Final answer:
Gravitational lensing is a phenomenon where a massive object, such as a galaxy or a galaxy cluster, bends the light from more distant objects, revealing the distribution of dark matter. Dark matter cannot be directly observed, but its presence and mass distribution can be inferred from the gravitational lensing effects. Through gravitational lensing studies, we have learned that dark matter makes up the majority of the mass in galaxies and galaxy clusters.
Step-by-step explanation:
Gravitational Lensing and Dark Matter
Gravitational lensing is a phenomenon that occurs when a massive object, like a galaxy or galaxy cluster, bends the light of more distant objects behind it.
This effect was predicted by Albert Einstein's general theory of relativity, which states that mass can warp the fabric of spacetime and, as a result, bend the path of light passing nearby.
The relevance of gravitational lensing to dark matter lies in its ability to reveal the presence and distribution of this elusive substance. While we cannot see dark matter directly, we can infer its existence through the gravitational lensing effect it has on distant starlight.
Dark matter makes up a significant portion of the total mass in galaxies and galaxy clusters, despite being invisible. Studies of gravitational lensing have shown that galaxy clusters can contain more than ten times as much dark matter as luminous matter. These clusters can bend the light from distant galaxies into streaks and arcs, allowing astronomers to create detailed maps of the dark matter's distribution.
In addition to galaxies, other potential gravitational lenses that have been considered are brown dwarfs and lone Jupiter-like planets. However, these have been ruled out as the primary constituents of dark matter. The gravitational lensing effects we observe are too extensive to be accounted for by these smaller objects alone.
Gravitational lensing is not just a tool for observing large-scale phenomena; it also plays a vital role in measuring the amount of dark matter in galaxy clusters. These measurements have generally agreed with those obtained from observing galaxy velocities and X-ray emissions, further validating the presence of dark matter.