China’s FAST Telescope Discovers Largest Known Atomic Gas Structure

An international team led by Xu Cong of the National Astronomical Observatory of China has recently used the advanced FAST telescope to observe compact galaxy group Stephan’s Quintet and its surrounding area, capturing images of an atomic gas system that extends for about 2 million light years, or 20 times larger than our Milky Way.

This is the largest atomic gas system ever detected in the universe, and the achievement was subsequently published in the international academic journal Nature on October 19. FAST stands for Five-hundred-meter Aperture Spherical Telescope, and is also known by its nickname “Tianyan” (天眼).

The picture above shows the distribution of atomic gas in the sky around Stephan’s Quintet, as detected by FAST. The thinner the red halo, the lower the density of the gas column.

Since it was discovered by French astronomer Édouard Stephan in 1877, Stephan’s Quintet is the most heavily studied compact galaxy group, and it has also become one of the first five targets observed by the James Webb Space Telescope and shown to the public for the first time. The background in the picture above is a color optical image obtained by the telescope, and Stephan’s Quintet is located in the middle. The embedded image is an infrared band color picture recently released by the James Webb Space Telescope: blue and white lights represent stellar radiation in the near infrared band, while orange and red lights represent gas and dust radiation in the mid-infrared band.

FAST’s latest discovery reveals the existence of a large-scale low-density atomic gas structure in outer space far from the center of the galaxy cluster. The formation of these gas structures is probably related to the history of intergalactic interactions during the early formation of Stephan’s Quintet, which has existed for about one billion years.

This discovery challenges the study of the evolution of galaxies and their gases in the universe, because it is difficult for existing theories to explain why these thin atomic gases have not been ionized by ultraviolet background radiation in space for such a long time. This observation by FAST indicates that there may be more such large-scale low-density atomic gas structures in the universe.

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Observing gas in the universe is a very important research topic in astrophysics, as the origin of all celestial bodies in the universe is related to atomic gas. For example, the main evolution process of galaxies is the process of continuously absorbing atomic gas from space and transforming it into stars. Radio astronomical bands can directly observe atomic gas in the universe.

FAST is a single-aperture radio telescope with the largest aperture and the highest sensitivity in the world. It can detect the dim radiation emitted by extremely thin dispersed atomic gas far away from the center of galaxies, opening up a new window to study the origin of celestial bodies.

Aerial photo taken on March 28, 2021 shows China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST) under maintenance in southwest China’s Guizhou Province. (Source: Xinhua)