APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

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APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by APOD Robot » Sun Nov 06, 2016 4:11 am

Image Starburst Cluster in NGC 3603

Explanation: A mere 20,000 light-years from the Sun lies NGC 3603, a resident of the nearby Carina spiral arm of our Milky Way Galaxy. NGC 3603 is well known to astronomers as one of the Milky Way's largest star-forming regions. The central open star cluster contains thousands of stars more massive than our Sun, stars that likely formed only one or two million years ago in a single burst of star formation. In fact, nearby NGC 3603 is thought to contain a convenient example of the massive star clusters that populate much more distant starburst galaxies. Surrounding the cluster are natal clouds of glowing interstellar gas and obscuring dust, sculpted by energetic stellar radiation and winds. Recorded by the Hubble Space Telescope, the image spans about 17 light-years.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Ann » Sun Nov 06, 2016 6:59 am

Today's APOD is a golden oldie, and I'm glad to see it again.
Massive young cluster Westerlund 2. Photo:
NASA, ESA, the Hubble Heritage Team (STScI/AURA),
A. Nota (ESA/STScI), and the Westerlund 2 Science Team
The Milky Way is very far from a starburst galaxy, but our own "island universe" nevertheless contains some really massive young clusters. One of them is Westerlund 2.
R136a in the
Large Magellanic Cloud. Photo: NASA.

















In spite of the impressive mass and sparkle of Westerlund 2, it pales compared with the largest cluster in the Large Magellanic Cloud, R136a. Even at a glance, we can see that R136a is more massive than Westerlund 2. That is because R136a contains a large, spherical, compact core of brilliant stars, whereas the core of Westerlund 2 is more elongated.

Does NGC 3603 contain a spherical, compact core of brilliant stars, located in a more scattered "halo" of stars? It does indeed.
Core of NGC 3603. Credit: NASA, ESA and Wolfgang Brandner (MPIA),
Boyke Rochau (MPIA) and Andrea Stolte (University of Cologne)
Wikipedia wrote about NGC 3603:
The central star cluster is the densest concentration of very massive stars known in the galaxy.
Core of R136a. Credit: Paul Crowther, Chris Evans, VLT, ESO














Although it is very hard to compare the density of these cluster cores based on photographs, bearing in mind that R136a is about eight times farther away than NGC 3603, the best pictures of of the core of R136a don't suggest that it is a lot more compact and dense than the core of NGC 3603.

Of course, it could well be that the core of R136a is so dense that it is almost impossible to resolve it. Actually resolving it may automatically make it look less compact than it really is, at least compared with NGC 3603.

Ann
Last edited by Ann on Sun Nov 06, 2016 7:30 am, edited 1 time in total.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Boomer12k » Sun Nov 06, 2016 7:09 am

Not to be morbid... but the Westerlund 2 image looks like a lady with a raised knife about to stab something... I dare not say what...

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by heehaw » Sun Nov 06, 2016 10:59 am

Part of the beauty of the photo is the Christian-like crosses on each bright star, but these are not astronomical, but rather are produced by diffraction of light at the four supports for the secondary mirror in the reflecting telescope used to take the picture. So the "crosses" have nothing at all to do with the stars or the heavens: in fact, some telescopes have six supports (instead of four) and so you get a Mogen David instead of a cross. So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by geckzilla » Sun Nov 06, 2016 2:41 pm

heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by rstevenson » Sun Nov 06, 2016 2:59 pm

heehaw wrote:... So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
A few years back I emailed the author of my favourite image editing software -- GraphicConverter -- to ask if there was any chance of a filter being created to remove spikes from astro images. He replied, "Sorry, I have currently no idea for a good filter." And that was that. I can see the problem easily enough: the spikes are not easily selectable -- believe me, I've tried.

