by Jyrki » Sun Apr 12, 2009 3:54 pm
To Case: Thanks for the remarks and for the data on the luminosity of these stars. Yes, for more accurate figures I should use a spherical region, *but* I should also use the densest 3D packing (that you get when you pile up identical size balls in hexagonally packed layers appropriately interlaced - imagine a pile of oranges or ball bearings if you like) as opposed to the cubical packing that I tried to use, when estimating the distance to the nearest neighbor. The changes would not likely be very dramatic given that the distance scales as the cubic root of the volume, so 190% density gives an expected distance of a factor less than cube root of 2 smaller. Significant, yes, but not for my purposes of trying to decide, whether the expected distance to the nearest neighbor would be 10 lys, 1 ly or 0.1 lys. Sorry about not making that clear right away.
To Chris: Thanks for the insight. Indeed, you correctly guessed what I was aiming at. I had been under the impression that we reside in a relatively sparsely populated region of the Milky Way, and was half expecting the difference to a cluster to be more significant in this respect. Of course, a relatively small change in the density will be enough to make a region of space stand out from its surroundings upon visual inspection.
To all:
Possibly an even bigger source of error in my calculation was the assumption of uniform distribution. Mutual gravity probably tends to make the center of the cluster denser than the perimeter. Anyway, before starting on anything more precise I would need to define exactly what I am aiming to compute. The average distance to the nearest neighbor from a *given* member star of the cluster (in which case I would take the average over all the stars belonging to a cluster), the average distance between two closest neighbors within a cluster (in which case I would take the average over several clusters of approximately the same type and size) et cetera. Undoubtedly such arithmetic has been done many times over,so let's not get into that here, and stick to the point of view of a star gazer moved onto a planet in orbit about a member star of an open cluster
On with the fantasy: would the dwellers of a compact cluster be more likely to work on interstellar travel? If the nearest neighbor is `only' a fraction of a light year away, it might not appear to be too formidable? Ok, given that at the moment a manned mission to Mars is about the limit of feasibility, we are still several orders of magnitude away from travelling even 0.1 light years
. Hmm, I'm forgetting something here. The presence of a nearby neighbor might spell trouble for the stability of any putative planetary system.
To Case: Thanks for the remarks and for the data on the luminosity of these stars. Yes, for more accurate figures I should use a spherical region, *but* I should also use the densest 3D packing (that you get when you pile up identical size balls in hexagonally packed layers appropriately interlaced - imagine a pile of oranges or ball bearings if you like) as opposed to the cubical packing that I tried to use, when estimating the distance to the nearest neighbor. The changes would not likely be very dramatic given that the distance scales as the cubic root of the volume, so 190% density gives an expected distance of a factor less than cube root of 2 smaller. Significant, yes, but not for my purposes of trying to decide, whether the expected distance to the nearest neighbor would be 10 lys, 1 ly or 0.1 lys. Sorry about not making that clear right away.
To Chris: Thanks for the insight. Indeed, you correctly guessed what I was aiming at. I had been under the impression that we reside in a relatively sparsely populated region of the Milky Way, and was half expecting the difference to a cluster to be more significant in this respect. Of course, a relatively small change in the density will be enough to make a region of space stand out from its surroundings upon visual inspection.
To all:
Possibly an even bigger source of error in my calculation was the assumption of uniform distribution. Mutual gravity probably tends to make the center of the cluster denser than the perimeter. Anyway, before starting on anything more precise I would need to define exactly what I am aiming to compute. The average distance to the nearest neighbor from a *given* member star of the cluster (in which case I would take the average over all the stars belonging to a cluster), the average distance between two closest neighbors within a cluster (in which case I would take the average over several clusters of approximately the same type and size) et cetera. Undoubtedly such arithmetic has been done many times over,so let's not get into that here, and stick to the point of view of a star gazer moved onto a planet in orbit about a member star of an open cluster :-)
On with the fantasy: would the dwellers of a compact cluster be more likely to work on interstellar travel? If the nearest neighbor is `only' a fraction of a light year away, it might not appear to be too formidable? Ok, given that at the moment a manned mission to Mars is about the limit of feasibility, we are still several orders of magnitude away from travelling even 0.1 light years :-). Hmm, I'm forgetting something here. The presence of a nearby neighbor might spell trouble for the stability of any putative planetary system.