Dark matter is a type of matter that is predicted to make up most of the matter in the universe, yet it is very difficult to detect using conventional experimental techniques, as it does not emit, absorb, or reflect light. While some past studies gathered indirect hints of its existence, dark matter has never been directly observed; thus, its composition remains a mystery.
One hypothesis is that dark matter is made up of axionlike particles with an extremely low mass, broadly referred to as ultralight axionlike dark matter (ALDM). As these particles are exceedingly light, predictions suggest that they would behave more like waves than individual particles on a galactic scale.
The PPTA collaboration, a large team of researchers based at different institutes worldwide, applied a new approach to search for ALDM by cross-correlating polarization data of pulsars, neutron stars that spin rapidly and emit highly regular beams of radio waves. This approach, termed the “Pulsar Polarization Array (PPA),” entails measuring the polarization position angles of a series of pulsars and how they changed over time and with respect to pulsar spatial position.