I just now searched online for P'Shop addons that might help, but only found ones that would add diffraction spikes, an easy thing to do. I found a page on the ESO site with advice about working with raw image files, in which they say...
Diffraction pattern: the "spider", that is the arms that support the secondary mirror of the telescope, causes a diffraction pattern that usually appears as a cross around the brightest stars. This pattern is part of the image, and must not be cleaned out. ... The diffraction patterns are part of the image, they should not be removed.
Looks like the astro imaging crowd has decided the issue once and for all, and we deviants should tug our forelocks and go away.

Rob
Last edited by rstevenson on Sun Nov 06, 2016 3:15 pm, edited 1 time in total.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Chris Peterson » Sun Nov 06, 2016 3:03 pm

rstevenson wrote:
heehaw wrote:... So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
A few years back I emailed the author of my favourite image editing software -- GraphicConverter -- to ask if there was any chance of a filter being created to remove spikes from astro images. He replied, "Sorry, I have currently no idea for a good filter." And that was that. I can see the problem easily enough: the spikes are not easily selectable -- believe me, I've tried. So, we unspike-able individuals will just have to accept that some images have spikes. For now.
Quite a few astronomical image processing packages have spike removal filters. One standard approach used by imagers who have telescopes that produce spikes (many telescopes do not) is to collect the data with the camera at two different orientations, which makes it easy to process out the spikes.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Chris Peterson » Sun Nov 06, 2016 3:06 pm

geckzilla wrote:
heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.
IRAF and other processing tools have inverse filters that can (at least partly) remove diffraction artifacts (given some information about the telescope). They do obscure useful information, but in some cases that information can still be extracted from the raw data once the effects of diffraction are compensated for. But the intent is scientific, and not generally useful when the interest is aesthetic.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by rstevenson » Sun Nov 06, 2016 3:17 pm

Chris, while you were answering, I was editing my post. I added the note of advice from ESO.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Chris Peterson » Sun Nov 06, 2016 3:48 pm

rstevenson wrote:I found a page on the ESO site with advice about working with raw image files, in which they say...
Diffraction pattern: the "spider", that is the arms that support the secondary mirror of the telescope, causes a diffraction pattern that usually appears as a cross around the brightest stars. This pattern is part of the image, and must not be cleaned out. ... The diffraction patterns are part of the image, they should not be removed.
Looks like the astro imaging crowd has decided the issue once and for all, and we deviants should tug our forelocks and go away.
Uh, no. This is simply wrong. Perhaps I'm just seeing it out of context. It is absolutely routine with professional astronomical images to utilize processing tools that compensate for diffraction artifacts. It is done with Hubble images and it is done with the images of all large ground-based telescopes.

Perhaps what they are suggesting is that they should not be processed out of the images before they are utilized scientifically.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by rstevenson » Sun Nov 06, 2016 4:16 pm

Here's the ESO page I was referring to. It seems categorical on the issue.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Chris Peterson » Sun Nov 06, 2016 4:20 pm

rstevenson wrote:Here's the ESO page I was referring to. It seems categorical on the issue.
Seems like they're talking about producing aesthetic images for outreach, not scientific processing. That's a whole different thing.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by geckzilla » Sun Nov 06, 2016 5:58 pm

Chris Peterson wrote:
rstevenson wrote:Here's the ESO page I was referring to. It seems categorical on the issue.
Seems like they're talking about producing aesthetic images for outreach, not scientific processing. That's a whole different thing.
And the aesthetic part was what I was talking about, but you responded to my post earlier with notes on scientific processing. ;)
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Ann » Sun Nov 06, 2016 7:00 pm

I find diffraction spikes useful in widefield images containing numerous galaxies, because they help us tell the stars from the galaxies. (Unless, of course, one of the galaxies hosts a brilliant quasar nucleus.)

