# Tag Info

A C*-algebra is a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = b* a* and the C*-identity ‖a* a‖ = ‖a‖². Related tags: (banach-algebras), (von-neumann-algebras), (operator-algebras), (spectral-theory).

A C*-algebra is a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = b*a* and the C*-identity ‖ a*a ‖ = ‖ a ‖2.

For bounded operators on a given Hilbert space, C*-algebras characterize topologically closed subalgebras of ${\mathcal B}({\mathcal H})$ (in operator norm), also closed under taking the adjoint operator. C*-algebras are at the heart of (non-commutative-geometry) and are extensively used in (mathematical-physics).