# Re: SETI/ASTRO: MBrains/JBrains & Globular Clusters

From: hal@finney.org
Date: Tue Jul 17 2001 - 00:00:30 MDT

> > (a) Perhaps the objects are orbiting around the outside
> > of the cluster itself (maybe Spike would comment on
> > whether the velocity range 0.25 M_jupiter objects orbiting
> > around 10^5 - 10^6 M_sun objects is faster or slower than typical
> > planetary orbital velocities).

The formula is v^2 = GM/R. The question is then whether the radius
of the globular cluster is more or less than 10^5 - 10^6 the typical

Random google pages show globular cluster diameters at 100-200 ly.
Jupiter is 10 AU from the sun; Earth is 500 light seconds so Jup's orbital
radius is 5000 light seconds. 100 ly is 3 * 10^9 light seconds, so the
R ratio compared to Jupiter is aobut 10^5 - 10^6. This is the same
ballpark as the central mass ratio.

Based on this it does not appear that a planet orbiting a globular
cluster would have a velocity that is much different than typical
planetary velocities.

Hal

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