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 Post subject: dynamics of galaxies.
PostPosted: Sun Mar 06, 2011 3:01 pm 
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Hi everyone, sorry I’m late. I must apologize also for the abrupt way I left. The trouble is this forum is so addictive and I’m so long winded it was using all my spare time. Having said that I feel I must post this latest idea to see if it has any merit.
When it was proven that the outer parts of galaxies are travelling too fast for their orbits, it was decided there must be something stopping them from “flying apart” They called it Dark Matter and they have been trying to find it ever since.
Rather than spend years looking for something that may not exist why don’t cosmologist prove first that galaxies are in fact not flying apart.
I think they are indeed flying apart but not in the way scientist seem to think they should.
On several occasions I have seen scientist demonstrate this by flinging their arms out from their sides. I know this is a simple mistake, flinging one arm forwards and the other backwards would be nearer the truth, but when you are dealing with something as difficult to comprehend as a galaxy, you can’t afford to be slip shod.
If you tie a small weight to a length of cotton thread and swing it round above your head the centrifugal force acts in a straight line from the centre outwards. This is what holding your arms out from your side would demonstrate.
If the cotton was to break. Intuitively you would think the weight would fly outwards from the centre. It doesn’t.
When the cotton breaks, the centrifugal force disappears, instantly, so the weight carries on at the same speed but in a straight line at right angles to the direction of the centrifugal force.
It must be possible to detect the motion of a galaxy but to show how difficult it must be imagine a cart wheel that you know rotates once every two million years.
In the case of galaxies the cotton hasn’t broken it has become weaker, so the outer parts are not even moving away in a straight line but following a curved path but still travelling at their original speed.
This would be very difficult to detect, but other galaxies, in different “stages of their life” might give an indication that the spiral arms are slowly unwinding, or put another way, FLYING APPART.
All the best Maurice.


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PostPosted: Sun Mar 13, 2011 1:13 pm 
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Dear Maurice
I can only speak as an ordinary amateur astronomer, but I have observed and imaged a fair number of galaxies over my observing years.
Incidentally, I try to keep a fairly open mind about cosmological theories but I am not completely sold on "dark matter" or "dark energy" yet, but consider MOND (modified newtonian dynamics) another possibilty.
As I undertand things galaxies have existed over a considerable period of our universes generally accepted 13.7 billion years existence. However, as far as I know although there are many examples of galaxies merging or being distorted by mergers, there is no obvious observational evidence of any galaxies which have been left to their own devices falling appart when not affected by outside influences.
Best wishes from Cliff


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PostPosted: Sun Mar 13, 2011 9:32 pm 
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I think it is a bit more than "flying apart".

For example, if you look at the rotation curves of galaxies (speeds as you move out from the nucleus) then there has to be a lot of additional mass outside the visible part of the galaxy. And it is known as "dark Matter" because it is dark (in that we cannot see it).

My understanding anyway.

Ian
(waiting to to reprimanded ...)


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PostPosted: Mon Mar 14, 2011 10:42 pm 
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Hi Cliff, I thought things would get easier now I have a new lap top but they don’t. I have spent most of the week working out how to use the drawing tools. I finally managed some presentable diagrams which gave a good picture of what I’m on about but when I used the cut and paste the galaxies I had so carefully drawn literally did fly apart and ended up spread all over the clipboard.
Hi Ian, Perhaps it’s just as well I hit a snag because from what you are saying perhaps I have got the wrong end of the stick! Are you saying the outer parts of galaxies are travelling too fast and are flying apart because of Dark Matter?
As I understand it, any system of satellites, Suns moons or planets, in free fall round a gravitational centre, travel faster the nearer they are to that centre. Galaxies, like Saturn’s rings, have spokes or arms, which means things are reversed. The outer parts are travelling faster than the inner. This could mean that perhaps only the middle has the correct orbital speed. The inner would be too slow and would be falling to a lower orbit while the outer would be travelling too fast so would either, move to a higher orbit or even, reach escape velocity and leave the galaxy.
So what do you see as the problem with the motion of galaxies Ian and how does Dark Matter solveit?
All the best. Maurice.


