered the center of the lane, it struck the side of the bus, causing damage to the left front fender, front wheel and a driver side sensor. No one was injured in the car or on the bus.

Google said it has reviewed this incident "and thousands of variations on it in our simulator in detail and made refinements to our software. From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future.">>

[Ann]

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.

Click to view full size image

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

[Chris Peterson]

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.

[starsurfer]

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.

Click to view full size image

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!
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!

[starsurfer]

star-forming party.

Click to play embedded YouTube video.

[MarkBour]

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.

[loquin]

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 (56.78 KiB) Viewed 5224 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?

[geckzilla]

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.

[Ann]

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

[geckzilla]

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.

[Ann]

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

[Ann]

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

[Chris Peterson]

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 (49.11 KiB) Viewed 5189 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).

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.

[Chris Peterson]

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.

[Ann]

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).

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

[Chris Peterson]

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.

[Ann]

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

[Chris Peterson]

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.