relay In a circuit being switched by an NPN transistor do power supply and input need the same ground

Make a circuit that will allow me to switch on a relay that will turn on an LED. However, the relay is rated for 12 V, and I only have an input of 5 V, so I`m using an NPN transistor. to switch the power to the relay on and off. Here`s the schematic: If my 12 V power supply is 8 AA batteries (not sustainable, but I`m just using it for testing), how would I connect that to the same ground as the arduino, instead of the negative side of the batteries

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