Beautiful as always! Now, this galaxy is said to be "about 170,000 light-years across." What do I see in the picture? First, a strong concentration of white light around the nucleus; a little farther out, a dense swirl of stars and dust with a fairly tight vortex pattern; and much farther - towards the edges of the picture (especially on the viwer's left) - things that seem to be enormous gassy clusters surrounded by black space, but that also seem to line up as distant extensions of the galaxy's spiral pattern.
My question is, what do they consider to be the boundaries of a galaxy?
M101 2-march-2006
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harry
- G'day G'day G'day G'day
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Hello Axel
Re:http://antwrp.gsfc.nasa.gov/apod/ap060302.html
The length is determined by the extreme observable edges.
Re:http://antwrp.gsfc.nasa.gov/apod/ap060302.html
The length is determined by the extreme observable edges.
Harry : Smile and live another day.
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greatergood
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This probably sounds sophomoric too but... I'm still in the dark. What defines the observable edges? (See my original post.)harry wrote:Hello Axel
Re:http://antwrp.gsfc.nasa.gov/apod/ap060302.html
The length is determined by the extreme observable edges.
Boundaries and Spin
Axel,
Not to be too philosophical, but, the edge is a definitionary sort of thing. It is as we define it to be. My guess at the definition is;
A galaxy's boundary is where its gravity tapers off to such an extent that material in the interstellar medium is unsure of what direction to go in.
Under this idea, the long spiral arms in the photo that have gas clouds condensing to form bright star birthing nurserys, and are quite a ways away from the contiguous galactic homogenious area; those island bright star areas are a part of the galaxy, as well as the gas and dust that is not emitting visible light, and probably difusely parsed all over the general area.
I would think a galaxy's bailiwick is as far as its gravity can muster contributions, even tho there is no visible material in some of those areas.
And to include any outlying island clouds within a diameter from the central area, or maybe more.
After all, to whom would those outrigger star clouds be attracted to?
Thusly possession is still 9/10's of the Law of the Universe !
and Gravity be the Judge.
Greatergood,
Galaxies spin because, when the material that drew together which made the galaxy, it was not all going directly toward the compromise center of todays galaxy, so it began in its various fashions, to orbit the agreed upon center of the galaxy.
Any breezes in the primordial hydrogen and dust clouds, would translate into a path that will end up in an orbit around the compromise center of the galactic mass. Any vector will end up turning under gravity and become an orbit, thus the galactic rotation.
Otherwise, under perfect uniform conditions of all material drawing directly toward the center of the new galaxy, it would become a black hole very quickly, as everything would fall straight in.
Any direction other than straight in will end up in a spin of some sort, and by the gravitational interaction between the material in the mean time, it will again compromise into the spiral arms etc that the galaxy shows.
Now an elliptical galaxy is one where the gas cloud was exceptionally still during its clumping into stars. So the stars formed before the galaxy ever started to rotate, as everything was stillness; then the stars began to move as their gravity began to pull slowly on each other unevenly, and we end up with the stars moving around a compromise center of mass, but because there is so much space between the stars they hardly ever collide, they swerve around each other like a in a do-se-do square dance.
Also, the stars condensed and began to shine before the entire cloud had time to condense into a black hole; and then the stars began to dance before they were able to fall into the black hole either.
In this way spacetime, being so large; it kept the matter from falling into a black hole too soon, and thusly the Universe Lives !
Not to be too philosophical, but, the edge is a definitionary sort of thing. It is as we define it to be. My guess at the definition is;
A galaxy's boundary is where its gravity tapers off to such an extent that material in the interstellar medium is unsure of what direction to go in.
Under this idea, the long spiral arms in the photo that have gas clouds condensing to form bright star birthing nurserys, and are quite a ways away from the contiguous galactic homogenious area; those island bright star areas are a part of the galaxy, as well as the gas and dust that is not emitting visible light, and probably difusely parsed all over the general area.
I would think a galaxy's bailiwick is as far as its gravity can muster contributions, even tho there is no visible material in some of those areas.
And to include any outlying island clouds within a diameter from the central area, or maybe more.
After all, to whom would those outrigger star clouds be attracted to?
Thusly possession is still 9/10's of the Law of the Universe !
and Gravity be the Judge.
