"China's Sky Eye", seeing farther stars (self-reliance and self-improvement in science and technology)

Source: People's Daily

My scientists discovered the largest atomic gas structure in the universe at present

"China's Sky Eye", seeing farther stars (self-reliance and self-improvement in science and technology)

The picture shows the distribution of atomic gas in the celestial region around the compact galaxy group "Stephen Quintuplex Galaxy" detected by the "Chinese Sky Eye".

Photo courtesy of the National Astronomical Observatory of the Chinese Academy of Sciences

Core reading

The origin of all celestial bodies in the universe is inseparable from atomic gas. Recently, our scientists used the "Chinese Sky Eye" to discover an atomic gas structure with a scale of about 2 million light years, which is the largest atomic gas structure detected in the universe at present. The "Chinese Sky Eye" has also become the only telescope that can detect such thin gas.

Using the "Chinese Sky Eye", an international team led by Xu Cong, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, has discovered a huge atomic gas structure with a scale of about 2 million light years, located in the famous compact galaxy group "Stephen Quintuple Galaxy", which is 20 times larger than the Milky Way and is the largest atomic gas structure detected in the universe so far. On October 19, the results were published in the international academic journal Nature.

The origin of cosmic celestial bodies is inseparable from atomic gases

A very important study in astrophysics is the observation of gases in the universe. The origin of all celestial bodies in the universe is inseparable from atomic gas. For example, the main evolutionary process of galaxies is to continuously absorb atomic gas from space and then convert it into stars.

Cheng Cheng, one of the team members and a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, said: "All the celestial objects we see, such as stars, will eventually come down to neutral atomic hydrogen gas. ”

In addition, it is very important to study the gas itself. In this regard, Cheng Cheng further explained: "For example, when some stars form, they do not come from atomic hydrogen, but from molecular hydrogen. So, how does atomic hydrogen become molecular hydrogen? Why is the density of molecular hydrogen getting higher and higher? Also, how do these baryonic materials such as atomic hydrogen converge in the central region of the galaxy, and then gradually form stars and become galaxies? These questions are critical to the study of various stages of celestial evolution. ”

Through radio astronomy, astronomers are able to make direct observations of atomic gases in the universe. The "China Sky Eye" is the world's largest and most sensitive single-aperture radio telescope, which has ultra-high sensitivity and can detect the faint radiation emitted by extremely thin dispersed atomic gases far from the center of the galaxy.

After research and analysis, the research team finally selected the famous compact galaxy group "Stephen quintuple galaxy" for observation. Since its discovery by French astronomer Stephen in 1877, the "Stephen quintuple galaxy" has been the most concerned group of galaxies in the field of astronomy, and has become one of the first five targets observed by the Webb Space Telescope and first shown to the public.

Cheng Cheng said: "Previously, telescopes in other countries have observed this galaxy group region many times, but the sensitivity of those telescopes is not high enough, so the observation results are not ideal. We expect to push the limits of previous observations. ”

The Chinese Sky Eye is the only telescope that can detect such thin gas

The interaction of galaxies in the universe and the source of the gas between them has always been an important issue in astronomy, and the "Chinese Sky Eye" is a "sharp weapon" to study this problem.

The international team led by Xu Cong, mainly the South American Astronomy Research Center of the Chinese Academy of Sciences, includes first-class infrared and radio astronomy experts at home and abroad, all of whom have rich experience in multi-band research. In the first quarter of the opening of the "China Sky Eye" to the international astronomical community, the team submitted an observation application and was awarded the observation time through the review.

Xu Cong said: "Our scientific goal is to take the 'Chinese Sky Eye' to the extreme, detect the thinnest gas in the universe, and study where the gas in galaxies comes from as far as the universe." ”

In astronomical observations, noise is inevitable. In order to achieve the observation goal, the debuggers of the "China Sky Eye" continued to improve, improve the sensitivity of the "China Sky Eye" and suppress noise, and finally adjusted its sensitivity to the limit in October 2021, successfully observing the extremely thin gas around the "Stephen Quintuple Galaxy".

Cheng Cheng said: "The before and after observations only took about a month, and the total exposure time of the telescope was 22 hours. This time can be said to be exceptionally fast, exceeding our expectations. ”

In this observation, the receiver of the "China Sky Eye" also performed particularly well.

"When the receiver receives the signal, it is a bit like a radio tuner, and the neutral hydrogen radiation we want is exactly around 1.39GHz, and we need to find a signal near this frequency band." Some telescope receivers have a narrow frequency band, but the 'China Sky Eye' receiver receives a wide frequency coverage and is very efficient. ”

To the surprise of the research team, these gases extended to 2 million light-years outside the galaxy, making them the largest atomic gas structure in the universe ever observed astronomically observed, and the "Chinese Sky Eye" became the only telescope that could detect such thin gas.

Challenges to study the evolution of galaxies and their gases in the universe

The latest discovery of the "Chinese Sky Eye" reveals the existence of large-scale, low-density atomic gas structures in the outer space far from the center of the galaxy group.

Xu Cong said: "The formation of these atomic gas structures is likely related to the history of intergalactic interactions during the early formation of the 'Stephen quintuple galaxy', which may have existed for about 1 billion years. ”

Cheng Cheng told reporters that such neutral atomic hydrogen dispersion systems have been observed before, but there is a neutral atomic hydrogen structure system near a galaxy, shaped like a tail. "Our original expectation was to use the diffusion distribution of neutral atoms of hydrogen to understand the history of galaxy group mergers. We had imagined that perhaps some neutral hydrogen was flung out to the edge of the galaxy, but when we saw such a large atomic gas structure on the outer edge of the galaxy, we speculated that there might be a galaxy whose neutral atomic hydrogen had been completely stripped out. Cheng Cheng said.

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

The operation of the "Chinese Sky Eye" has opened a new window for studying the origin of celestial bodies in the universe, and the results of this observation can be used to explore more ultraviolet background radiation ionization.