Intensity Interferometry Advances Astrophysical Studies with Third Order Correlation Measurements

Astronomical interferometry relies on combining light from multiple telescopes to reveal fine details of celestial objects, and a crucial aspect of this technique is measuring the relationships between light waves. Andreas Zmija, Gisela Anton, and Christopher Ingenhuett, along with colleagues Alison Mitchell, Prasenjit Saha, and Pedro Silva Batista, have now achieved a significant breakthrough by recording the first third-order correlations from astrophysical sources.

The team successfully isolates these subtle signals using the H. E. S. S. intensity interferometer, observing the stellar systems Nunki and Dschubba, and demonstrating a method to extract information previously inaccessible to intensity interferometry. While current sensitivity limits prevent full reconstruction of object geometries, this work establishes a vital pathway towards measuring the closure phase, a key parameter for detailed astronomical imaging, and validates the technique with a laboratory experiment using a pseudo-thermal light source. Researchers have now achieved a significant breakthrough by recording the first third-order correlations from astrophysical sources, successfully isolating these subtle signals using the H. intensity interferometer while observing the stellar systems Nunki and Dschubba. This work establishes a vital pathway towards measuring the closure phase, a key parameter for detailed astronomical imaging, and validates the technique with a laboratory experiment using a pseudo-thermal light source. Third-Order Correlations Reveal Interferometric Phases This study pioneered the first measurements of third-order correlation functions in astronomical sources, a crucial step towards recovering interferometric phases inaccessible to conventional intensity interferometry. Researchers employed the H. intensity interferometer, utilizing three of its 12-meter diameter telescopes to observe the stellar systems Nunki and Dschubba. This work directly addresses a long-standing limitation of intensity interferometry, its inability to measure phase information, which hinders detailed reconstruction of observed objects. To isolate the signal indicative of the cosine of the closure phase, the team developed a novel analysis technique to separate contributions from three-photon correlations from the dominant two-photon signals. The experiment harnessed simultaneous measurements from the three telescopes, enabling the computation of third-order correlations and the subsequent extraction of the closure phase information. While the current data lacked the sensitivity to definitively constrain closure phase values, the study successfully demonstrated the feasibility of this approach. To validate the analysis pipeline and confirm its effectiveness, researchers conducted a parallel laboratory experiment using a pseudo-thermal light source and the H. This controlled environment allowed for precise verification of the method and confirmed its ability to accurately extract the cosine of the closure phase, paving the way for future observations with improved sensitivity using larger telescope arrays. Third-Order Correlations Reveal Stellar System Geometry This work presents the first measurements of third-order correlations obtained using the H. intensity interferometer, observing the stellar systems Nunki and Dschubba in 2023. These measurements are crucial for accessing interferometric phases otherwise inaccessible with intensity interferometry, a technique rapidly gaining prominence in astronomical observation. Scientists successfully isolated the contribution of the third-order correlation term from the more dominant two-order correlations, a necessary step towards determining the closure phase, a key parameter for reconstructing the geometries of observed objects. Computation of the three-photon correlations required significant computational resources, utilizing a high-performance computing cluster, and taking considerably longer than the data acquisition itself. The resulting measurements reveal characteristic features, demonstrating the successful isolation of the third-order term.

The team developed a procedure to access the closure phase, paving the way for future intensity interferometers to utilize time-tagging of single photons to reduce computation time and enable real-time measurements.

Closure Phase Measurement With Intensity Interferometry This research presents the first measurements of third-order correlation functions, extending the capabilities of intensity interferometry beyond traditional two-point correlations. These measurements are crucial for accessing interferometric phases, and scientists successfully isolated the contribution of the third-order correlation term, a necessary step towards determining the closure phase. This work has the potential to significantly improve the quality of astronomical images, especially for complex sources, and could lead to new discoveries about the structure and evolution of stars and galaxies. 👉 More information 🗞 Towards measuring astrophysical third order correlation functions with the H.E.S.S. optical intensity interferometer 🧠 ArXiv: https://arxiv.org/abs/2512.13485 Tags: