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tommac
2011-Apr-13, 02:09 PM
if a galaxy's spin started to accelerate what would be the apparent change from the observations of say a star/planet on one of the outer arms?

I would assume that the galaxies in front and in back of the galaxy ( in the direction of the spin ) would get further away from it ...

Would ones that were further out from the center and further in from the center also get further away?

NEOWatcher
2011-Apr-13, 02:15 PM
Galaxies don't spin. The stars orbit.

Hornblower
2011-Apr-13, 02:20 PM
If we could magically accelerate all objects in the galaxy prograde in unison, they would fly apart from each other and from the center. If we increase their velocities enough, they could escape.

tommac
2011-Apr-13, 02:20 PM
Galaxies don't spin. The stars orbit.

OK ... but what if the stars orbited faster ?

NEOWatcher
2011-Apr-13, 03:09 PM
OK ... but what if the stars orbited faster ?
Hornblower said it well, things just get farther apart.
At least at first. If they don't reach escape velocity, they would go more elliptical. At apoapsis, they would start to head back to periapsis appearing to collapse, then it all starts again. (It's a basic concept of orbits)
The interaction of individual stars gets different because of local influences.

The bottom line is, you can't look at a galactic movement as a single object.

tommac
2011-Apr-13, 03:17 PM
Would the amount of mass in the galaxy or the spin of the SMBH in the center speed up the average orbital speed of the galaxy?

If we could magically accelerate all objects in the galaxy prograde in unison, they would fly apart from each other and from the center. If we increase their velocities enough, they could escape.

Strange
2011-Apr-13, 03:24 PM
Why would the mass in the galaxy cause it to speed up? That would imply that the orbits of stars in galaxies gradually get faster and faster; which I don't think they do (otherwise they would rip themselves apart).

The rotation of the black hole would have some local effects on accreting matter due to frame dragging but would be negligible elsewhere.

tommac
2011-Apr-13, 08:00 PM
How local is local?

Why would the mass in the galaxy cause it to speed up? That would imply that the orbits of stars in galaxies gradually get faster and faster; which I don't think they do (otherwise they would rip themselves apart).

The rotation of the black hole would have some local effects on accreting matter due to frame dragging but would be negligible elsewhere.

George
2011-Apr-13, 08:42 PM
Would the amount of mass in the galaxy or the spin of the SMBH in the center speed up the average orbital speed of the galaxy? If the mass of a galaxy suddenly increased for some odd reason -- two extragalactic SMBHs smashing into one another from opposite directions at the galactic c.g. -- then I assume the orbital velocities (galactic rotation) of the galaxy would increase during contraction.

loglo
2011-Apr-18, 06:40 AM
If the mass of a galaxy suddenly increased for some odd reason -- two extragalactic SMBHs smashing into one another from opposite directions at the galactic c.g. -- then I assume the orbital velocities (galactic rotation) of the galaxy would increase during contraction.

Remembering that galaxy kinematics are dominated by dark matter and not SMBH's, and discounting all that flinging of stellar matter all over the place, I doubt that doubling or tripling the SMBH mass would make a lot of difference in many galaxies.

George
2011-Apr-18, 03:36 PM
Remembering that galaxy kinematics are dominated by dark matter and not SMBH's, and discounting all that flinging of stellar matter all over the place, I doubt that doubling or tripling the SMBH mass would make a lot of difference in many galaxies. That's a good point considering the mass of the Dark Matter halo. There would be some local changes, but not on the whole without merging with another blob of dark matter, which I assume would require a galactic merger.

loglo
2011-Apr-19, 03:34 AM
That's a good point considering the mass of the Dark Matter halo. There would be some local changes, but not on the whole without merging with another blob of dark matter, which I assume would require a galactic merger.

Yeah, we seem to have swallowed a few dwarf galaxies without any large scale disruption so one with a bit of meat on its bones would be required.

WayneFrancis
2011-Apr-19, 03:45 AM
How local is local?
For a super massive black hole...much less then then the size of our solar system
like time dilation its effect drop off very quickly from the event horizon