  The gravitational wave window onto the universe is expected to open in ~ 5
years, when ground-based detectors make the first detections in the
high-frequency regime. Gravitational waves are ripples in spacetime produced by
the motions of massive objects such as black holes and neutron stars. Since the
universe is nearly transparent to gravitational waves, these signals carry
direct information about their sources - such as masses, spins, luminosity
distances, and orbital parameters - through dense, obscured regions across
cosmic time. This article explores gravitational waves as cosmic messengers,
highlighting key sources, detection methods, and the astrophysical payoffs
across the gravitational wave spectrum.
