DennisWisconsin is offline DennisWisconsin Post #1  March 2,2009, 9:22pm
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If you look at our group picture of the Eagle Nebulea. If there weren't stars forming in the nebulea we wouldn't see it. ???? Am I right or wrong? They write about dark matter being so mysterious but...


It's late... maybe I'm being dim...
 
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shoelace is offline shoelace Post #2  March 4,2009, 10:21am
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DennisWisconsin, wrote :

If you look at our group picture of the Eagle Nebulea. If there weren't stars forming in the nebulea we wouldn't see it. ???? Am I right or wrong? They write about dark matter being so mysterious but...


It's late... maybe I'm being dim...
How do we calculate ordinary material mass?


It's fairly straight forward in calculating the mass of luminous matter (the stars themselves).


In looking at distant galaxies you can see clouds of gas silhoutted against background stars (as you can in our own galaxy). But these clouds are constrained within the plane of the galaxy (for spirals). The mass of these particular constrained clouds of gas can be calculated.


Were there dense clouds of gas outside of these galaxies, they too would be silhoutted against the light of the stars. But they aren't, meaning they cannot be dense . This sets an upper limit on just how much mass a thin extended gas surrounding a galaxy can have. But there are other ways of determining if there is a thin gas there, such as by spectrometry. Over a distance of thousands of lightyears, even a thin gas will absorb enough of certain wavelengths of light from the emitted light of the galaxy to be measured. Calculations can be done, but you have to know a great deal about star formation, star evolution, atomic components of stars, the emitted wavelengths of the atomic components, how matter absorbs light, etc.


It's a lot of math.


And then there are the calculations as to the total mass of the universe from the moment of the Big Bang. Certain percentages of hydrogen and helium were formed then which must go into the equations of early star formation. All of the various models should be consistent with eachother if we are to have confidence in them. If you change the amount of material mass formed at the Big Bang it will subsequently affect the distribution of galaxies overall, the growth and evolution of those galaxies, the number of early supergiant stars, and as a result of the supernovas resulting from those early supergiants you will get a different compositional distribution of heavy elements in the star-forming clouds of ordinary galaxies such as our own...and solar systems would form differently.


But all of this is still a work in progress. We know very little about solar systems. We know of some 400 plus extra-solar planets now (we didn't know of any when I was young). Each piece of the puzzle discovered helps refine the model.


Dark Matter presumably shows up as missing mass in galaxies. Whole galaxy clusters orbit about eacheother at velocities that cannot be explained by visible matter alone. I am presuming that were this missing mass existent in the form of, say, hydrogen, that it would be thick enough to observe by current means (it would absorb a LOT of light). This is why some scientists suggest dark matter may be composed of exotic particles, or neutrinos...particles which do not interact very much with common matter (photons), and thus would be hard to detect by conventional means--they would not silhoutte very well against the background light.


The mass is predicted to be there by gravitational equations. But apparently spectrometry doesn't reveal enough free floating hydrogen outside of the galaxies themselves, which is where the missing mass is thought to be.


The question, then, is how do you calculate the visible (gas clouds and stars) matter of a galaxy?
 
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notamaninpower is offline notamaninpower Post #3  March 4,2009, 12:31pm
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Is the Eagle Nebula aka "The Fingers Of Creation"??
 
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shoelace is offline shoelace Post #4  March 4,2009, 6:26pm
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notamaninpower,515452 wrote :

Is the Eagle Nebula aka "The Fingers Of Creation"??
I haven't heard that phrase used. But, technically, I would doubt it refers to the Eagle nebula, as the nebula gets its name because it looks like an eagle. The particular formation in the photograph--used for this group--is an extreme closeup made by the Hubble of a small region within the Eagle nebula (the heart of the nubula). The photo does have the appearance of "fingers," and so the phrase "The Fingers of Creation." It must refer to this particular formation within the Eagle, but not to the Eagle itself.


