WESTPORT — It’s unfathomable.

Even though “dark matter” comprises nearly 85 percent of the mass of the universe, according to the Westport Astronomical Society, no one is really certain what it is.

But one of the latest research efforts to unravel this celestial mystery will be detailed at a May 20 program, “The General Antiparticle Spectrometer: Hunting for Dark Matter from an Antarctic Balloon,” hosted by WAS.

The free presentation by Gabriel Lewis Bridges, a PhD candidate studying particle astrophysics at Columbia University, will take place at 8 p.m. Tuesday, May 20, at the society’s headquarters,  182 Bayberry Lane. The program also will be live-streamed via the group’s YouTube channel and Zoom.

Bridges will explain research using the General Antiparticle Spectrometer, or GAPS, a balloon-borne particle detector that was assembled at a station in Antarctica last winter. The equipment is expected to be launched this winter “to hunt low-energy anti-particles in cosmic rays,” WAS said.

Bridges became fascinated with science at a young age, “discovering video games through the NASA website and spending his Saturdays computing the entropy of plasma waves,” WAS said in announcing the program.