Dark energy is another enigmatic component of the universe, distinct from dark matter. It is thought to be responsible for the observed accelerated expansion of the universe. Unlike dark matter, which exerts gravitational attraction and tends to pull matter together, dark energy appears to have a repulsive effect, causing the expansion of the universe to accelerate over time.

The nature of dark energy is not well understood. One leading hypothesis is that it could be associated with the vacuum energy of empty space, sometimes referred to as the cosmological constant, originally introduced by Albert Einstein in his theory of general relativity. According to this theory, empty space itself possesses energy that drives the accelerated expansion of the universe.

Other theories suggest that dark energy may be a dynamic field, with its properties changing over time. Understanding dark energy is one of the key challenges in modern cosmology, as it holds profound implications for the fate and ultimate structure of the universe. Ongoing observational efforts, such as studies of distant supernovae and the cosmic microwave background radiation, aim to shed light on the nature of dark energy and its effects on the cosmos.