Greatergood,
Galaxies spin because, when the material that drew together which made the galaxy, it was not all going directly toward the compromise center of todays galaxy, so it began in its various fashions, to orbit the agreed upon center of the galaxy.
Any breezes in the primordial hydrogen and dust clouds, would translate into a path that will end up in an orbit around the compromise center of the galactic mass. Any vector will end up turning under gravity and become an orbit, thus the galactic rotation.
Otherwise, under perfect uniform conditions of all material drawing directly toward the center of the new galaxy, it would become a black hole very quickly, as everything would fall straight in.
Any direction other than straight in will end up in a spin of some sort, and by the gravitational interaction between the material in the mean time, it will again compromise into the spiral arms etc that the galaxy shows.
Now an elliptical galaxy is one where the gas cloud was exceptionally still during its clumping into stars. So the stars formed before the galaxy ever started to rotate, as everything was stillness; then the stars began to move as their gravity began to pull slowly on each other unevenly, and we end up with the stars moving around a compromise center of mass, but because there is so much space between the stars they hardly ever collide, they swerve around each other like a in a do-se-do square dance.
Also, the stars condensed and began to shine before the entire cloud had time to condense into a black hole; and then the stars began to dance before they were able to fall into the black hole either.
In this way spacetime, being so large; it kept the matter from falling into a black hole too soon, and thusly the Universe Lives !
I would propose a slightly different view of why some galaxies spin.
As seems to be the order of things in our universe, single bodies rotate. (stars rotate, planets rotate, moons rotate, even most asteroids and comets rotate). Rotation seems to be the order of most singular bodies in space. To that end, Black holes should also rotate.
That rotation will cause a warping in the fabric of space that surrounds the body in question creating a shape with the strongest part of the gravity well at the center of the body and which gradually lessens as you move away. The rotation of the body and the subsequent warping of space tends to pull the orbiting bodies around the equatorial plane of the main or closest gravity source.
The Sun orbits around the galactic equatorial plane because the super-massive central black hole is spinning in one direction, tugging against space in a that certain direction, Neptune orbits the sun around the solar equatorial plane in the direction of the solar rotation but its moons orbit around the planetary equatorial plane in the direction of the planetary rotation.
Rotation of a central overwhelming gravity source will tend to pull its orbiting bodies in one direction around its equatorial plane with the closest source taking precedence.
If there is no ruling central gravity source then the objects will orbit around a central point but not in any equatorial plane (no central spin). They will still try to maintain equatorial type of rotation though as unanchored galaxies are still elliptical and not spherical.
As seems to be the order of things in our universe, single bodies rotate. (stars rotate, planets rotate, moons rotate, even most asteroids and comets rotate). Rotation seems to be the order of most singular bodies in space. To that end, Black holes should also rotate.
That rotation will cause a warping in the fabric of space that surrounds the body in question creating a shape with the strongest part of the gravity well at the center of the body and which gradually lessens as you move away. The rotation of the body and the subsequent warping of space tends to pull the orbiting bodies around the equatorial plane of the main or closest gravity source.
The Sun orbits around the galactic equatorial plane because the super-massive central black hole is spinning in one direction, tugging against space in a that certain direction, Neptune orbits the sun around the solar equatorial plane in the direction of the solar rotation but its moons orbit around the planetary equatorial plane in the direction of the planetary rotation.
Rotation of a central overwhelming gravity source will tend to pull its orbiting bodies in one direction around its equatorial plane with the closest source taking precedence.
If there is no ruling central gravity source then the objects will orbit around a central point but not in any equatorial plane (no central spin). They will still try to maintain equatorial type of rotation though as unanchored galaxies are still elliptical and not spherical.
Okay, my brain shall assume that galaxies extend to where their gravitational influence is in equilibrium with external gravitational influences. That would make an interesting 3-dimensional map of galactic "territories", filled with a spongy net composed of an uninterrupted gravitational boundary sheet. Would such a boundary be called a barypause?
BTW, a recurring thought-experiment in my daydreams goes something like this: What would a universe be like where massive bodies did not spin? (Quantum entities excluded.) But that's for another thread...