Within these fingers, stars are forming (thus, fingers of creation). The fingers themselves, made of diffuse gases, are formed by stellar winds blowing the gases away leaving behind these thicker segments extending into the wind. Upon closer inspection you would be able to see even smaller fingers, or splinters, extending off of the fingers where proto-stellar globules are directly butting up against the stellar wind. And some distance from the fingers you would see black spherules of proto-stellar material which has had most of the surrounding gases blown away by the wind (the fingers used to extend out to those spherules, engulfing them at one time, but the wind blew the gases away to their present "finger" location).


Eventually the fingers will be blown away completely by the stellar wind of stars which have already formed in the nebula.
 
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notamaninpower is offline notamaninpower Post #5  March 5,2009, 12:08pm
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shoelace,515978 wrote :


notamaninpower,515452 wrote :


Is the Eagle Nebula aka "The Fingers Of Creation"??


I haven't heard that phrase used. But, technically, I would doubt it refers to the Eagle nebula, as the nebula gets its name because it looks like an eagle. The particular formation in the photograph--used for this group--is an extreme closeup made by the Hubble of a small region within the Eagle nebula (the heart of the nubula). The photo does have the appearance of "fingers," and so the phrase "The Fingers of Creation." It must refer to this particular formation within the Eagle, but not to the Eagle itself.


Within these fingers, stars are forming (thus, fingers of creation). The fingers themselves, made of diffuse gases, are formed by stellar winds blowing the gases away leaving behind these thicker segments extending into the wind. Upon closer inspection you would be able to see even smaller fingers, or splinters, extending off of the fingers where proto-stellar globules are directly butting up against the stellar wind. And some distance from the fingers you would see black spherules of proto-stellar material which has had most of the surrounding gases blown away by the wind (the fingers used to extend out to those spherules, engulfing them at one time, but the wind blew the gases away to their present "finger" location).


Eventually the fingers will be blown away completely by the stellar wind of stars which have already formed in the nebula.


Thanks. GREAT explanation, but I was referring to the pic of this section/formation of the Eagle nebula. (Yes,I know I should have specified only the formation in the group pic.)


"Eventually the fingers will be blown away completely by the stellar wind of stars which have already formed in the nebula."


Have astrophysicists estimated how long until this occurs??
 
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shoelace is offline shoelace Post #6  March 6,2009, 2:46pm
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notamaninpower,516850 wrote :

shoelace,515978 wrote :


notamaninpower,515452 wrote :


Is the Eagle Nebula aka "The Fingers Of Creation"??


I haven't heard that phrase used. But, technically, I would doubt it refers to the Eagle nebula, as the nebula gets its name because it looks like an eagle. The particular formation in the photograph--used for this group--is an extreme closeup made by the Hubble of a small region within the Eagle nebula (the heart of the nubula). The photo does have the appearance of "fingers," and so the phrase "The Fingers of Creation." It must refer to this particular formation within the Eagle, but not to the Eagle itself.


Within these fingers, stars are forming (thus, fingers of creation). The fingers themselves, made of diffuse gases, are formed by stellar winds blowing the gases away leaving behind these thicker segments extending into the wind. Upon closer inspection you would be able to see even smaller fingers, or splinters, extending off of the fingers where proto-stellar globules are directly butting up against the stellar wind. And some distance from the fingers you would see black spherules of proto-stellar material which has had most of the surrounding gases blown away by the wind (the fingers used to extend out to those spherules, engulfing them at one time, but the wind blew the gases away to their present "finger" location).


Eventually the fingers will be blown away completely by the stellar wind of stars which have already formed in the nebula.


Thanks. GREAT explanation, but I was referring to the pic of this section/formation of the Eagle nebula. (Yes,I know I should have specified only the formation in the group pic.)


"Eventually the fingers will be blown away completely by the stellar wind of stars which have already formed in the nebula."


Have astrophysicists estimated how long until this occurs??
That would be an excellent elementary physics problem for a grad student.


The force of the original stellar wind would weaken over time as the roughly spherical shell of wind (protons?) expanded. But new stars are forming within the fingers. These will eventually "ignite" and blow a wind of protons of their own. The wind from these new stars could create new fingers of their own out of denser regions embedded within the larger nebula.


