Listening for molecules between the stars
High in the mountains of Nagano Prefecture, at an altitude of 1,350 meters, is one of the world's most sensitive instruments for cosmic chemistry: the Nobeyama Radio Observatory (NRO). The site's elevation and dry climate minimize atmospheric water vapor, which would otherwise absorb the faint millimeter-wavelength radio signals from deep space. The observatory's main instrument is a massive 45-meter single-dish radio telescope, which began operations in 1982.
At the time of its completion, it was the largest radio telescope of its kind, designed specifically to detect radiation in the millimeter band (1mm to 10mm wavelengths). This part of the electromagnetic spectrum is emitted by the cold, dense molecular clouds where stars and planets are born. The 700-ton telescope has a surface precision of 0.1 millimeters, allowing it to efficiently collect these high-frequency signals. Its design uses a principle called homologous deformation, where gravity pulls on the structure in a predictable way, ensuring the dish maintains a perfect parabolic shape as it moves to track objects across the sky.
A catalog of cosmic chemistry
The Nobeyama 45-m telescope has made significant contributions to astrochemistry, the study of molecules in space. It excels at detecting the spectral-line emissions from molecular gases, revealing their composition, mass, and motion. This capability led to significant work in mapping the distribution of organic molecules in interstellar space.
Scientists have used the telescope to study large molecular clouds, including Sagittarius B2, located near the center of the Milky Way. In these observations, they identified significant quantities of acetonitrile (CH3CN), an organic molecule considered a tracer for more complex organic matter. Discoveries like this provide strong evidence that the chemical precursors to life are not unique to our solar system but are common throughout the galaxy. The observatory's research also provided early, compelling evidence for the existence of a supermassive black hole at the center of our galaxy.
The site historically operated the Nobeyama Millimeter Array, a set of six 10-meter antennas that worked together as an interferometer. This array could produce images with a spatial resolution equivalent to a single telescope 600 meters in diameter. The observatory also runs a Nobeyama Radioheliograph, a dedicated array of eighty-four 80-cm antennas that continuously monitors the Sun.