Formation of galaxies..?

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

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RL Astro
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Joined: Tue Jan 24, 2006 6:09 pm
Location: Plymouth

Formation of galaxies..?

Post by RL Astro »

Dear all. Thanks for wasting time to read my rants and could I ask you to try not to fall asleep halfway through :lol:
Has anyone got any ideas how millions and millions and millions of stars come together (galaxy) and leave none just floating about on their own (stars not in a galaxy)? I heard a theory on TV the other day (I was watching Horizon) that seemed to have a fairly logical answer. Big Bang...went bang, and loads of things were ejected. So loads of "balls" of hydrogen gas were floating about. I think most theories agree up to this point, but then they go off in 2 ways:
1) Stars were formed as loads of gases came together and formed nebulae, and they were kept together as galaxies because they were all pulling on each other with gravity. The black holes in the centre are just there because the galaxies oldest star exploded and formed it.
2) The "balls" of gas collapsed and exploded, creating a black hole and blasting off loads of matter and gas that formed nebulae and stars, and were always rotating round the black hole. In this case the black hole was there before the galaxy, and it would even suggest that black holes existed even before stars. Astronomers call these "supermasive black holes", presumably cause they're not formed by a supernova but other means, and they're big.

Personally I believe the second one. Can anyone clarify these theories or tell me any others? Just curious. Space is, after all, a very curious place.
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Post by GordonCopestake »

As far as my understanding goes, when the universe was formed hydrogen gas was relatively evenly distributed throughout the universe with just slight areas of higher density.

As these small areas of higher density had a higher mass their gravity pulled other bits of gas towards them to form small clumps. This is a run away phenomenon and happens over millions of years.

The gas clouds become huge, millions of light years across. The super massive black holes you describe form when the centre of the gas cloud collapses under it's own mass and forms a singularity. The shockwaves from this violent event cause the remaining gas in the cloud to coalesce into stars (maybe).

The reason the galaxies have "clear space" between them is because the gas from these areas has been swept clear into the surrounding galaxies.

As for your other question about stars forming outside of galaxies, as far as im aware, stars do not form outside of there parent galaxies, however they can leave these galaxies once formed. Perhaps after an event like two galaxies colliding, or some other event that "gravity assists" the star out of the galaxy. Maybe a blackhole passing close or some other massive body.

I believe there is some structure to the layout of the galaxies too, and after some quick googling i came across this.

An image from the above link showing supercluster structure

I doubt i have it all correct in my mind, but i hope this helps.
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Post by austin »

I believe there is some structure to the layout of the galaxies too

I am pretty sure that actually it is the supercluster (of galaxies), rather than individual galaxies that are deemed to be the smallest workable 'unit' as it were, of the universe. So indeed, there is a uniformity of the supercluster as Gordon rightly points out.

120mm skywatcher refractor f8.3, 10x50 bins
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