Expert: Jayendra Upadhye - 2/3/2006

Question
Hello.

I read about how our sun moves round with the galaxy at 1 million km an hr and it takes 250 million years to complete a cycle.

However, is the above refering to the galaxy spinning round itself or the galaxy orbiting something else?

If it refers to the galaxy spinning round itself, do galaxies also orbit other things?

Do galaxy clusters spin round themselves and orbit other things too? What about superclusters? Someone told me that superclusters revolve round a central point. Is that a supercluster?

I'm sort of trying to get a general idea of what's revolving around what. is all this revovling caused by gravity and inertia?

Thanks. Steve.

Answer
Hi,
Good question steve,
I must point out though that "Inertia" has nothing to do with all this!

Inertia is just plain old "resistance to motion"! period.

Yes gravity is the root cause of all this tumbling around we see, and the fact that the universe is truly HUGE!

Lwt me set things in perspective so you will understand on your own.
1 - Nothing in this universe is exempt from gravity.
2 - Glaxies too are susceptible to this, and so routinely form groups, clusters and super clusters (virgo cluster and coma cluster and abel cluster)
3 - Clustered galaxies do orbit around the ever shifting center of gravity of the cluster. And even collide with (pass thru) each other. Elliptical galaxies are remnants of such clashes.
4 - close to home, the large and small magellanic clouds orbit the milky way. So do the twin satellites of the M31 Andromeda Galaxy, orbit that galaxy. Together they all form the local group of galaxies, and are speeding towards the virgo cluster at about 300 km / sec (i may be wrong there, check it out on the web).
5 - Lastly ALL galaxies turn about their center of gravity.

So!
Hope that suffcies.
Jayen