A proposed theory of gravity does away with dark matter, even as new astrophysical findings challenge the need for galaxies full of the invisible mystery particles.
Just months after their discovery, gravitational waves coming from the mergers of black holes are shaking up astrophysics.
A satellite spotted a burst of light just as gravitational waves rolled in from the collision of two black holes. Was the flash a cosmic coincidence, or do astrophysicists need to rethink what black holes can do?
The path from a revolutionary set of equations to the detection of gravitational waves was strewn with obstacles and controversy, explains the physicist Daniel Kennefick — and the struggle continues.
Ripples in space-time have been detected a century after Einstein predicted them, launching a new era in astronomy.