Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 320 4 b Solution Created 2026-10-03 Updated 2026-10-06
False as a claimed change between isolated steady endpoints. Conservation of energy by itself would allow a more negative and a larger , but both endpoints must also obey the virial theorem. For a finite isolated equilibrium with no surface term,If total is conserved between the two equilibria, the fixed-energy virial constraint between steady states givesThis includes both ordered rotation and random stellar motion. A galactic bar or other instability can redistribute angular momentum and concentrate a central component, but compensating expansion or rearrangement elsewhere must preserve the global energy constraint. Central concentration alone does not prove that the whole system has a more negative .
A remnant could have different energies if stars escape, or if an external component exchanges energy with it; then the conserved total energy would include that other component. Those cases do not justify treating the bound disc simultaneously as a closed fixed-energy system and as a new equilibrium with increased .