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PostPosted: Tue Mar 15, 2011 9:49 am 
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As I understand things (but don't just take my word for anything), as you measure the speed of material (e.g. stars) rotating round, you do not find what you would expect. Ignoring the material close to the centre, as you move out you would expect the speed to decline (i.e. further out, slower speed) - as you said. However, this is found not to be the case (talking about Spiral Galaxies here). What is found is that as you move out so everything is travelling at around the same speed. Talking about distance per unit time speed here not angular speed. So why is material further out not travelling slower - and currently many think it can only be explained by dark matter throughout the galaxy and extending far out beyond the radiating regions. Of course there are other theories (e.g. MOND) and I cannot argue the merits of different explanations.

I just mentioned it in relation to the reasons for dark matter existing. The galactic rotation is interesting as it also throws light of the spiral arms. Because, with the speeds being moderately constant as one moves out from the centre, then why to the spiral arms not wind tighter and tighter (as material nearer the centre is taking a lot less time to go round than material further out) - but then one is into different discussions (off-topic).

I personally don't see dark matter is a massive issue (not a matter of "belief" :)). Maybe some think of it as just some kind of really exotic stuff that needs all sorts of weird complex physics to explain it. I just think of it as matter that does not radiate (or interact with radiation) - i.e. that we cannot directly see. But just because we cannot see it does not mean we cannot detect it indirectly (e.g. through its gravitational effects). Maybe it does involve all sorts of complex physics as well but I can see no problem with thinking there is matter around we cannot directly see but can detect. (Using the term "see" in the broadest sense in terms of detecting through radiation).

Just google "galactic rotation curves".

Ian
(Still not been reprimanded)


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PostPosted: Tue Mar 15, 2011 9:22 pm 
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dear Maurice
Regarding Saturn's so called spokes.
I tink the were first visually observed in the late 19th century but never seen very often. I know one chap who observed them in the early 1970s I think (I'll try to check that when I see him again) but from what I understand no coincidental visual observations were made by others and the chaps spoke sightings were not formally accepted. However, a fairly short time later spokes were imaged by a Saturn space probe and only then was the reality of Saturn's rings sometimes dislaying spokes accepted.
However, I gather it has now been established that the spokes in Saturn's rings are not like "solid" spokes in an ordinary wheel, Saturn's rings spokes are collections of dust
articles elevated above (or below!) the rings possible by some sort of electro-static force generated by the main rotating particles constituting the rngs.
Best wishes from Cliff


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PostPosted: Fri Mar 18, 2011 12:50 am 
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Hi Cliff. Thanks for the comments about Saturn’s spokes. The reason I mentioned them was to show the rings are rotating like a disc or a wheel, the inner parts with the same period as the outer. This indicates that the rings are not in normal gravitational free fall orbits. Incidentally, I believe the rings to be made up of electro statically charged particles and probably Saturn carries the same charge.
Because of the spokes or arms, I thought galaxies rotated in the same way, all parts with the same period, but thanks to Ian I now know different.
Hi Ian. I knew about the rotation curves but never bothered to check out the facts. I took it for granted they would prove galaxies are rotating like a wheel. The most obvious outcome of this would be that the outer parts would be travelling too fast. Now with the rotation curve data, this still seems to be the case, and what is often quoted, and erroneously demonstrated, is that they should be flying apart.
This is what I latched on to, and of course I have my own, very nuts and bolts theory, of how it came about. A corner stone of my argument is the fact that things “fly off” at a tangent, not straight out from the centre, so consequently are much harder to detect.
The fact that scientist say “SHOULD, fly off” implies that they don’t, and as I believe this would be harder to detect than looking at rotation curves, raises the question, do they know for definite that they are not in fact “flying off”. If it is not known for sure, why invoke Dark Matter. This would be like saying “we don’t know if the galaxies are flying apart or not, so we will look for Dark Matter to prove they are not”!
This would have been much quicker had I been able to transfer my diagrams from notebook to the forum, I’ve been trying all week; It would be quicker to send in the back of the envelope!
Thanks for the input Ian. More on the nuts and bolts later. All the best Mauice.


