How does our Galaxy maintain a fixed form?

[alpha2cen]

Our galaxy has maintained spiral style. But it is very large. How does it maintain a fixed shape?

We know gravity speed is same as light speed. And, our galaxy diameter is known as about 100 thousand ly.

[insane_alien]

simple, it doesn't maintain a fixed shape.

 

the reason it appears to is that it is so massive so changes(especially significant changes to its appearance) take millions and millions of years.

[granpa]

http://www.nicolascretton.ch/Astronomy/Galaxies/Disks/Disks.html

[alpha2cen]

simple, it doesn't maintain a fixed shape.

 

the reason it appears to is that it is so massive so changes(especially significant changes to its appearance) take millions and millions of years.

 

Then, why is our Galaxy thin plate form? Random form, it is too insufficient to explain the thin thickness. How does our stars in the Galaxy know their position well in the thin plate?

Edited February 1, 2011 by alpha2cen

[SMF]

The question hard to understand. I assume that gravity and rotation are main components of the orbiting disk like spiral shape, but I would like to know how the organization became flattened into a disk (like the solar system) rather than many different random orbits about the center. This appears to be a common motif. SM

[insane_alien]

Then, why is our Galaxy thin plate form? Random form, it is too insufficient to explain the thin thickness. How does our stars in the Galaxy know their position well in the thin plate?

 

false dichotomy. not fixed does not mean random.]

 

the stars do not maintain a fixed place in the galaxy, they orbit the center like the planets orbit the sun. even the apparent arms will fade and reappear over time. it's all moving but because the speed of light is so small comparatively it appears fixed.

[Sisyphus]

The galaxy's mass is mostly in a fairly flat disk shape for the same reason the orbits of all the planets of the solar system are close to being in the same plane. It's a spinning, gravitationally bound cluster of matter, and that is the plane of its total angular momentum. The spiral arms are not fixed structures, but waves of high density, like traffic jams on a highway.

[michel123456]

simple, it doesn't maintain a fixed shape.

 

the reason it appears to is that it is so massive so changes(especially significant changes to its appearance) take millions and millions of years.

 

If I am not mistaken, it is estimated that the Milky Way has made only 60 full rotations since the BB (and 59 since its birth). See Galactic year in wiki.

Edited February 1, 2011 by michel123456

[insane_alien]

exactly its huge. its enormously unfathomably huge.

 

and al lthat time stars have been exploding and being replaced, orbiting(those inside the suns orbit have orbited more and those outside have orbited less) the arms will have changed appearance considerably (they are really waves in the stars motion so they are under no obligation to move with the stars and can even move in a direction opposite to the rotation of the galaxy.)

 

you can see this behaviour crop up in even very basic simulations of a galaxy with only a few thousand 'stars' even if you start it off as a sphere or any old random shape. it can be done in less than 60 rotations too as most of the balancing tends to occur in the first 10-15 rotations and waves can form just as quick.

[davey2222]

The shape we see today of our galaxy is what it was 200,000 of years ago. But then again it might not be in that particular shape to begin with because light speed was not and is not instantaneous.

Edited February 10, 2011 by davey2222

[steevey]

Then, why is our Galaxy thin plate form? Random form, it is too insufficient to explain the thin thickness. How does our stars in the Galaxy know their position well in the thin plate?

 

There's gravity pulling from the center of the supermassive black hole which makes everything rotate at a pretty determined axis, but the galaxy isn't just a thin plate. The length may be like 200,000 light years across, but its not one star thick, its probably like at least 1000 light years thick, and thats just on the outer arms, and not in the galactic bulge.

[alpha2cen]

There's gravity pulling from the center of the supermassive black hole which makes everything rotate at a pretty determined axis, but the galaxy isn't just a thin plate. The length may be like 200,000 light years across, but its not one star thick, its probably like at least 1000 light years thick, and thats just on the outer arms, and not in the galactic bulge.

 

The ratio of thickness var diameter is about 1/100.

So we think that the Galaxy has thin thickness.

[steevey]

The ratio of thickness var diameter is about 1/100.

So we think that the Galaxy has thin thickness.

 

Well in that case, that's how matter formed around it and encircled around it in the black hole. There's an axis in which matter spun around and collected on, but matter could still be in other places besides that axis.