Binary-Binary Interactions and the Formation of the PSR B1620-26 Triple System in M4

The hierarchical triple system containing the millisecond pulsar PSR B1620-26 in M4 is the first triple star system ever detected in a globular cluster. Such systems should form in globular clusters as a result of dynamical interactions between binaries. We propose that the triple system containing PSR B1620-26 formed through an exchange interaction between a wide primordial binary and a {\it pre-existing/} binary millisecond pulsar. This scenario would have the advantage of reconciling the $\sim {10}^9$yr timing age of the pulsar with the much shorter lifetime of the triple system in the core of M4.