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PostPosted: Fri Mar 18, 2011 9:48 am 
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maurice wrote:
Hi Ian. I knew about the rotation curves but never bothered to check out the facts. I took it for granted they would prove galaxies are rotating like a wheel. The most obvious outcome of this would be that the outer parts would be travelling too fast. Now with the rotation curve data, this still seems to be the case, ...


Look again at the rotation curves because they are NOT rotating like a wheel !! And that is a very very important fact.

I am very confused as to where you get the "should be flying-off" from because there is gravity and how much force that "provides" depends on the masses and distances.

I have never come across this "flying apart" idea - could you provide some links maybe ?

Ian


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PostPosted: Fri Mar 18, 2011 11:30 am 
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You could google on "Vera Rubin" who did the pioneering work.


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PostPosted: Fri Mar 18, 2011 2:37 pm 
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stella wrote:
You could google on "Vera Rubin" who did the pioneering work.


Had a search on her name and all I could find were the details on galaxy rotation curves and nothing about galaxies flying apart.

Ian


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PostPosted: Fri Mar 18, 2011 8:56 pm 
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Hi Ian, There are many references to the “Fact” that stars are not flying off when they should be. When I google’d, Vera Rubin, one site that came up was, vera rubin biography from answeres .com.
Scroll all the way down to “Discovered Dark Matter. Read through it and you will see. What was keeping them from spinning away? And. Andromeda was moving at a fast rate but stars were not spiralling away from it. And. Some kind of matter to keep them from ...out of the Galaxy.

I have read a lot of these accounts of Vera Rubin on google and they all say the same thing. The stars are all moving at the same speed as you move away from the centre. Why does no one ask the question you asked, “If they are all travelling at the same speed and the outer have the longer journey, why are the arms not winding themselves into tighter spirals?”

There are a number of animations etc that showed galaxies spinning as a wheel spins! This doesn’t tie in with the rotation curve data. Very confusing.

The comment I made about the rotation curve data, meant that even though this proved the galaxy didn’t spin like a wheel, it still showed the outer parts are travelling too fast so should be moving to wider orbits.
All the best. Maurice.


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PostPosted: Fri Mar 18, 2011 10:02 pm 
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maurice wrote:
Why does no one ask the question you asked, “If they are all travelling at the same speed and the outer have the longer journey, why are the arms not winding themselves into tighter spirals?”


They do ask the question - whole section of my studies on galaxies about the "Spiral Winding Problem". And theories/answers were in the nature of the spiral arms. As the spiral arms rotate so stars and material moves into and out of the arms (i.e. they act a bit like waves in the ocean or pressure waves). Thus the spiral arms need not rotate at the same speed at the matter.

Regarding the "flying apart" question I guess it depends on the way you look at it. I take the question as why is the matter moving at the same speed (i.e. what is driving it to travel at such a speed) rather than given the observed speeds, why is it not flying apart.

Ian


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PostPosted: Sun Mar 20, 2011 12:03 am 
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Hi Ian. Do you have an explanation for the speed being the same?
All the best maurice.


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PostPosted: Sun Mar 20, 2011 9:31 am 
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maurice wrote:
Hi Ian. Do you have an explanation for the speed being the same?
All the best maurice.


I have no explanation myself - I only consider the explanations of others and form my own opinion on those. Thus I can offer nothing additional to those other theories other than an uninformed vote based in partial understanding (remembering that the various theories have been proposed by others with far more knowledge, experience data, etc. that myself).

Personally I favour the Dark Matter explanation. Part of my preference might be a lack of understanding of things like MOND and part because I don't see dark matter as anything weird and exotic. Just because it does not emit or interact with radiation just means we detect it in other ways. There are lots of things we infer the existence of indirectly (e.g. cannot see) and then study. And being based on theories, so it is likely that our understanding will develop and change with time, new data and discoveries in other areas of research.

Ian


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PostPosted: Sun Mar 20, 2011 4:30 pm 
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Hi Ian. I realised you favour the dark matter idea. What I am asking is how does it work. Is it just like ordinary matter except not visible? If so, how does it cause the galaxies to break the Newtonion and Keplarian rules of orbital dynamics?
All the best Maurice.


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