Everyone on Earth is familiar with gravity to some extent; it is the force that pulls us down to the planet’s surface. In fact, all objects with mass tug on other objects moving around them because of gravity. The strength of the gravitational pull depends on the mass of the object, and is often too weak to notice. However, for things as massive as galaxies, scientists can study the make-up of the its matter by its gravitational influence on surrounding astronomical objects like stars.
Several experiments, such as the Dark Energy Survey (DES) in Chile, use gravity to search for new, fundamental particles that constitute dark matter. Normal matter—things made of atoms, such as planets and stars—reflect light and can therefore be observed with telescopes. However, several observations have indicated that there is more matter dispersed through galaxies than is seen. We call this invisible mass dark matter since it cannot reflect light. Gravitational effects are only way we can detect its presence. Although dark matter does not scatter light, its gravitational pull can still bend the path of light. This effect, called gravitational lensing, can cause distorted or multiple images of the same object to appear. The DES uses a sophisticated telescope to observe gravitational lensing on objects up to 14 billion light years away which theorists use to hypothesize the dark matter distribution of the universe.
Measurements taken by DES and similar experiments provide important insight to both astronomy and particle physics. Scientists can work backwards from observing the lensing effect to deduce the mass of the invisible object causing the lensing. After measuring the mass, scientists build theories that fit the observations. Although studying the gravitational interactions of dark matter signifies its existence, it cannot directly explain the particle properties. The characteristics of dark matter particles remains an exciting open question in physics.
Managing Correspondent: Cari Cesarotti
Original Article: Gravitational Lenses – Symmetry Magazine
Image Credit: Galaxies SDSSCGB 8842.3 and SDSSCGB 8842.4, NASA & ESA