Dark Matter


Dark matter is a kind (possibly more than one) of matter hypothesized to account for gravitational effects that appear to be the result of invisible mass. In the early 1930s, astronomers Jan Oort and Fritz Zwicky postulated the existence of invisible masses to provide the additional gravity required to explain the observed stellar rotational speeds in the Milky Way galaxy. Later in the 20th century, more evidence emerged to support this hypothesis. Distant galaxies were found to form distorted or multiple images by invisible gravitational lenses. In cosmology, large-scale structures of the universe could not evolve into what we see today without dark matter dominating over the ordinary matter that forms stars and galaxies.

Moreover, the cosmic microwave background (CMB), the relic of the early universe resulted from the decoupling between radiation and matter at around 380,000 years after the Big Bang, cannot be fully explained unless there is 5.4 times as much ‘cold’ dark matter as ordinary matter.

One widely studied theory proposes that dark matter is composed of an as yet unobserved fundamental particle — unobserved because it interacts so weakly with our ordinary (Standard Model) particles, which is why it is ‘dark’. However, there many other ways to produce the effect attributed to dark matter. LeCosPA theorists have contributed to many of these alternates, including primordial black holes, imperfect fluid dark matter, etc.

Although there are strong evidences for the existence of dark matter, so far there has no detection of it. Efforts in search of dark matter can be categorized into direct, indirect, and collider searches. Direct search, which often invokes underground detectors, looks for the rare event that a passing dark matter particle interacts with an atom of ordinary matter. Indirect search looks for signatures resulting from dark annihilation, usually in astrophysical phenomena. Finally the collider search aims to create a dark matter particle from the collision of high-energy ordinary particles such as protons, similar to how the Higgs particle was recently discovered.