A test of that would be that bodies with retrograde spins, such as Venus, would tend to slow down with time.BMAONE23 wrote:I would propose a slightly different view of why some galaxies spin.
[ ... ]
Rotation of a central overwhelming gravity source will tend to pull its orbiting bodies in one direction around its equatorial plane with the closest source taking precedence.
BTW, a recurring thought-experiment in my daydreams goes something like this: What would a universe be like where massive bodies did not spin? (Quantum entities excluded.) But that's for another thread...
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greatergood
- Ensign
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- Joined: Sun Sep 04, 2005 3:35 am
These are all good thoughts, but I'm afraid I'm still not satisfied. As far as I can tell there are 3 theories for celestial rotational motion throughout the universe:
1) Galaxies are closed systems that began to spin on their own. This defies the laws of physics. Conservation of energy says closed systems don't spontaneously develop rotational motion on their own (unless the center starts spinning in one direction and the edges spin in an opposite direction at the expense of an internal reaction currently not understood). Although there will develop internal small localized spins here and there as matter condenses and gravitational forces form within the system, but as a closed whole system, a non-spinning system will remain rotationally stagnant regardless what spins develop in small localized areas of the system.
2) Galaxies are composed of matter that was already spinning at their existing centripital velocities since the big bang, which is contrary to big bang theory. The centripetal velocities of the outlying stars relative to the galactic center are huge enough that they cannot easily be explained by averaging the random movements of condensing matter. Besides, "maximal symmetry" of the Big Bang theory suggests that the expansion of matter was consistent throughout the universe, suggesting that such large pre-existing centripital velocities of clumpy matter spinning about a future galactic center is highly unlikely, let alone commonplace.
3) Galaxies are open systems that spin due to outside forces. Unfortunately, that's not what we observe. The most beautiful spiral galaxies appear to be completely isolated in the vacuum of space seperated by other galaxies with incomprehensible distances. In fact, where galaxies are close to each other they don't cause spin - rather they rip each other apart. I do like the idea of a spinning black hole in the middle, but what cased the black hole to spin in the first place? So that doesn't solve the problem either.
So what's causing celestial rotational motion at such high velocities?
It possible that the galactic spinning motions that we observe are similar to something like dot-products of the spin of the whole universe (analogous to draining water that spins because of the earth's rotation)? If so, could the planets that spin in a solar system also be a similar product of the spin of a galaxy? Of course this all begs the question of "how can a universe spin", but I'm guessing we have to really think outside the box to answer that question.
I think it's entirely possible that galactic spin involves some galactic-level physics that we don't yet understand, making possible the first two seemingly impossible solutions mentioned above. We obviously don't know why there's such things as stable star clusters - and maybe we ought to also admit that we also don't know why galaxies spin.
It seems like spin is very very important, and I'm not just talking about the slight spin that might result from the average of initial trajectories of clumpy matter after the Big Bang. I'm talking about mind blowingly fast centripital movement in galaxies and solar systems as being the most important component to a healthy universe, especially a universe capable of supporting life. Sadly, I've never been satisfied with any explanations so far as to why such high centripital velocities are so prevalent. It seems like it could hold one of the keys to understanding galactic physics.
1) Galaxies are closed systems that began to spin on their own. This defies the laws of physics. Conservation of energy says closed systems don't spontaneously develop rotational motion on their own (unless the center starts spinning in one direction and the edges spin in an opposite direction at the expense of an internal reaction currently not understood). Although there will develop internal small localized spins here and there as matter condenses and gravitational forces form within the system, but as a closed whole system, a non-spinning system will remain rotationally stagnant regardless what spins develop in small localized areas of the system.
2) Galaxies are composed of matter that was already spinning at their existing centripital velocities since the big bang, which is contrary to big bang theory. The centripetal velocities of the outlying stars relative to the galactic center are huge enough that they cannot easily be explained by averaging the random movements of condensing matter. Besides, "maximal symmetry" of the Big Bang theory suggests that the expansion of matter was consistent throughout the universe, suggesting that such large pre-existing centripital velocities of clumpy matter spinning about a future galactic center is highly unlikely, let alone commonplace.
