These objects are the Realm String, which marks the very center of the Realm, and also acts as a connection between the Realm and the Hub. The other thing is a Guardian. The Guardian is tasked with defending their Realm from any dangers it may face, as well as a sort of backup plan for other Realms. If the Guardian of one Realm needs help, one from another Realm can come and help defend the Realm in need. I happen to be the Guardian of my Realm, along with two others, as the Highest Realm is the center of the Realms, and if it falls, the rest are soon to follow. That's why it has three Guardians.
(Hope this wasn't too long)