Jonathan O’Callaghan in Quanta:
The discovery, announced today, shows that extra-large ripples in space-time are constantly squashing and changing the shape of space. These gravitational waves are cousins to the echoes from black hole collisions first picked up by the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment in 2015. But whereas LIGO’s waves might vibrate a few hundred times a second, it might take years or decades for a single one of these gravitational waves to pass by at the speed of light.
The finding has opened a wholly new window on the universe, one that promises to reveal previously hidden phenomena such as the cosmic whirling of black holes that have the mass of billions of suns, or possibly even more exotic (and still hypothetical) celestial specters.
More here.