Dyson Spheres around White Dwarfs

[selden]

A related paper:

Gaia Reveals Evidence for Merged White Dwarfs
Mukremin Kilic, N. C. Hambly, P. Bergeron, C. Genest-Beaulieu, N. Rowell

https://arxiv.org/abs/1805.01227

We use Gaia Data Release 2 to identify 13,928 white dwarfs within 100 pc of the Sun.

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If my arithmetic is right, that means that at least 2% of all stars are White Dwarfs, so there are lots of them available. Actually, the percentage probably is somewhat higher, since the efficiency of detecting stars, especially those as dim as white dwarfs, falls off with distance.
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Here's my arithmetic:

volume with a radius of 100pc:  4/3 *pi* 100^3 = 4 186 667 cubic pc
14000/4200000 = 0.0033 wd / cubic pc

Using the "traditional" value for the density of stars in the solar vicinity, if the average star density is 0.14 stars / cubic pc, then 0.0033/0.14 = 0.024 or 2.4% of stars are White Dwarfs.

To check that number:
if the average star density is 0.14 stars / cubic pc, then there are
0.14*4/3*pi*100^3 = 580,000 stars within 100 pc. 14000/580000 = 0.024 = 2.4%

However, Gaia yields a slightly higher stellar density within 100 pc: about 0.167 stars/cubic pc.

When I queried the Gaia archive for a list of stars with a parallax > 10 milli-arc seconds (i.e. with distances < 100 pc) it returned a row count of 700,055. (I didn't put any constraint on the parallax accuracy, though.)  Gaia has been reported as detecting ~2x as many stars as were originally expected, so a count of 700,000 instead of 600,000 doesn't seem too unreasonable.

So 14000/700000 = 2%.

and 700000/4200000 = 0.167 stars / cubic pc.