Re: Nearby stars-why do they start at 4LY?

"John C. Polasek" <jpolasek@xxxxxxxxxx> wrote in message news:5b9784dng0s0hkgu94con8409ur7kiatqg@xxxxxxxxxx
Wiki et al show tables of the first 20 or 50 starsnearest the earth.
The distances for the first few are
.. .. .. 4.3 6.0 7.7 8.4 8.6 9.4 10.4 LY
1.7 1.7 .7 .2 1.2 1 the differences
Why are there no stars from 0 to 4.3 LY? From the difference list
there should be at least 2 closer than 4.3.
These are probably the few that can be measured using the parallactic
effect. It just doesn't seem likely that such a void exists.
John Polasek

If you actually do the arithmetic on star density in our Galaxy, 4 LY is just about the diameter of a sphere containing one solar mass. So there is no mystery about why the nearest star is 4.3 LY away.

Very roughly:

galaxy disk diameter 100,000 LY
disk thickness 1,000 LY

Disk volume pi R^2 x T = 3.14 (50,000)^2 x 1000 ~ 10^13 cubic LY (roughly)

Mass of the galactic disk is of order 10^11 solar masses (possibly less, as the halo seems to have most of the mass).

Volume per solar mass ~100 cubic LY. Cube root of 100 CLY is 4.64 LY which is average edge of a "box" with one solar mass inside. If stars were evenly spaced they would therefore be about 4-5 LY apart. In fact, the average star is smaller than the Sun but even this would not change the result by more than a factor of 2.

So it is not surprising that the nearest star is currently about 4 LY away. Space is big.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

.

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