Japan builds ultra-precise X-ray telescope that spots a 3.5 mm dot from 1 km

A Japanese collaboration from Nagoya University and the SPring-8 facility has developed a high-resolution X-ray telescope with nanometer-precision, seamless nickel mirrors capable of resolving a 3.5 mm object at 1 km. Ground tests used a 10‑micrometer X-ray source about 900 meters away to simulate distant starlight, and the instrument flew on the FOXSI-4 sounding rocket in 2024 to observe a solar flare, validating its performance in space. The team plans a refined version for FOXSI-5 in 2026 and aims to miniaturize the optics for CubeSats to broaden access to high-resolution X-ray observations.