APOD: Star Factory Messier 17 (2014 May 27)

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APOD: Star Factory Messier 17 (2014 May 27)

Postby APOD Robot » Tue May 27, 2014 4:06 am

Image Star Factory Messier 17

Explanation: What's happening at the center of this nebula? Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this degree wide field of view spans almost 100 light-years. The sharp, composite, color image utilizing data from space and ground based telescopes, follows faint details of the region's gas and dust clouds against a backdrop of central Milky Way stars. Stellar winds and energetic light from hot, massive stars formed from M17's stock of cosmic gas and dust have slowly carved away at the remaining interstellar material producing the cavernous appearance and undulating shapes. M17 is also known as the Omega Nebula or the Swan Nebula.

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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Ann » Tue May 27, 2014 4:12 am

This is a very fine picture of a most interesting site of star formation in the Milky Way. I believe that there are at least seven newborn O-type stars in the nebula, hidden from (optical) view by thick clouds. The massive star cluster is behind the clouds far to the right in the picture, I think.

I've read some place that the hot newborn stars produce a terrific stellar wind that was described by an astronomer as a "champagne flow". Pwerhaps the champagne flow can be seen as the bluish part of the nebula.

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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Boomer12k » Tue May 27, 2014 9:23 am

Wow...layers of filigree....awesome image.

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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby neufer » Tue May 27, 2014 1:53 pm

APOD Robot wrote:
Explanation: Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this degree wide field of view spans almost 100 light-years.

http://en.wikipedia.org/wiki/Messier_17 wrote:
<<The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years (~10 arcmins) in diameter.
The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter.>>
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Psnarf » Tue May 27, 2014 2:08 pm

Approximately how many stars are generating the stellar winds and radiation that energize the visible nebula? 44-Trillion miles is quite a distance for energized particles to travel in order to knock electrons off of some interstellar clouds. (assuming a 7.5 light-year radius)

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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 2:33 pm

neufer wrote:
APOD Robot wrote:
Explanation: Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this degree wide field of view spans almost 100 light-years.

http://en.wikipedia.org/wiki/Messier_17 wrote:
<<The Omega Nebula is between 5,000 and 6,000 light-years from Earth and it spans some 15 light-years (~10 arcmins) in diameter.
The cloud of interstellar matter of which this nebula is a part is roughly 40 light-years in diameter.>>


It must be very challenging to keep up to date with every astronomical fact and figure, but that's why fact checkers, proofreaders and editors are needed.

So in this case, the assumed distance has remained about the same but the new thinking is that the nebula is 60% smaller? That calls for some further explanation.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Beyond » Tue May 27, 2014 4:20 pm

One word, Bruce... inflation. It's everywhere!!
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 5:05 pm

Beyond wrote:One word, Bruce... inflation. It's everywhere!!

But, apparently, this nuebula nebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.
Last edited by BDanielMayfield on Tue May 27, 2014 7:42 pm, edited 1 time in total.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby neufer » Tue May 27, 2014 5:26 pm

Psnarf wrote:
Approximately how many stars are generating the stellar winds and radiation that energize the visible nebula? 44-Trillion miles is quite a distance for energized particles to travel in order to knock electrons off of some interstellar clouds. (assuming a 7.5 light-year radius)
http://en.wikipedia.org/wiki/Messier_17 wrote:
<<An open cluster of 35 stars lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however the actual number of stars in the nebula is much higher - up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O, plus >1000 stars in formation on its outer regions. It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on. It's also one of the youngest clusters known, with an age of just 1 million years.>>
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Beyond » Tue May 27, 2014 5:33 pm

BDanielMayfield wrote:
Beyond wrote:One word, Bruce... inflation. It's everywhere!!

But, apparently, this nuebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.

oops!! Forgetted about the Wikipedia entry, which seems to be the smallest one. But since we should go by the general consensus, (3-100lyrs, 1-50lyrs and 1-15lyrs) then it is 100lyrs across. Right?
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 5:36 pm

BDanielMayfield wrote:
Beyond wrote:One word, Bruce... inflation. It's everywhere!!

But, apparently, this nebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.

To be clear, I don't mean that literally, I was just joking with Beyond. The nebula's true size wouldn't have changed all that much, but reports about it's size have. Or, could nuefer's point be that old errors about its size keep getting re-copied?
Last edited by BDanielMayfield on Tue May 27, 2014 7:43 pm, edited 1 time in total.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Ann » Tue May 27, 2014 5:44 pm

BDanielMayfield wrote:
Beyond wrote:One word, Bruce... inflation. It's everywhere!!

