NGC300

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

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Cliff
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NGC300

Post by Cliff »

Dear al
According to articles I have read apparently recent observations with (I think the Gemini scopes in Chile) suggest that NGC300 is much lareger than previously thought. There seem to be possible implications that the Milky Way might also be significantly bigger than currently thought. Presumably if the above things prove to be true (or at least possibly true!) they could have some implications related to the mass of at least some galaxies and things like "dark energy" and "dark matter".
Best wishes from the Grumpy Old codger Cliff
KendalAstronomer
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Post by KendalAstronomer »

I think this depends on what the observations actually say. Are they saying that the galaxy is larger or more massive? Is the visible region of the galaxy 'larger' than previously thought or the halo? Also, the increase in mass would have to be incredible to have any impact on the overwhelming mass of the universe thought to be locked in Dark Matter and Dark Energy. Previous estimates of galactic and universal mass have come from galaxy dynamics and how different massive objects interact via gravity both internally and externally. If you have a large spiral galaxy, for example, with no way to explain why the arms haven't flown off or developed more differential rotation along their length, then these questions remain no matter how estimates of the galaxy's mass or size change. With so much of the Dark Matter and Dark Energy theory centred around relative measurements of mass etc, changes in the absolute measurements haven't always the impact that they would have in some other theories.

Admittedly, for all that I know, the world's cosmological community could be waving a white flag and writing a paper of surrender to be presented to Gemini at this very moment...
Cliff
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Post by Cliff »

Dear Kendalastronomer
I am afraid that the articles I have read were both very limited in scope (i do not meam that in the telescope sense of course). If I read things correctly the articles only referred to observations of just one galaxy (ie NGC300). So I was quite surprised it seemed to be being extrapolated as much as the articles seemed to say. However, I think the suggestion was that stars extended much further out than had previously been thought, and I think it suggested in the haloe as well. Presumably that could also make the galaxy much more massive than previously thought. I got the impression as well that the implications might be that our Milky Way could be as much as 200,000 light years across. However, it occurred to me that the article might be really just using the Milky as an example of what it would be like if the if the observations had related to it - so that bit may be a bit ambiguous.
I am personally am interested in galaxy dynamics (not particularly because I understand them or could ever hope to contribute to the subject but because from what I gather the dynamics are very complicated and unlikely to be solved buy ordinary mathematics. From what I read I am not even sure that current computer technology is actually up to properly sorting these issues out.
Of course unlike "simple" solar systems, whereby the central star tends to be pretty massive relative to the orbitting planets, galaxies are very different, by all accounts even the likely black holes in the middle of galaxies are relatively puny compared with the overall mass of the stars orbitting around the galaxy. From what I gather at least some cosmologists take the view that the spiral nature of galaxies is not caused by the actual stars which just keep orbitting in much the same way, but by the gas and dust which is more affected by gravity waves and such like. As far as I know though one problem is that although gravity waves probably fit with theory no one as actually "observed" them yet.
Whatever, the articles seemed to be suggesting that many more observations of NGC300 and other galaxies are needed to confirm the Gemini observations and also check out many more galaxies.
Incidentally a talk I attended by a cosmologist mentioned that there could be as many stars between galaxy spiral arms as in the arms themselves. However, the stars in the arms are very bright, many being relatively young stars born out of the dust in the spiral arms. The stars between the spiral arms being much fainter.
Best wishes from the Grumpy Old Codger Cliff
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Post by joe »

Cliff wrote:From what I gather at least some cosmologists take the view that the spiral nature of galaxies is not caused by the actual stars which just keep orbitting in much the same way, but by the gas and dust which is more affected by gravity waves and such like. As far as I know though one problem is that although gravity waves probably fit with theory no one as actually "observed" them yet.
Would that be density waves Cliff? Density waves are waves that travel around the galaxy more slowly than the stars and when stars and dust meet these waves they are forced to slow down rather like cars that meet a traffic jam, they slow down then move off, a bit like a concertina effect. While the dust is caught in this density wave it is compacted a bit more and the formation of stars is accelerated.

You rightly say that gravity waves have not yet been detected but I'm not sure they would have any measurable effect on ordinary matter in the disc of a galaxy.
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
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