China's FAST telescope reveals unprecedented details of Milky Way

The vast space between billions of stars in the Milky Way is not empty, but filled with thin interstellar medium.

Using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), or the "China Sky Eye," Chinese scientists revealed the unprecedented details of the Galactic interstellar medium.

Led by Han Jinlin, a scientist with the National Astronomical Observatories of China, the research team published their new findings Saturday in the latest journal Science China: Physics, Mechanics & Astronomy.

According to Han, during the sensitive survey for pulsars using the FAST, the spectral line data of the interstellar medium was recorded simultaneously. Though the fine calibration is still underway, the results available are already the most sensitive for detecting neutral hydrogen gas clouds to date, showing unprecedented details about the distribution of neutral hydrogen gas.

Compared to all previous surveys, the improvement in angular resolution and sensitivity in the survey conducted by Han's team is "impressive," said John M. Dickey, emeritus professor with the University of Tasmania in Australia and the University of Minnesota in the United States, adding that the results are worthy of international attention.

The research team has also revealed the luminous regions ionized by bright stars and the diffuse ionized gas of unknown origin.

"Large single-dish telescopes such as the FAST are the best to probe the diffuse ionized gas," said Dana S. Balser, a scientist with the National Radio Astronomy Observatory in the United States.

For scientists worldwide, the Galactic magnetic fields which permeate the interstellar medium are extremely difficult to measure. The research team relied on the sensitivity of FAST to measure the Faraday effect of a large number of faint pulsars and revealed the Galactic magnetic fields in a much wider range in the Galactic disk and halo.

"Without FAST, the interstellar magnetic field in such a wide region would never be detected," Han said.

Characterized by high sensitivity, high spectral resolution, and high spatial resolution, the spectral line data is an extremely valuable resource for studying the structure of the Milky Way Galaxy and the interstellar ecological cycle, he added.

"The sensitive FAST observations can reveal unprecedented details of the Milky Way," said Jing Yipeng, an academician with the Chinese Academy of Sciences and professor at Shanghai Jiao Tong University.

"The databases of neutral hydrogen and ionized hydrogen published by these papers are valuable resources for astronomers over the world," Jing added.

Located in a naturally deep and round karst depression in southwest China's Guizhou Province, FAST started formal operation in January 2020 and officially opened to the world on March 31, 2021. It is believed to be the world's most sensitive radio telescope.