But, apparently, this nuebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.


When I checked the assumed, spectral-class derived distances to hot blue stars in Sky Catalogue 2000.0 and compared them with their distances as measured by Hipparcos, I found that the brightness of blue stars based on their spectral classes had been systematically overstimated by Sky Catalogue 2000.0. Oh, there were a few exceptions, of course, some monstrously bright blue stars. By and large, however, the blue stars turned out to be fainter than astronomers had expected. A good example of a young and very blue O star that is fainter than astronomers would have thought is S Monocerotis, also known as S Mon or 15 Mon.

I'm going to guess that we are seeing a somewhat similar effect when it comes to the Swan Nebula, or M17. Astronomers found a large number of O stars in Messier 17, and so they may have just assumed that the nebula was titanic. I'm going to guess, by the way, that the very young O stars of M17 are fainter than astronomers first thought. Intrinsically brighter O-type stars might have called for a larger nebula, but if the O-type stars turned out to be fainter than expected, the nebula might have "shrunk" as well.

Why are O-stars fainter than expected, by the way? I'm going to guess here. I think it is the very young O-stars that are faint, and that very young stars simply "do less fusion" than older stars, and so generate less energy. The reason might possibly be that a smaller part of the star is involved in doing fusion in very young stars. As the star ages, more and more of it becomes involved in doing fusion, as the fusion zone moves outward in the star, sort of "covering more" of the existing material there. Also, I think that young main sequence stars are typically smaller in size than somewhat older main sequence stars, and unexpectedly small stars are typically going to be unexpectedly faint. As an aside, I suspect that most (and just possibly all) unexpectedly faint stars of any spectral class are unexpectedly small in size.

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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 5:58 pm

neufer wrote:
Psnarf wrote:
Approximately how many stars are generating the stellar winds and radiation that energize the visible nebula? 44-Trillion miles is quite a distance for energized particles to travel in order to knock electrons off of some interstellar clouds. (assuming a 7.5 light-year radius)
http://en.wikipedia.org/wiki/Messier_17 wrote:
<<An open cluster of 35 stars lies embedded in the nebulosity and causes the gases of the nebula to shine due to radiation from these hot, young stars; however the actual number of stars in the nebula is much higher - up to 800, 100 of spectral type earlier than B9, and 9 of spectral type O, plus >1000 stars in formation on its outer regions. It is considered one of the brightest and most massive star-forming regions of our galaxy. Its local geometry is similar to the Orion Nebula except that it is viewed edge-on rather than face-on. It's also one of the youngest clusters known, with an age of just 1 million years.>>

I was going to answer Psnarf's question with the same quotation Art. It may irk you to see me state this, but you and I do think in similar ways, but my brain has less stored data and opperates at a slower baud rate. :wink:
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby neufer » Tue May 27, 2014 6:42 pm

BDanielMayfield wrote:
To be clear, I don't mean that literally, I was just joking with Beyond. The nuebula's true size wouldn't have changed all that much, but reports about it's size have. Or, could nuefer's point be that old errors about its size keep getting re-copied?

Specifics about the size of an old frame [~ 1º ~ 100 ly] keep getting re-copied even though the pictures themselves change.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 7:00 pm

neufer wrote:
BDanielMayfield wrote:
To be clear, I don't mean that literally, I was just joking with Beyond. The nuebula's true size wouldn't have changed all that much, but reports about it's size have. Or, could nuefer's point be that old errors about its size keep getting re-copied?

Specifics about the size of an old frame [~ 1º ~ 100 ly] keep getting re-copied even though the pictures themselves change.

Something like that was what I (eventually) thought was your main point. Thanks for the clarification.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 7:10 pm

Ann wrote:
BDanielMayfield wrote:
Beyond wrote:One word, Bruce... inflation. It's everywhere!!

But, apparently, this nuebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.


When I checked the assumed, spectral-class derived distances to hot blue stars in Sky Catalogue 2000.0 and compared them with their distances as measured by Hipparcos, I found that the brightness of blue stars based on their spectral classes had been systematically overstimated by Sky Catalogue 2000.0. Oh, there were a few exceptions, of course, some monstrously bright blue stars. By and large, however, the blue stars turned out to be fainter than astronomers had expected. A good example of a young and very blue O star that is fainter than astronomers would have thought is S Monocerotis, also known as S Mon or 15 Mon.

