WHAT COULD DARK MATTER BE?

PRIMORDIAL BLACK HOLES

Imagine the mass of the Earth crammed into a space the size of your thumbnail. Many cosmologists believe the early Universe spawned reams of these tiny black holes, the combined gravitational pull of which could account for dark matter.

WIMPs (WEAKLY INTERACTING MASSIVE PARTICLES)

Once the most popular candidate, years of empty searches are starting to focus attention elsewhere. WIMPs came from an idea called supersymmetry, in which every currently known particle – such as the electron – has a heavier mirror image.

SUB-GEV DARK MATTER

Unlike primordial black holes and WIMPs, these particles would be up to a million times lighter than a proton. A new experiment to try and detect them – SENSEI – is currently being tested at Fermilab in the USA.

AXIONS

The excess of electrons discovered at the XENON1T experiment could point towards these dark matter particles streaming out of the Sun. They were first devised by particle physicists to plug a hole in our understanding of the strong nuclear force.

DARK BOSONS

The lightest of the major dark matter candidates. Evidence is mounting up for their existence from ground-based atomic experiments, along with black hole and gravitational wave astronomy. They could coalesce to form invisible boson stars.