N-body units

Quantity	Expression
Unit of length (R)	${\displaystyle {\frac {1}{R}}={\frac {1}{M^{2}}}\sum _{i,j\neq i}^{N}{\frac {m_{i}m_{j}}{\left|{\vec {r_{j}}}-{\vec {r_{i}}}\right|}}}$
Unit of mass (M)	${\displaystyle M=\sum _{i=1}^{N}m_{i}}$

N-body units are a completely self-contained

. The consequence of standard N-body units is that the velocity dispersion of the system, v, is ${\displaystyle \scriptstyle {\frac {1}{2}}{\sqrt {2}}}$ and that the dynamical or crossing time, t, is ${\displaystyle \scriptstyle 2{\sqrt {2}}}$. The use of standard N-body units was advocated by Michel Hénon in 1971.^[1] Early adopters of this system of units included H. Cohn in 1979^[2] and D. Heggie and R. Mathieu in 1986.^[3] At the conference MODEST14 in 2014, D. Heggie proposed that the community abandon the name "N-body units" and replace it with the name "Hénon units" to commemorate the originator.^[4]

References

External links

• N-Body Units
• STELLAR DYNAMICS by D.C. Heggie, p.6–7