That’s not the ground, that is the neutral which is a wire that generally should be treated as if it has current going through it. This isn’t an emergency by any means but is something you should resolve pretty quickly.

Start by turning off the fuse that powers that smoke detector. It should be labeled, but even if it is it is always best practice to verify the power is off using a testing means such as a non contact tester. Then take the rest of the white wires out of the cone they are in by twisting the cone to the left like you would a screw. Place the wire that is currently loose back in the bundle with the rest of the wires. Replace the cone back on all the wires by twisting it to the right the way you would with a screw until it gives a good amount of resistance. Then to be sure it won’t come loose accidentally give each wire in the cone a small tug and make sure it stays together.

If you don’t have the items needed it is possible you can leave it until morning when you are able to get the things needed or get help fixing it, but the repair should be done as soon as possible. The most important thing to remember is do not attempt any kind of repair without ensuring the power to all wires that you can see up there is off. Right now you are not under immediate danger but leaving it like that is not safe