What are gravitational waves?

Gravitational waves are indeed ripples in spacetime that are generated by the acceleration of massive objects, particularly in extreme situations, such as when two black holes merge or neutron stars collide. These waves are a fundamental prediction of Einstein's General Theory of Relativity, which describes how massive objects influence the geometry of spacetime around them.

As these massive objects accelerate — for instance, during mergers — they disturb the surrounding spacetime, creating waves that propagate outward at the speed of light. This process is akin to how a stone thrown into a pond creates ripples on the surface of the water. When these gravitational waves reach Earth, they cause incredibly tiny distortions in length, which can be detected by highly sensitive instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory).

In contrast, the other options do not accurately describe gravitational waves. The first option describes a general motion of celestial bodies rather than the specific mechanics of gravitational waves. The third option refers to phenomena associated with solar radiation and planetary atmospheres, which are unrelated to gravitational waves. Lastly, the fourth option discusses light waves emitted from galaxies, while gravitational waves are fundamentally different entities, associated with the curvature of spacetime rather than electromagnetic radiation.