3) Galaxies are open systems that spin due to outside forces. Unfortunately, that's not what we observe. The most beautiful spiral galaxies appear to be completely isolated in the vacuum of space seperated by other galaxies with incomprehensible distances. In fact, where galaxies are close to each other they don't cause spin - rather they rip each other apart. I do like the idea of a spinning black hole in the middle, but what cased the black hole to spin in the first place? So that doesn't solve the problem either.
So what's causing celestial rotational motion at such high velocities?
It possible that the galactic spinning motions that we observe are similar to something like dot-products of the spin of the whole universe (analogous to draining water that spins because of the earth's rotation)? If so, could the planets that spin in a solar system also be a similar product of the spin of a galaxy? Of course this all begs the question of "how can a universe spin", but I'm guessing we have to really think outside the box to answer that question.
I think it's entirely possible that galactic spin involves some galactic-level physics that we don't yet understand, making possible the first two seemingly impossible solutions mentioned above. We obviously don't know why there's such things as stable star clusters - and maybe we ought to also admit that we also don't know why galaxies spin.
It seems like spin is very very important, and I'm not just talking about the slight spin that might result from the average of initial trajectories of clumpy matter after the Big Bang. I'm talking about mind blowingly fast centripital movement in galaxies and solar systems as being the most important component to a healthy universe, especially a universe capable of supporting life. Sadly, I've never been satisfied with any explanations so far as to why such high centripital velocities are so prevalent. It seems like it could hold one of the keys to understanding galactic physics.
=================
PI-Rn't-Square. They're round.
PI-Rn't-Square. They're round.
Perhaps large round bodies need the spinning mechanism to become round. this would dictate that in the process of becoming round, a large lopsided object will require a spinning motion in order to redistribute its matter to become spherical in shape. Even the motion of large scale movement could cause a spin as the specific gravity of one group of particles acts upon another through movement.
Another possibility is inertia. As one body is impacted by another both are imparted with a rotational spin.
Given that these bodies are spinning in a vaccuum, there is little appreciable energy lost during the course of several life times. They will appear to spin forever, relative to our life spans.
The point is, regardless of how the spin starts, all round bodies and most if not all other bodies rotate. I know of no rocks in space that do not have rotation. (dust, like dark, is another matter) I don't know if the particles in the Saturnian ring system tumble independantly of each other.
Perhaps, in our early solar system, the sun condensed in its gas cloud (the remnant of some long ago super-nova). The heavier particles close to the new star were pulled in, imparting their energy into causing and then revving up the stellar rotation. As the gravity source began to rotate, it began to warp the fabric of space around it, pulling on the particles surrounding it and causing them to rotate. This rotation then in turn assured that most particles in the solar equitorial plane began to rotate in the same direction also ensuring that any further heavy particle bombardment of the young star would happen in the same direction of rotation. This might also serve to cause banding within the dust/debris disk there by causing ultimate planetary formation to occur.
This scenerio works weather on a planetary (Earth, Moon) level, Solar system level, or galactic level.
[/i]
Another possibility is inertia. As one body is impacted by another both are imparted with a rotational spin.
Given that these bodies are spinning in a vaccuum, there is little appreciable energy lost during the course of several life times. They will appear to spin forever, relative to our life spans.
The point is, regardless of how the spin starts, all round bodies and most if not all other bodies rotate. I know of no rocks in space that do not have rotation. (dust, like dark, is another matter) I don't know if the particles in the Saturnian ring system tumble independantly of each other.
Perhaps, in our early solar system, the sun condensed in its gas cloud (the remnant of some long ago super-nova). The heavier particles close to the new star were pulled in, imparting their energy into causing and then revving up the stellar rotation. As the gravity source began to rotate, it began to warp the fabric of space around it, pulling on the particles surrounding it and causing them to rotate. This rotation then in turn assured that most particles in the solar equitorial plane began to rotate in the same direction also ensuring that any further heavy particle bombardment of the young star would happen in the same direction of rotation. This might also serve to cause banding within the dust/debris disk there by causing ultimate planetary formation to occur.
This scenerio works weather on a planetary (Earth, Moon) level, Solar system level, or galactic level.
[/i]
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greatergood
- Ensign
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>all round bodies and most if not all other bodies rotate. I know of no rocks in space that do not have rotation
1) You're observing a universe that is 15 billion years old. Most galaxies currently in existence were well formed within the first billion years.
