We revisit a central result of Muhly and Solel on operator algebras of C*-correspondences. We prove that (possibly non-injective) strongly Morita equivalent C*-correspondences have strongly Morita equivalent relative Cuntz-Pimsner C*-algebras. The same holds for strong Morita equivalence (in the sense of Blecher, Muhly and Paulsen) and strong ∆-equivalence (in the sense of Eleftherakis) for the related tensor algebras. In particular, we obtain stable isomorphism of the operator algebras when the equivalence is given by a σ-TRO. As an application we show that strong Morita equivalence coincides with strong ∆-equivalence for tensor algebras of aperiodic C*-correspondences.
IntroductionIntroduced by Rieffel in the 1970's [45,46], Morita theory provides an important equivalence relation between C*-algebras. In the past 25 years there have been fruitful extensions to cover more general (possibly nonselfadjoint) spaces of operators. These directions cover (dual) operator algebras and (dual) operator spaces, e.g. [3,4,6,7,[16][17][18][19][20][21][22]34]. There are two main streams in this endeavour. Blecher, Muhly and Paulsen [6] introduced a strong Morita equivalence SME ∼ , along with a Morita Theorem I, where the operator algebras A and B are symmetrically decomposed by two bimodules M and N , i.e. A ≃ M ⊗ B N and B ≃ N ⊗ A M. Morita Theorems II and III for SME ∼ were provided by Blecher [3]. On the other hand Eleftherakis [16] introduced a strong ∆-equivalence ∆ ∼ that is given by a generalized similarity under a TRO M , i.e. A ≃ M ⊗ B ⊗ M * and B ≃ M * ⊗ A ⊗ M. Although they coincide in the case of C*-algebras, relation ∆ ∼ is strictly stronger than relation SME ∼ . Indeed SME ∼ does not satisfy a Morita Theorem IV, even when X and Y are unital [6, Example 8.2]. However a Morita Theorem IV holds for ∆ ∼ on σ-unital operator algebras [19, Theorem 3.2].