But in today's APOD the diffraction spikes mostly clutter up the image and make the star images overlap, so that the resolution of individual stars becomes more difficult.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by geckzilla » Sun Nov 06, 2016 7:29 pm

Ann wrote:But in today's APOD the diffraction spikes mostly clutter up the image and make the star images overlap, so that the resolution of individual stars becomes more difficult.
Even without the spikes, the way the light spreads would still cause some overlap. The image would have to have either really odd processing or just be really dark overall for all those bright middle stars to not run into one another.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Visual_Astronomer » Mon Nov 07, 2016 5:23 pm

Some telescopes don't have spiders to support secondary mirrors, so diffraction spikes aren't a feature of all astro-photographs.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by starsurfer » Mon Nov 07, 2016 6:38 pm

geckzilla wrote:
heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.
Just want to ask, do you appreciate raw data?

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Pschawable » Mon Nov 07, 2016 6:53 pm

Remove the spikes? Pschawe. The spikes MAKE them stars. Signed, Me, Pschawable.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Oldironsides » Mon Nov 07, 2016 7:00 pm

Forgive me for the intrusion but I am more of a visitor than a commentor to APOD. I think I have raised the question once before but this image and the discussion about the diffraction spikes has refreshed my memory. The image explanation says it spans a distance of 17 light years but there seems to be an awful lot of stars in this cluster and while the diffraction spikes only add to the clutter I am wondering how far apart these stars are to one another? While the span, left to right may be only 17 light years, the photographic compression (foreground to background) could still be much more than that. But still these stars seem close enough to fit inside our Solar System. Any guess how far apart they are?

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by geckzilla » Mon Nov 07, 2016 7:48 pm

starsurfer wrote:
geckzilla wrote:
heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?
Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.
Just want to ask, do you appreciate raw data?
Usually. Some more than others. Some of it is so rife with defects that it hurts my eyes. Sometimes it's just breathtaking on its own; I always felt this way when I looked over one of the freshly pipelined Frontier Fields. Whether or not it's still considered "raw" after it's been through the pipeline is up to one's discretion. It's raw enough to be called raw to me in some regards.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by starsurfer » Tue Nov 08, 2016 6:28 pm

geckzilla wrote:
starsurfer wrote:
geckzilla wrote: Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.
Just want to ask, do you appreciate raw data?
Usually. Some more than others. Some of it is so rife with defects that it hurts my eyes. Sometimes it's just breathtaking on its own; I always felt this way when I looked over one of the freshly pipelined Frontier Fields. Whether or not it's still considered "raw" after it's been through the pipeline is up to one's discretion. It's raw enough to be called raw to me in some regards.
Some Hubble and ESO data is absolutely brilliant, especially some planetary nebulae! I think the brain and eyes perceive monochromatic images differently to colour?

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by geckzilla » Tue Nov 08, 2016 7:43 pm

starsurfer wrote:
geckzilla wrote:
starsurfer wrote: Just want to ask, do you appreciate raw data?
Usually. Some more than others. Some of it is so rife with defects that it hurts my eyes. Sometimes it's just breathtaking on its own; I always felt this way when I looked over one of the freshly pipelined Frontier Fields. Whether or not it's still considered "raw" after it's been through the pipeline is up to one's discretion. It's raw enough to be called raw to me in some regards.
Some Hubble and ESO data is absolutely brilliant, especially some planetary nebulae! I think the brain and eyes perceive monochromatic images differently to colour?
I don't know about that. Certainly, there are a lot of cognitive biases when perceiving colored and monochrome images which differ between individuals. It is easier to see some details in monochrome, especially darker ones, but other details, such as subtle variations in composition, are easier to see in color.
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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Ann » Wed Nov 09, 2016 6:09 am

Oldironsides wrote:Forgive me for the intrusion but I am more of a visitor than a commentor to APOD. I think I have raised the question once before but this image and the discussion about the diffraction spikes has refreshed my memory. The image explanation says it spans a distance of 17 light years but there seems to be an awful lot of stars in this cluster and while the diffraction spikes only add to the clutter I am wondering how far apart these stars are to one another? While the span, left to right may be only 17 light years, the photographic compression (foreground to background) could still be much more than that. But still these stars seem close enough to fit inside our Solar System. Any guess how far apart they are?
According to the caption, the entire image spans about 17 light-years, but the central concentration of stars is much smaller. Could the densest part of the central core be, perhaps, 3 light-years?

