[More recent work has seen pulsar timing arrays (PTAs) such as NANOGrav successfully identify a specific flavor of gravitational wave known as the stochastic gravitational wave background (SGWB). The SGWB is similar in concept to the cosmic microwave background—a consistent glow from the early universe that astronomers can see as a series of microwaves coming from all directions at once.]

First time I've heard of this concept.