# N-body units

Quantity | Expression |
---|---|

Length (R) | |

Mass (M) |

**N-body units** are a completely self-contained system of units used for N-body simulations of self gravitating systems in astrophysics. In this system, the base physical units are chosen so that the total mass, *M*, the gravitational constant, *G*, and the virial radius, *R*, are normalised. The underlying assumption is that the system of N objects (stars) satisfies the virial theorem. The consequence of standard N-body units is that the velocity dispersion of the system is and that the dynamical -crossing- time scales as .
The first mention of standard N-body units was by Michel Hénon (1971).^{[1]}
They were taken up by Haldan Cohn (1979)^{[2]}
and later widely advertised and generalized by Douglas Heggie and Robert Mathieu (1986).^{[3]}

## References

- ↑ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1971Ap%26SS..14..151H&db_key=AST&data_type=HTML&format=&high=45c123dad007642
- ↑ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1979ApJ...234.1036C&db_key=AST&data_type=HTML&format=&high=439859188922689
- ↑ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1986LNP...267..233H&db_key=AST&data_type=HTML&format=&high=439859188922689