2) All the objects you refer to are infinitesimally small compared to galaxies and your spinning objects gained their rotational motion after matter has condensed into finite systems.
Even solar systems initally gained their rotational inertia most likely from shock waves from early supernovae that bent around large clumpy matter, imparting tangential forces to smaller clumps of matter.
That doesn't work so well for galaxies, because being composed of millions of stars, a supernova would have the net effect on a galaxy as a drop would have in a lake. And although that effect would have an extremely amplifying effect as the galaxy shrinks (due to the black hole in the center), I don't see how it could happen for all galaxies within the first 1 billion year period and suddenly stabilize such that those same galaxies look almost identical to all other galaxies we see from 14 billion years later (which is what they've found while comparing near field images to deep field images).
It just doesn't fit that it took only 1 billion years to form most of the universes galaxies with intricate and tightly spun arms, especially when nothing should have had spin immediately following the Big bang. What's more, the supernovae to generate spin-causing shock-waves should have been rare within those 1st billion years.
Regardless, I've done some more research on it, and the most popular theory is that galaxies spin as open systems due to tidal forces from the outside. Numerical methods seem to verify this too (see http://www.ifa.hawaii.edu/~barnes/ast626_97/tss.html). However what is causing these tidal forces is debated.
I'd also suggest this for more reading: http://xxx.lanl.gov/PS_cache/astro-ph/p ... 512013.pdf
1) You're observing a universe that is 15 billion years old. Most galaxies currently in existence were well formed within the first billion years.
2) All the objects you refer to are infinitesimally small compared to galaxies and your spinning objects gained their rotational motion after matter has condensed into finite systems.
Even solar systems initally gained their rotational inertia most likely from shock waves from early supernovae that bent around large clumpy matter, imparting tangential forces to smaller clumps of matter.
That doesn't work so well for galaxies, because being composed of millions of stars, a supernova would have the net effect on a galaxy as a drop would have in a lake. And although that effect would have an extremely amplifying effect as the galaxy shrinks (due to the black hole in the center), I don't see how it could happen for all galaxies within the first 1 billion year period and suddenly stabilize such that those same galaxies look almost identical to all other galaxies we see from 14 billion years later (which is what they've found while comparing near field images to deep field images).
It just doesn't fit that it took only 1 billion years to form most of the universes galaxies with intricate and tightly spun arms, especially when nothing should have had spin immediately following the Big bang. What's more, the supernovae to generate spin-causing shock-waves should have been rare within those 1st billion years.
Regardless, I've done some more research on it, and the most popular theory is that galaxies spin as open systems due to tidal forces from the outside. Numerical methods seem to verify this too (see http://www.ifa.hawaii.edu/~barnes/ast626_97/tss.html). However what is causing these tidal forces is debated.
I'd also suggest this for more reading: http://xxx.lanl.gov/PS_cache/astro-ph/p ... 512013.pdf
=================
PI-Rn't-Square. They're round.
PI-Rn't-Square. They're round.
Interesting that we tend to say that such a galaxy *is* "about 170,000 light-years across." In reality it *was* that size 25,000,000 years when the light we're looking at was generated. Who knows what it's like today.
So the "observable" part of the definition of size tells you how big a galaxy was, not is.
So the "observable" part of the definition of size tells you how big a galaxy was, not is.
Unfortunately there is no evidence that black holes spin and I doubt that they do. However, there is evidence that at the heart of every galaxy there exist a black hole. In fact it is thought that there is a relationship between the two. Meaning a galaxy cannot exist without one.
It doesn’t take deep thought to figure out that if you have a supply of matter and gas surrounding a black hole (for as far as the black hole's gravitational influence goes) the material will spin as a result of the hole's gravity force. Like water in a drain -the drain doesn’t have to spin to make the water spin.
It doesn’t take deep thought to figure out that if you have a supply of matter and gas surrounding a black hole (for as far as the black hole's gravitational influence goes) the material will spin as a result of the hole's gravity force. Like water in a drain -the drain doesn’t have to spin to make the water spin.
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greatergood
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- Joined: Sun Sep 04, 2005 3:35 am
It seems the story behind the science of galaxy rotation is quite interesting. (I've done a ton of research on this since my last post.)
