Noncommmutative Gelfand Duality for not necessarily unital $C^{\ast }$-algebras, Jordan Canonical form, and the existence of invariant subspaces

Gelfand-Naimark duality (Commutative $C^{\ast }$-algebras $\equiv$ Locally compact Hausdorff spaces) is extended to $C^{\ast }$-algebras $\equiv$ Quotient maps on locally compact Hausdorff spaces. Using this duality, we give for an \emph{arbitrary} bounded operator on a complex Hilbert space of several dimensions, a functional calculus and the existence theorem for nontrivial invariant subspace.