### Heggie-Hills law

**(Heggie's law, Heggie's theorem)**
(hard binary stars generally get harder when encountering a third star)

The **Heggie-Hills law** (i.e., **Heggie's law** or **Heggie's theorem**)
in stellar dynamics is:
hard binary stars tend to harden, and soft binaries soften,
i.e., given some distinction between small (hard) and large (soft)
orbits, encounters with third objects that affect the dynamics
tend on average to make such small orbits smaller and such large
orbits larger.

(*binary stars,dynamics,stars*)
http://vmsstreamer1.fnal.gov/VMS_Site_03/Lectures/Colloquium/presentations/060125Rasio.pdf

https://www.maths.ed.ac.uk/~heggie/lectures1+2.pdf

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