The widely accepted theory today is called the "Tidal Torque Theory" or TTT, and was first proposed in 1949 by Hoyle. The idea is that after the big bang at time=0 there were irregular clumps of matter that pulled on each other via gravitational forces. An example case is where two oblong clumps of matter are oriented win a way where the closely oriented sections of the oblong clumps pulled more strongly on each other than the sections of the oblong clumps that were oriented further away from each other. Why? Because the strength of gravity is a function of distance. As a result, in this example most of the material would be torn away from the two clumps to combine into a chunk of dark matter - the remaining material was left to spin due to resulting shear forces within the clump of matter that wasn't torn away by gravitational forces, combined with the gravitational forces within the remaining clump to hold it together. This caused the initial spin - and formed the dark matter engine behind the formation of the galaxy.
Here's the interesting thing - up until recently (the last 10 years) there has been little to no evidence to prove TTT, but as stated by one physicist "One may even say that the wide acceptance of TTT is mainly due to the lack of any viable alternative theories rather than to clear predictions firmly corroborated by observation." - http://www.aip.de/groups/galaxies/poste ... metz04.pdf
I posted earlier that I had a hard time believing TTT was possible to account for spinning galaxies due to time constraints. In fact, I was right...without a "dark halo" it is not possible. In short, the resulting angular momentum from the above mentioned phenomena is on average: lambda=0.05; whereas the observed angular momentum for existing galaxies is: lambda=0.5. So, a rotational acceleration is necessary, and this acceleration is accomplished by an extreme shrinking of the whole galaxy as material condensed to form star systems - similar to how an iceskater spins faster when they bring their arms in. However, the radius would have to collapse by a factor of 100! That means that the all the milky way galaxy would have to come from matter as large as our whole galaxy cluster - making it intuitively impossible.
What's more, the time for this collapse to take place using current data is calculated to be 10^11 years - which is 7 times longer than the current age of the universe (1.5x10^10), let alone being within the first 100 Million years (10^8 ) which is the time frame that all evidence seems to suggest for this process.
So, to solve this connundrum, physicists theorized an initial formation of a "dark halo", a halo made of Dark Matter (DM), to have occured first at the moment of shear in order to accelerate the process. In fact, this "dark halo" mathematically works extremely well in creating a well formed galaxy in such a short amount of time, and is also very adept at balancing the galaxy into a stable structure immediately after formation - it's speed and size being controlled by the conservation of angular momentum. Further studies from an surprisingly good correlation between luminosity and rotational velocity has also indicated that the dark halo is the engine behind controlling the visible part of the galaxy that we are familiar with, forming the galaxy "from the inside-out: the disk scale-lengths with increasing mass as a function of time". - http://www.astro.rug.nl/~sctrager/teach ... diskev.pdf
Now I mentioned at the beginning of this post that until recently TTT was the prevailing theory simply due to the lack of other viable theories - there being little proof to support or reject it, but in the last 10 years that has changed. Due to numerical methods, N-bodies simulation have given the theory substantial credit. These simulations have resulted in a number of interesting discoveries, one being that over time galaxies should orient themselves perpendicularly to the galactic plane in which they exist.
As a matter of fact, it has been observed that all of our nearby galaxies are nearly perpendicular to the galactic plane in which we exist. According to one paper: "The detection of these and other non-trivial correlations between the spin and matter fields would serve to establish beyond doubt the validity of TTT as the origin of the angular momentum of spiral galaxies" - http://www.aip.de/groups/galaxies/poste ... metz04.pdf
In the last 5 years however there has evolved another model for galaxy formation involving the MOND (Modified Newtonian Dynamics) paradigm, which is radically different to the extent that it has quite the uphill battle in getting popular acceptance. It totally does away with Dark Matter. Proponents are confident that it does as good or better of a job explaining galactic formation as TTT does, but that's to be expected - right? Frankly I'd love to delve into it, but tonight my brain is full. If any other armchair astronomy buffs would like to research it and tell the rest of us what it means in plain english then that would be great.