It would be wonderful to see a time-lapse film of such a birthing area.


If I have time, maybe I'll try to dig up some information on how long it would take for the fingers to dissipate.
 
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shoelace is offline shoelace Post #7  March 8,2009, 10:43am
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Apparently, scientists have dubbed the Fingers of Creation as the Pillars of Creation . You can get a little information about them by looking up Eagle Nebula in wikipedia.


The Eagle is 7000 lightyears from us.


According to a NASA press release referenced on widipedia, these Pillars may already be blown away by a supernova which has exploded nearby. The pillars would have been destroyed 6000 years ago from the blast, but light from that event won't reach us for another 1000 years.


The oldest stars of the Eagle nebula are around 5.5 million years old. The birth of these first stars marks when the nebula would have first become visible. The nebula shines due to the excitation of its gaseous atoms by the ultraviolet light radiated from the newborn stars. It is hypothesized that a spate of star formation took place there 1 million years ago, but has since slowed.


I couldn't find an exact measurement of the length of the pillars, but I did find one for another similar finger within the nebula, and that finger measures between 9 and 10 lightyears long.


Lets say the Pillars are roughly 9 lightyears long, and lets say the stellar wind from the hot young stars blows at a fast 2000 km/s (it's an educated guess). If you were flying in a sail propelled spacecraft, blown by this wind, it would take you over 16,000 years to fly past these fingers.


But the pillars are not likely to be blown away in as short a time as this. The plasma particles of the wind would have to impact with the particles of the Pillars, slowly accelerating them to wind speed through multiple impacts. The outside of the pillar would have to be eroded before the inner regions could be reached. If you thought of it as stripping off layers, like peeling an onion, with it taking 16,000 years per layer, by estimating the number of layers you must remove you would then have the time it would take to dissipate the Pillars. Ten layers would require 160 thousand years, one hundred layers would be 1.6 million years . It would take far longer than 16,000 years, either way, for the pillars to be blown away in this manner.


Consider another estimation: measure the distance between the wind-emitting star cluster that is lighting the nebula and the Pillars. This is a measure of how much gas has already been blown away in 5.5 million years (admittedly, the more stars born the greater the force of the stellar wind, and the faster the erosion). In simply looking at a photo of the Eagle I would estimate the Pillars are 1/3 this distance. One third of 5.5 million is 1.8 million years . But, of course, a real answer would require real physics calculations. (I am leaving out other factors, such as the density of the Pillars which caused them to be left behind in the first place while the rest of the gases were blown past.)


These are just my guesses.


Another question is, how long did it take the supernova to blow away the Pillars? (At this moment, it is assumed the Pillars no longer exist.) The speed of the gases blown from the supernova would be significantly higher than the speed of the stellar wind. Additionally, the supernova blast might have hit at a right angle to the long dimension of the Pillars. The short dimension appears to be about 1 lightyear wide.


I have no idea how fast a supernova blast expands, so I can't make a guess. But a thousand years from now we may be able to capture a time lapse video of this destruction.
 
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DennisWisconsin is offline DennisWisconsin Post #8  March 8,2009, 11:04am
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Incredible information shoelace! Thank you!
 
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shoelace is offline shoelace Post #9  March 8,2009, 11:45am
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I picked this up from Wikipedia: a supernova can expell material at up to 1/10 the speed of light. Were this the case for the Eagle nebula supernova, the recognizable shape of the Pillars could be completely disrupted in as little as 10 years. Film at 11 (1000 years hence).
 
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DennisWisconsin is offline DennisWisconsin Post #10  March 8,2009, 2:43pm
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shoelace,521014 wrote :

I picked this up from Wikipedia: a supernova can expell material at up to 1/10 the speed of light. Were this the case for the Eagle nebula supernova, the recognizable shape of the Pillars could be completely disrupted in as little as 10 years. Film at 11 (1000 years hence).
The Eagle Nebula is located in the next inner ring (Sagittarius arm) of the Milky Way Galaxy. It's linear dimensions are 70 x 55 light years in its entirety and it is 7,000 light years from Earth. This is no small object...
 
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