Dark Matter sheds some light

The non amateur stuff. Hawking, black holes, that sort of thing

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joe
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Dark Matter sheds some light

Post by joe »

It turns out that we are bigger than M31 after all. Some NEW INFORMATION about not so cold dark matter has got cosmologists all excited and has allowed them to work out its speed, temperature and how much it weighs.
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Vega
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Post by Vega »

Great stuff,

This should mean the geniouses out there that are astro-physiscists will be carrying out new experients in new ways. Who knows what new discoveries will be made.

Kinda nice to know we live in a BIG ASS galaxy. Us humans needed to hear that if you look back through history we've had some real "kick in the teeth" discoveries...

1. Earth actually isn't at the centre of the universe :(

2. The Earth goes round the Sun not the other way round :?

3. Earth is not in a special position at all in the solar system (apart from being in the right place to harbour life as we know it). :(

4. Our sun is quite average compared to others (oh and will engulf our planet in a few billions years!) :roll:

5. There are literally billlions of stars just in our own galaxy :?

6. Our solar system is in no way a 'special' position in our galaxy :?

7. Our galaxy is one of billions of others :x

8. Our galaxy is one of the largest in it's vacinity :D

One other nice fact is that we have found no other planet that resembles anything like our own yet, which I feel is still very special. If there is alien life out there searching for planets as we are, imagine what they would think if they came accross ours in their sights ??
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Cliff
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Post by Cliff »

Dear Joe
Thanks for the "dark matter" story information.
I only managed a quick read as yet, so I may have missed some important points. However, at first glance the story seems a bit vague, perhaps its brevity means vagueness is inevitable.
I already read elswhere some time back that the Milky Way had been assessed to be much bigger than previously thought!
However, if I read correctly "dark matter" has temperature, although i do not think the article says how high "dark matters" high temperature is.
Whatever, what effect, if any, does dark matters temperature have with respect to the currently assessed CMB value.
I am also inclined to suggest that since if i read correctly dark matter exists in sort of clumps (not less than 1000 light years across, is it possible to be just another way of interpretting the "old" MOND theory idea.
Best wishes from Cliff
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Post by Phil Rice »

Wow.

Proof that us Brits are at the leading edge of research.

Absolutely brilliant!

Phil :lol: :lol:
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Post by stella »

"Proof that us Brits are at the leading edge of research."

Only problem is that Prof. Gerry Gilmore is a Kiwi from
Christchurch, N.Z.
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Post by davep »

That's how national pride works though isn't it? If some of the work was done in an institution in our country then we can be proud -- no matter if the work was done by someone from elsewhere. On the other hand, if the work was done in an institution in another country, but by someone born here, we can also be proud.

It's a bit like the BBC running that British design classics poll thing at the moment. In there you've got the Mini and the World Wide Web. Sir Alec was born in Turkey, but he lived in the UK when he designed the Mini -- so that's okay. The HTTP protocol and HTML were designed by Sir Tim while working at CERN -- but that's okay 'cos he was born in the UK.
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Post by Phil Rice »

Dear Stella,

Get a grip. Stop being so pedantic. I'm leaving.

:cry:
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Post by joe »

Cliff wrote:I already read elswhere some time back that the Milky Way had been assessed to be much bigger than previously thought!
Yes this is true, but I believe this is the first time that there has been enough evidence to say that the Milky Way is actually bigger than the Andromeda Galaxy.
if I read correctly "dark matter" has temperature, although i do not think the article says how high "dark matters" high temperature is.
10,000 degrees. (But you may have already re-read the article)
I am also inclined to suggest that since if i read correctly dark matter exists in sort of clumps (not less than 1000 light years across, is it possible to be just another way of interpretting the "old" MOND theory idea.
In what way? They are saying it's because the particles are moving too quickly to be "pushed" together further. MOND, if true, has an effect when the gravitational force between bodies is very small, is that right? Does not MOND theory try to explain the rotation curves of galaxies without the need for Dark Matter. If these researchers have discovered the temperature, size and speed of matter that can't be seen, doesn't it then negate the need for a theory that says it (DM) doesn't exist?
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Post by Cliff »

Dear Joe
Thanks for responding.
No, I have not got round to re-reading the BBC article yet. So your further comments are very helpful.
I was talking off the top of my head so what I said might be rubbish - and at least on this particular topic might continue to be so.
Like you say I do not know quite if\how Mond theory explains the galaxy rotation problem. However, I am not sure exactly how dark matter or dark energy does either (unless someone knows dark matter\energy's distribution.
By the way, I think there is a BBC horizon about dark matter this coming thursday night - so perhaps all will be revealed.
Dare I say it, but it had peviously occurred to me that perhaps cosmolgists had previously been unable to explain the galaxy rotation problem possibly because there being so much ordinary matter in all sorts of little bits ie relative to the size of a galaxy,eg stars, gas, dust and other odd-ments in various forms, that we (astrophysicists cannot satisfactorily analyse the rotation of galaxies problem.
I am possibly being a bit naive in saying that, but as far as I know even the three body gravitation problem is still something of a headache. using sophisticated programmes it seems possible to assess the positions of our solar system planets for umpteen thousand years, but beyond that current prdictions fall down (I THINK!?).
If that is the case then it occurred to me just possible that there are so many "bodies" and other "rubbish" rotating around the galaxy that irespective of the accruacy of cellestial dynamic theory, we still may not have enough computer power to handle the problem - or may be the problem is unhandleable?
With regards the temperature of dark matter, which I think you mentioned the BBC article suggests is 10,000 degrees K-ish. I must confess to having dificulty getting my head around this as well. However, it has occured to me that the apparent high temperature of dark matter might be a peculiar thing a bit analagous to the originally unexpected high temperature of the outer atmosphere of our Sun, which at least is semi-explained by saying something like the Sun's outer atmosphere is very tenuous, so even though its temperature is very high the actual total energy is quite low, and magnetic fields may be also a factor. Please excuse that rather simplified discussion.
Whatever, I'll try to read the BBC article properly before I spout anything else about this issue I nearly said matter (not issue) but I thought better of it !
Best of luck from Cliff
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Post by Cliff »

Dear Joe
Perhaps I should keep my trap shut, but I just had another, qick read through the BBC article. Arguably I am still as confused as ever, but I thought I would cause more mayhem.
From what I gather the Dark Matter 10,000 degree temperature value has been assessed from the minimum clumps (or whatever) being 1,000 light years across and an somehow determined speed for the "particles".
Now I can accept that, I think, but cannot help wondering how accurately the values are known\assessed. Whatever, the related particles are, and I think the article suggests wimps as candidates, then presumably\possibly if they dark matter can only exist in big clumps (1,000 light years across-ish) then if they can be created in any sort of "ordinary" particle accelerator, then at best the created particles could only be very short lived? I suppose that is quite possible because there are a variety of particles created from time to time that don't live long.
Well, I must say i await developments on this dark matter topic with interest, even if without much understanding on my part.
Best wishes again from Cliff
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Post by joe »

Cliff wrote:Dear Joe
Perhaps I should keep my trap shut
No, I don't think you should, Cliff. It always helps to have different perspectives on these very complicated subjects. I only know a little about MOND and had to refresh my memory when you mentioned it which led to a little more information on the subject of dark matter.....so, all comments welcome as far as I'm concerned. I am as confused as the next person, but it's a nice feeling knowing that the "answer" is "out there". :roll:
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In the dark..

Post by brian livesey »

There's a dark matter HORIZON programme tomorrow evening on BBC 2. :wink:
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Re: In the dark..

Post by joe »

brian livesey wrote:There's a dark matter HORIZON programme tomorrow evening on BBC 2. :wink:
I've already seen it. There will be many talking heads (physicists and astronomers - mainly american, with an Italian - adds scientific authority) standing either inside an observatory or outside or an untidy office, with repeating wizz-bang computer graphics of rotating galaxies and the early universe and no real conclusion at the end.
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Post by KendalAstronomer »

unless someone knows dark matter\energy's distribution
From what I think I've heard, DM is supposedly in a 'halo' (at least a large sphere of falling off density) around the galaxy. There is a matter halo, with various clumps and clusters dotted around, but they rotate with the disk. The disk rotates closer to a solid object than a disk of matter with a falling off mass distribution. This means either there is an increase in density towards the edge of the galaxy, or the matter is suspended in a halo of matter that falls off in density less quickly than ordinary matter, which hasn't been observed and which exists in a more even distribution through the halo than matter does, lying in a disk.

Computation isn't the only way to calculate the effect of baryonic (ordinary matter) dark matter - such as brown dwarves, dust, dimmer stars etc - and three body mechanics isn't required when considering the overal field of influence on interstellar scales. The mechanics of galaxies have been calculated many times using many assumptions, including build ups of baryonic dark matter, but each one runs into problems. The baryonic matter would drift into the disk far too early to maintain solid body rotation being the major problem. Something is required that drifts slower, produces gravitational fields and interacts less with baryons, so it won't be pulled into the disk when baryons make their way. Weakly Interacting Massive Particles.

That's how I think of it, at least. Sure there are counter arguments, but difficult to get high resolution images from other galaxies, difficult to calculate, difficult to simulate and with our own galaxy, there's always the can't see the wood for the trees problem... Need to get round one of those problems to nail any particular theory.

Star formation theories also explain why cosmologists don't use alot of baryonic dark matter - it locks itself up when it clumps enough to create a strong gravitational field over the billions of years it has been around.
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Post by Cliff »

Dear Kendalastronomer
Thanks for the comments.
I am pleased that you mention (or think you do) that cosmologists use various ways of assesseing the galaxy rotation problem (without needing to worry about the three body problem). If I got your meaning correct it seems that cosmologists are still struggling quite a bit. and that cosmologists are still a long way from agreeing about these things. However, I can understand why someone like me could have difficulty with the the three body problem. However, I cannot really get my head round understanding how the complexities of galaxy rotation can be satisfactorily answered, if the three body problem is still a problem.
There is an interesting article in this weeks New Scientist about black holes and the possibility of the odd extra dimension, or two.
Best wishes from Cliff
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