More reading:
http://qso.lanl.gov/~laf/cosmopap/spin.ps
http://www.iap.fr/EnseignementStages/DE ... e/9_am.pdf
http://astro.ucsc.edu/~nng/webtalks/bullock.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0509/0509519.pdf
http://www.roe.ac.uk/~mlb/alignments/alignments.html
http://xxx.lanl.gov/PS_cache/astro-ph/p ... 512013.pdf
The widely accepted theory today is called the "Tidal Torque Theory" or TTT, and was first proposed in 1949 by Hoyle. The idea is that after the big bang at time=0 there were irregular clumps of matter that pulled on each other via gravitational forces. An example case is where two oblong clumps of matter are oriented win a way where the closely oriented sections of the oblong clumps pulled more strongly on each other than the sections of the oblong clumps that were oriented further away from each other. Why? Because the strength of gravity is a function of distance. As a result, in this example most of the material would be torn away from the two clumps to combine into a chunk of dark matter - the remaining material was left to spin due to resulting shear forces within the clump of matter that wasn't torn away by gravitational forces, combined with the gravitational forces within the remaining clump to hold it together. This caused the initial spin - and formed the dark matter engine behind the formation of the galaxy.
Here's the interesting thing - up until recently (the last 10 years) there has been little to no evidence to prove TTT, but as stated by one physicist "One may even say that the wide acceptance of TTT is mainly due to the lack of any viable alternative theories rather than to clear predictions firmly corroborated by observation." - http://www.aip.de/groups/galaxies/poste ... metz04.pdf
I posted earlier that I had a hard time believing TTT was possible to account for spinning galaxies due to time constraints. In fact, I was right...without a "dark halo" it is not possible. In short, the resulting angular momentum from the above mentioned phenomena is on average: lambda=0.05; whereas the observed angular momentum for existing galaxies is: lambda=0.5. So, a rotational acceleration is necessary, and this acceleration is accomplished by an extreme shrinking of the whole galaxy as material condensed to form star systems - similar to how an iceskater spins faster when they bring their arms in. However, the radius would have to collapse by a factor of 100! That means that the all the milky way galaxy would have to come from matter as large as our whole galaxy cluster - making it intuitively impossible.
What's more, the time for this collapse to take place using current data is calculated to be 10^11 years - which is 7 times longer than the current age of the universe (1.5x10^10), let alone being within the first 100 Million years (10^8 ) which is the time frame that all evidence seems to suggest for this process.
So, to solve this connundrum, physicists theorized an initial formation of a "dark halo", a halo made of Dark Matter (DM), to have occured first at the moment of shear in order to accelerate the process. In fact, this "dark halo" mathematically works extremely well in creating a well formed galaxy in such a short amount of time, and is also very adept at balancing the galaxy into a stable structure immediately after formation - it's speed and size being controlled by the conservation of angular momentum. Further studies from an surprisingly good correlation between luminosity and rotational velocity has also indicated that the dark halo is the engine behind controlling the visible part of the galaxy that we are familiar with, forming the galaxy "from the inside-out: the disk scale-lengths with increasing mass as a function of time". - http://www.astro.rug.nl/~sctrager/teach ... diskev.pdf
Now I mentioned at the beginning of this post that until recently TTT was the prevailing theory simply due to the lack of other viable theories - there being little proof to support or reject it, but in the last 10 years that has changed. Due to numerical methods, N-bodies simulation have given the theory substantial credit. These simulations have resulted in a number of interesting discoveries, one being that over time galaxies should orient themselves perpendicularly to the galactic plane in which they exist.
As a matter of fact, it has been observed that all of our nearby galaxies are nearly perpendicular to the galactic plane in which we exist. According to one paper: "The detection of these and other non-trivial correlations between the spin and matter fields would serve to establish beyond doubt the validity of TTT as the origin of the angular momentum of spiral galaxies" - http://www.aip.de/groups/galaxies/poste ... metz04.pdf
In the last 5 years however there has evolved another model for galaxy formation involving the MOND (Modified Newtonian Dynamics) paradigm, which is radically different to the extent that it has quite the uphill battle in getting popular acceptance. It totally does away with Dark Matter. Proponents are confident that it does as good or better of a job explaining galactic formation as TTT does, but that's to be expected - right? Frankly I'd love to delve into it, but tonight my brain is full. If any other armchair astronomy buffs would like to research it and tell the rest of us what it means in plain english then that would be great.
More reading:
http://qso.lanl.gov/~laf/cosmopap/spin.ps
http://www.iap.fr/EnseignementStages/DE ... e/9_am.pdf
http://astro.ucsc.edu/~nng/webtalks/bullock.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0509/0509519.pdf
http://www.roe.ac.uk/~mlb/alignments/alignments.html
http://xxx.lanl.gov/PS_cache/astro-ph/p ... 512013.pdf
Last edited by greatergood on Mon Mar 06, 2006 10:58 pm, edited 1 time in total.
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PI-Rn't-Square. They're round.
PI-Rn't-Square. They're round.
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greatergood
- Ensign
- Posts: 17
- Joined: Sun Sep 04, 2005 3:35 am
Water spins in a drain because of the rotation of the earth (it's a dot-product of the earth's rotation). On the other side of the equator it spins the other direction. At the poles and at the equator it doesn't spin at all going down the drain. This is true. Quite weird to see draining toilets not spin if you haven't seen it before.Martin wrote:Unfortunately there is no evidence that black holes spin and I doubt that they do. However, there is evidence that at the heart of every galaxy there exist a black hole. In fact it is thought that there is a relationship between the two. Meaning a galaxy cannot exist without one.
It doesn’t take deep thought to figure out that if you have a supply of matter and gas surrounding a black hole (for as far as the black hole's gravitational influence goes) the material will spin as a result of the hole's gravity force. Like water in a drain -the drain doesn’t have to spin to make the water spin.
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PI-Rn't-Square. They're round.
PI-Rn't-Square. They're round.
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harry
- G'day G'day G'day G'day
- Posts: 2881
- Joined: Fri Nov 18, 2005 8:04 am
- Location: Sydney Australia
The Galaxy spin
see links
http://imagine.gsfc.nasa.gov/docs/scien ... axies.html
http://imagine.gsfc.nasa.gov/docs/scien ... axies.html
Not all Black holes show a spin, that is because they have too much matter around them to show the spin or there has been a collision.
What we need to see is the start of a Black Hole. A neurton star or a possible quark star having a spin. These ultra dense matter, if they accumulate enough matter will turn into a huge mass that will stop light escaping and therfore give us the Black Hole as so to speak. Their spin is than hidden by outer collisions leaving dust clouds.
http://antwrp.gsfc.nasa.gov/apod/ap030601.html
http://antwrp.gsfc.nasa.gov/apod/ap031128.html
http://antwrp.gsfc.nasa.gov/apod/ap040908.html
http://antwrp.gsfc.nasa.gov/apod/ap970405.html
http://antwrp.gsfc.nasa.gov/apod/ap970121.html
http://antwrp.gsfc.nasa.gov/apod/ap960910.html
quark star
http://www.space.com/scienceastronomy/a ... 20410.html
Neutron stars
http://www.space.com/scienceastronomy/n ... 31203.html
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... tron+stars
Where does the galaxy gets its spin, one looks at the seed. The basic particals spin.
see links
http://imagine.gsfc.nasa.gov/docs/scien ... axies.html
http://imagine.gsfc.nasa.gov/docs/scien ... axies.html
Not all Black holes show a spin, that is because they have too much matter around them to show the spin or there has been a collision.
What we need to see is the start of a Black Hole. A neurton star or a possible quark star having a spin. These ultra dense matter, if they accumulate enough matter will turn into a huge mass that will stop light escaping and therfore give us the Black Hole as so to speak. Their spin is than hidden by outer collisions leaving dust clouds.
http://antwrp.gsfc.nasa.gov/apod/ap030601.html
http://antwrp.gsfc.nasa.gov/apod/ap031128.html
http://antwrp.gsfc.nasa.gov/apod/ap040908.html
http://antwrp.gsfc.nasa.gov/apod/ap970405.html
http://antwrp.gsfc.nasa.gov/apod/ap970121.html
http://antwrp.gsfc.nasa.gov/apod/ap960910.html
quark star
http://www.space.com/scienceastronomy/a ... 20410.html
Neutron stars
http://www.space.com/scienceastronomy/n ... 31203.html
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... tron+stars
Where does the galaxy gets its spin, one looks at the seed. The basic particals spin.
Harry : Smile and live another day.