Board Thread:Warhammer 40k General Discussion/@comment-7186329-20130329201743/@comment-6078851-20130426012432

the power to blow up stars, while the tech probably originated from the c'tan, rests in necron hands. this tech, however, rests in the possesion of a particularly considerate necron.

all stars are linked to their neighbours via gravity, so if a star is destroyed, naturally or by design, then it affects the orbits of neighbouring stars - which affects the orbits of their neighbouring stars etc and so on. this could lead to a complete galactic destabilisation, so if one star is 'removed' then the entire neighbourhood has to be micromanaged (by the necrons) to prevent a terminal cascade.

this is the main reason why the 'considerate' necron won't use the celestial orrery, but (as far as i know) there is a war currently being fought over possesion of the celestial orrery, and if the 'inconsiderate' necrons win then stars start to 'pop', regardless of the collateral effect.