difference between Pub/Sub and observer pattern

The purpose of the Publish/Subscribe pattern is the same as the Observer pattern: you want to notify other services when certain events take place. But there is an important difference between the Observer and Pub/Sub patterns. In the observer pattern, the broadcast is performed directly from the observable to the observers, so they "know" each other. But when using a Pub/Sub pattern, there is a third component, called broker, or message broker or event bus, which is known by both the publisher and subscriber. Therefore, when using the Pub/Sub pattern the publisher and the subscribers are precisely decoupled thanks to the mentioned event bus or message broker.