Question about the spiral shape of galaxies

[Richardisgreat]

Iv been wondering for a while why some galaxies have the familiar spiral shape we often see. Is it the effect of dark matter and gravity squashing them into a thin disk shape? Is it the super massive black holes that are found in the center of some galaxies sucking everything in like water going down a plug hole and formimg spirals as they fall in?

Also i have noticed that if you wind the clock back and unravel the galaxies and count how many turns the center of some galaxies must have made to form the spirals we see then it seems to be aound 2 complete turns, i was wondering if that is because everything is really slowly falling into the center and in the past 13.8 billion years thats how far it has progressed?

As always i appologise for asking questions that might be common knowledge to some people, its only my 6 year old daughter has been asking questions about galaxies that i dont know the answers to and of coure i want to tell the truth as much as possible I guess we want to know why spiral galaxies take on the common shape the do.

Thanks in advance guys and gals

Richard and Holly

[nephilim]

I believe its the black holes at the galaxies core.....I may of course be completely wrong

Steve

[Knight of Clear Skies]

It's a very good question, and from what I've read I don't believe it's not fully understood. It's fairly straightforward to understand why a galaxy forms a disc: the answers in this thread concerning Saturn's rings should help you. The wiki article is a good starting place for understanding how the spiral arms may form, but it's the kind of thing that requires supercomputer simulation to model properly.

One point to consider: individual stars move in and out of the arms as they orbit the galactic centre. The arms are regions of average higher star density; they arms don't keep their structure as the galaxy rotates. If you were to look at look at Andromeda in x million years, it would appear somewhat different rather than a simple rotation of its current appearance.

(Incidentally, there are very, very few stupid questions in science.)

[Daddystu]

From what i've read i've always thought that galaxies begin their lives as spirals, then over time either 'lose their arms' becoming barred spirals > ellipticals. Spirals may also merge to become elliptical due either to the collision or possibly different/opposite spin rates.

Its certainly an interesting question you pose. The following graphic kind of helps explain what i mean;

http://www.google.co.uk/imgres?imgurl=http://universe-review.ca/I05-14-galaxyevolution2.jpg&imgrefurl=http://universe-review.ca/F05-galaxy.htm&h=500&w=731&sz=101&tbnid=00AKa3IdlHQ-QM:&tbnh=90&tbnw=132&prev=/search%3Fq%3Dgalactic%2Bevolution%26tbm%3Disch%26tbo%3Du&zoom=1&q=galactic+evolution&usg=__bTsRWD7l3JsQJ12lKVaUVgK8IZY=&docid=uARlEBGFKVTkxM&sa=X&ei=pZtNUcu0HYXXPMnvgeAF&ved=0CFYQ9QEwBw&dur=157

[Monty]

Until we know more about dark matter and energy I'm a little sceptical about the google reference.

[Richardisgreat]

Thank you for all your feedback guys, it was actually a question posed by my 6 year old daughter, she is a bright spark, She has a surprising amount of understanding with regaurd to star fomation and solar system formation. The really big question she keeps asking is what caused the big bang I havent introduced her to the concept of a multiverse yet lol. At her school at the moment they are teaching that god made eveything the stars, the planets and life on earth etc. However i think she knows better but has to keep quiet She is desperate to look through my scope however its usually too cloudy or past her bedtime when i get the chance to get it out. We have agreed that in the school holidays she can stay up later and clouds permitting she can have a look. I just know there will be lots of ooos and arrrs and wooows

Thanks again guys

[Daddystu]

Until we know more about dark matter and energy I'm a little sceptical about the google reference.

I agree on the galactic formation part. I was more pointing towards the spiral to elliptical evolution steps.

[Richardisgreat]

Would i be right in thinking that when some large stars die and form blackholes, they then attract and consume other nearby black holes until a supermassive black hole is formed. When this happens they slowly (or quickly depending on which way you look at it) eat up everything around it thus becoming the centre of a spiraling feeding frenzy - Galaxy ? then from the gravity of the galaxy other nearby galaxies are attracted causing galactic collisions and supermassive blackholes merging etc etc. Until our local group will all eventually come together? however space keeps expanding but all the matter is swallowed up, so we will be left with a big empty universe with one central blackhole with nothing left to consume?

This kind of explains the big bang theory happening everywhere at once if we say that empty space was already there but there was no time as there was no matter, so how can we have space with no matter, hmm my brain is hurting now and its lunch time

Im sure im presuming far too much, maybe i should go to church

Anyone got any good theories on life the universe and everything?

[Richardisgreat]

and please dont say 42

[Daddystu]

Would i be right in thinking that when some large stars die and form blackholes, they then attract and consume other nearby black holes until a supermassive black hole is formed. When this happens they slowly (or quickly depending on which way you look at it) eat up everything around it thus becoming the centre of a spiraling feeding frenzy - Galaxy ? then from the gravity of the galaxy other nearby galaxies are attracted causing galactic collisions and supermassive blackholes merging etc etc. Until our local group will all eventually come together? however space keeps expanding but all the matter is swallowed up, so we will be left with a big empty universe with one central blackhole with nothing left to consume?

This kind of explains the big bang theory happening everywhere at once if we say that empty space was already there but there was no time as there was no matter, so how can we have space with no matter, hmm my brain is hurting now and its lunch time

Im sure im presuming far too much, maybe i should go to church

Anyone got any good theories on life the universe and everything?

I'm no cosmologist but I think if there remained only one supermassive black hole then all the matter in the universe at present would be contained within its point singularity. However, I think Hawking demonstrated that black holes themselves can radiate energy over time and eventually dissipate. So presumably we'd be left with a soup of low energy subatomic particles floating around uncombined at absolute zero?

[Richardisgreat]

I wonder if all those subatomic particles would come together under there own gravity? Yeah its a mind boggler for sure. It sounds a bit like the big bang, big crunch theory. If at absolute zero a new big bang happens after all didnt prof brian cox say that energy cannot be used up but only changed? So all the energy in the universe is concentated at the same point and the big bang occurs in a space that exits without time, and time and all the matter is reborn?

By Jove i think we have sust it