I'm going to guess that we are seeing a somewhat similar effect when it comes to the Swan Nebula, or M17. Astronomers found a large number of O stars in Messier 17, and so they may have just assumed that the nebula was titanic. I'm going to guess, by the way, that the very young O stars of M17 are fainter than astronomers first thought. Intrinsically brighter O-type stars might have called for a larger nebula, but if the O-type stars turned out to be fainter than expected, the nebula might have "shrunk" as well.

Why are O-stars fainter than expected, by the way? I'm going to guess here. I think it is the very young O-stars that are faint, and that very young stars simply "do less fusion" than older stars, and so generate less energy. The reason might possibly be that a smaller part of the star is involved in doing fusion in very young stars. As the star ages, more and more of it becomes involved in doing fusion, as the fusion zone moves outward in the star, sort of "covering more" of the existing material there. Also, I think that young main sequence stars are typically smaller in size than somewhat older main sequence stars, and unexpectedly small stars are typically going to be unexpectedly faint. As an aside, I suspect that most (and just possibly all) unexpectedly faint stars of any spectral class are unexpectedly small in size.

Ann


No real shrinkage has occurred though, since this has been an Artfully contrived tempest in an APOT APOD. :lol2:
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Tue May 27, 2014 8:24 pm

BDanielMayfield wrote:It must be very challenging to keep up to date with every astronomical fact and figure, but that's why fact checkers, [spellcheckers], proofreaders and editors are needed.


When the data from the Gaia mission comes in with its much more accurate distances to about a million stars there will need to be a great deal of revisions, but it will be great to actually know (within much smaller uncertainties) the distances, actual brightness, sizes, masses, etc. of so much of our galaxy and even beyond.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Beyond » Tue May 27, 2014 9:04 pm

Well, no. Much of my brightness, etc. is still very well hidden.
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby BDanielMayfield » Wed May 28, 2014 3:39 am

BDanielMayfield wrote:
Ann wrote:
BDanielMayfield wrote:But, apparently, this nebula has experienced deflation, since it has gotten smaller. Something just dosen't add up here.


When I checked the assumed, spectral-class derived distances to hot blue stars in Sky Catalogue 2000.0 and compared them with their distances as measured by Hipparcos, I found that the brightness of blue stars based on their spectral classes had been systematically overstimated by Sky Catalogue 2000.0. Oh, there were a few exceptions, of course, some monstrously bright blue stars. By and large, however, the blue stars turned out to be fainter than astronomers had expected. A good example of a young and very blue O star that is fainter than astronomers would have thought is S Monocerotis, also known as S Mon or 15 Mon.

I'm going to guess that we are seeing a somewhat similar effect when it comes to the Swan Nebula, or M17. Astronomers found a large number of O stars in Messier 17, and so they may have just assumed that the nebula was titanic. I'm going to guess, by the way, that the very young O stars of M17 are fainter than astronomers first thought. Intrinsically brighter O-type stars might have called for a larger nebula, but if the O-type stars turned out to be fainter than expected, the nebula might have "shrunk" as well.

Why are O-stars fainter than expected, by the way? I'm going to guess here. I think it is the very young O-stars that are faint, and that very young stars simply "do less fusion" than older stars, and so generate less energy. The reason might possibly be that a smaller part of the star is involved in doing fusion in very young stars. As the star ages, more and more of it becomes involved in doing fusion, as the fusion zone moves outward in the star, sort of "covering more" of the existing material there. Also, I think that young main sequence stars are typically smaller in size than somewhat older main sequence stars, and unexpectedly small stars are typically going to be unexpectedly faint. As an aside, I suspect that most (and just possibly all) unexpectedly faint stars of any spectral class are unexpectedly small in size.

Ann


No real shrinkage has occurred though, since this has been an Artfully contrived tempest in an APOT APOD. :lol2:


Ann, sorry if my kidding deflated your carefully thought out and well stated argument. Stars do shrink in size as they first enter the main sequence, including the most massive O-stars. Then they get puffed up as they age, like some people. :ssmile:
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Re: APOD: Star Factory Messier 17 (2014 May 27)

Postby Ann » Wed May 28, 2014 4:03 am

No worries, Bruce. Your reply to Art was quite funny.

As for puffing up as you age... yes, that has been known to happen!

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