An international collaboration of physicists has observed the black hole Cygnus X-1 using a balloon-borne telescope, aiming to study the mechanisms of energy release as matter falls into the black hole. This balloon telescope observation project provides new data for understanding the physical environment surrounding black holes.

The researchers measured X-ray polarization signals from the black hole using the balloon-borne telescope XL-Calibur. Professor Henric Krawczynski of the Department of Physics at Washington University stated: "The observations we have made will be used to test increasingly realistic and state-of-the-art computer simulations of the physical processes occurring near black holes." The balloon telescope flew from Sweden to Canada in July 2024, during which it collected observational data.

The research team published their observational results on Cygnus X-1 in The Astrophysical Journal, including the most precise measurement to date of the hard X-ray polarization of this black hole. Graduate student Efrem Gao, who participated in the project, pointed out: "When we cannot take ordinary photographs from Earth, polarization imaging is very useful for understanding what is happening around black holes." These balloon telescope observation data will be combined with data from other satellites to advance our understanding of the physical properties of black holes.

The XL-Calibur balloon telescope project involved more than ten research institutions, including Washington University and the Japan Aerospace Exploration Agency (JAXA). The team plans to conduct a new round of observations from Antarctica in 2027, which is expected to detect more black holes and neutron star targets.