To estimate how close the stars are to one another, we need to know how many stars reside in a given volume. I have been unable to find an estimate of the number of stars in NGC 3603. If we include low-mass stars, however, I would think we must be talking about several thousand stars, quite possibly more than 10,000 stars for the entire cluster, and almost certainly no less than a thousand stars for the central compact core.

Would these stars fit inside our own solar system? Well, bearing in mind that the outer part of the solar system, the Oort Cloud, is supposed to extend a light-year or so from the Sun, then absolutely, there would have to be many stars in NGC 3603 within the volume of the Oort Cloud. How about the Kuiper Belt? Pluto is supposedly the largest of the Kuiper Belt objects, and its average distance to the Sun is 39.5 AU, or 39.5 times the distance from the Sun to the Earth. Yes, I think there might well be several stars within a radius of 39.5 AU in a cluster like NGC 3603, and that might include stars that are not binary or multiple stars per se, but just stars that are zipping past one another at high speeds.

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Oldironsides » Fri Nov 11, 2016 3:49 am

Ann wrote:
Oldironsides wrote:Forgive me for the intrusion but I am more of a visitor than a commentor to APOD. I think I have raised the question once before but this image and the discussion about the diffraction spikes has refreshed my memory. The image explanation says it spans a distance of 17 light years but there seems to be an awful lot of stars in this cluster and while the diffraction spikes only add to the clutter I am wondering how far apart these stars are to one another? While the span, left to right may be only 17 light years, the photographic compression (foreground to background) could still be much more than that. But still these stars seem close enough to fit inside our Solar System. Any guess how far apart they are?
According to the caption, the entire image spans about 17 light-years, but the central concentration of stars is much smaller. Could the densest part of the central core be, perhaps, 3 light-years?

To estimate how close the stars are to one another, we need to know how many stars reside in a given volume. I have been unable to find an estimate of the number of stars in NGC 3603. If we include low-mass stars, however, I would think we must be talking about several thousand stars, quite possibly more than 10,000 stars for the entire cluster, and almost certainly no less than a thousand stars for the central compact core.

Would these stars fit inside our own solar system? Well, bearing in mind that the outer part of the solar system, the Oort Cloud, is supposed to extend a light-year or so from the Sun, then absolutely, there would have to be many stars in NGC 3603 within the volume of the Oort Cloud. How about the Kuiper Belt? Pluto is supposedly the largest of the Kuiper Belt objects, and its average distance to the Sun is 39.5 AU, or 39.5 times the distance from the Sun to the Earth. Yes, I think there might well be several stars within a radius of 39.5 AU in a cluster like NGC 3603, and that might include stars that are not binary or multiple stars per se, but just stars that are zipping past one another at high speeds.

Ann
Ann,

Thank you for the detailed response. If one considers that the gravitational attraction of our Sun is strong enough to keep the outer planets in their orbits, it boggles the mind to imagine a similar attraction with several or more stars in close proximity to each other. What could keep them from tearing each other apart?

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Re: APOD: Starburst Cluster in NGC 3603 (2016 Nov 06)

Post by Ann » Fri Nov 11, 2016 5:23 am

Short answer: the gravitational attraction of each star on its own mass is much, much greater than the gravitational attraction of any star on the mass of another star.

That is, unless they come so close that they actually merge.
https://en.wikipedia.org/wiki/Blue_straggler#Formation wrote:

Several explanations have been put forth to explain the existence of blue stragglers. The simplest is that blue stragglers formed later than the rest of the stars in the cluster, but evidence for this is limited.[5] Another simple proposal is that blue stragglers are either field stars which are not actually members of the clusters to which they seem to belong, or are field stars which were captured by the cluster. This too seems unlikely, as blue stragglers often reside at the very center of the clusters to which they belong. Another theory is that blue stragglers are the result of stars that come too close to another star or similar mass object and collide.
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