[TML] average stellar intervals

[Timothy Little]

On Fri, Nov 16, 2007 at 09:26:54AM -0500, Garry Ward wrote:
> However, in the wonderful world of reality, is there an actual
> average distance between stars that has ever been calculated?

Based on RECONS data within 5 parsecs, the local density seems to
average 0.08 star systems per cubic parsec.  Data outside this range
is expected to be rather incomplete due to increasing numbers of red
dwarf stars undetectable by current means.


There is some ambiguity in defining "average distance between stars".

Firstly, binary systems and larger groups of gravitationally-bound
stars are quite common.  If you count the distances between the
individual stars in these systems, it will pull the average down quite
noticeably compared to looking at distances between systems.

One measure might be to average over all systems, the distance to the
nearest other system.  This works out to about 1.31 parsecs.  Again
this might be a low average in a sense, since jumping to nearest
neighbours will just get you to a dead-end pair.

Another plausible average might be the radius of sphere within which
there is an average of 1.0 other systems: 1.44 parsecs.  Though again,
this could be considered low depending upon how you want to use this
"average".

A different approach (closer to hex-map style) could be to divide the
universe into cells based on whichever system is closest, then average
the distances between systems in adjoining cells.  I.e. an average
distance to nearest systems in *every* direction, not just the single
nearest neighbour.  That works out to about 2.3 parsecs.

One other model is to work out the minimum jump distance that will
give you a 50:50 chance of being able to plot a path between any two
randomly picked stars, without any hop exceeding that distance.  The
threshold distance is 2.15 parsecs.

So you could pick any of these, or even devise more.


- Tim