Swihart 10-1

reaching behavior v propto 1/sqrt(r), indicates further increases in r
encloses no additional mass, so 100 kLY is the radius.

the mass:
v^2/r=GM(r)/r^2
v^2 r/G=M(r)   !see here that v propto 1/sqrt(r) means M(r) does not depend on r

* let r=1e5*LY
* ? (240e3)^2*r/Gn
    .8164818306494901E+42
* ? res/Msun
    410606005918.8376    !4e11 Msun