Would you need a power source? If you aim your ship correctly, then put everything alive into cryo, the ship could go completely dark, vent all heat and become a frozen rock. Then after [very long time] the ship enters the vicinity of a different star and can be reactivated and unfrozen using solar energy.
You dont need energy to maintain cryo if the whole ship is at 1° kelvin.
(Of course that relies on cryo sleep being possible)