Historical context: This article reflects reporting published on March 18, 2022. Names, positions, schedules, figures, and circumstances are presented as they were described at that time, not as a current update.

What is dark matter stars? Scientists arrived at the composition, by fitting a theoretical model of the universe’s makeup to the combined set of cosmological observations: 68 per cent dark energy, 27 per cent dark matter, and 5% normal matter. What is dark matter, exactly? We know a lot more about what dark matter isn’t than we do about what it is. For starters, it’s dark, which means it’s not visible in the form of stars and planets.

Observations demonstrate that the observable stuff in the cosmos is considerably too little to account for the 27 per cent required by the observations. Second, it isn’t in the form of ordinary matter, which is made up of particles known as baryons. We know this because the absorption of radiation travelling through baryonic clouds would allow us to detect them. Third, black matter is not antimatter because the distinctive gamma rays created when antimatter annihilates matter is not visible.

Finally, the number of gravitational lenses we find can rule out enormous galaxy-sized black holes. High concentrations of matter bend light travelling near them from things further away, but we don’t detect enough lensing events to suggest that such objects might account for the requisite 25% share of dark matter.