Core points:
Stephen’s five-stack galaxy has roughly the same redshift, while the other galaxy’s redshift is much smaller than the other four. In the two-dimensional space of the sky, these five galaxies are together. But in three-dimensional space, there are actually only four galaxies together, and the other is actually very far away from them, and it is a prospective galaxy.
In Stephen’s quintuple galaxy, there is an shock wave with a size of about 100,000 light years, which is the largest shock wave that exists between the two Milky Way galaxies.
"China Sky Eye" FAST is the largest single-diameter radio telescope with the highest caliber and the highest sensitivity. With its observation of hydrogen atom gas, the formation and development history of celestial bodies can be further studied.
The discovery of the largest and low-density hydrogen atomic gas structure to date by Xu Cong’s team may have a significant or even subversive impact on the traditional understanding of galaxies.
Recently, an international team led by Xu Cong, a researcher at the National Observatory of the Chinese Academy of Sciences, used the "China Sky Eye" FAST to image and observe hydrogen atomic gas in the dense galaxy group Stephen's five-fold galaxy and surrounding sky areas, and discovered a huge and thin atomic gas structure with a scale of about 2 million light years. This is the largest atomic gas structure detected in the universe so far.
What are the characteristics of Stephen’s Five-fold Galaxy? Why is it attracting much attention from astronomical research? Where is the strength of the "Chinese Sky Eye" FAST in astronomical observations? Why do we need to study hydrogen atomic gases? What impact will this discovery have? Beijing News Broadcast hosts Duan Yulong and Xu Cong will answer you!
Special low redshift: Stephen’s Five-layer Galaxy
has triggered huge debate in the astronomical world
Duan Yulong: What are the characteristics of Stephen’s Five-layer Galaxy? Why should we study it?
Xu Cong: Stephen’s Five-layer Galaxy is the first to be discovered in galaxy groups. It was discovered by French astronomer Edward Stephen in 1877.
We now know that these five nebula are actually five galaxies, and the regression speed of four galaxies is roughly the same. The Hubble regression rate of another galaxy is about ten times different from that of the other four galaxies.
In astronomy, there is a term that defines this Hubble regression speed as a redshift. This is a bit like Doppler effect . When an object leaves us, the wavelength of light emitted from it will move towards the red end, so it is called red shift. The ten times redshift difference between
indicates that this galaxy and the other four galaxies are not actually on the same redshift. According to the Big Bang theory, redshift is proportional to the distance, which also shows that this galaxy is not at the same distance as the other four galaxies.
So, in the two-dimensional space of the sky, these five galaxies are together. But in three-dimensional space, there are actually only four galaxies together, and the other is actually very far away from them. It is a foreground galaxy, which is much smaller than the other four galaxies.
Stephen's Five-Story Galaxy photographed by Hubble Space Telescope (Photo source: NASA, ESA, CSA, STScI)
This matter has now become a conclusion, but this statement was seriously challenged by in the 1960s. The challenger was a very famous astronomical master at the time. One of their common points is that does not believe in the Big Bang theory , but believes in the eternal universe and the uniform universe.
For example, Fred Hoyle, who served as the president of , the famous British astronomer Jeffrey Ronald Burbitch, etc. Hoyle nearly won the Nobel Prize in Physics in 1983 . The leading figure at that time was called "Qiju" Alp, who was the author of the very famous "Alp Special Galaxy Table".
And in the 1960s, quasar just happened to be discovered. These quasars all have very large redshifts and look very bright. So, if we follow the Big Bang theory, their big redshift means that they are far away from us.Their brightness means that their luminosity is very strong.
Duan Yulong: With such a bright light, what is its energy? Where does its energy come from?
Xu Cong: Now we know that the energy of a quasar is caused by the accretion of matter by the central black hole.
But at that time, this theory was not widely accepted. Alp has his own theory, that is, the red shift of the quasar has nothing to do with distance, and he does not recognize the Big Bang theory. He believes that quasar is a mass of special matter ejected from the middle of the galaxy nucleus. The big redshift itself is a special property of it, and this redshift will become smaller and smaller as the mass of matter grows older.
What is Alp's explanation for the low-redshift galaxy in Stephen's quintet? He said that this galaxy ejected special matter from the galaxy nucleus of another galaxy, and it is now very old, so its redshift is quite small.
Because of this so-called "non-cosmic redshift" hypothesis, the Stephen Five-Galaxy was very attractive to astronomers of both schools of both sides around the 1960s, and attracted widespread attention from everyone.
The largest shock wave that has been discovered so far: Stephen’s Five-layer Galaxy
The “charm” that attracted the attention of the astronomical community
Xu Cong: In the 1980s, Stephen’s Five-layer Galaxy suddenly became “red” again. Because a Dutch astronomer Rong Allen discovered that has a very large shock wave in the Stephen quadripolar galaxy. The size of this shock wave is about 100,000 light-years, which is as big as the size of two Milky Ways. Until now, this shock wave is still the largest shock wave that has been proven between galaxies. A shock wave like is very, very rare in the neighboring universe, and should be more common in the early universe.
Stephen's Five-Story Galaxy photographed by Webb Space Telescope (Photo source: NASA, ESA, CSA, STScI)
Shock itself can tell us a lot of things. For example, the properties of gas, where does the gas come from, and whether it is possible for gas to produce stars in the future... If such shock waves often appear in the early universe, then we want to understand what impact it will have on the evolution and formation of this galaxy.
There is no such shock waves seen elsewhere, and the Stephen Five-Galaxy provides a very good laboratory to study these shock waves. Therefore, Stephen's Five-layer Galaxy has attracted great attention since then.
Large diameter and high sensitivity:
"China Sky Eye" FAST's "profit" in observation
Duan Yulong: It is precisely because the relevant signals emitted when the shock wave phenomenon occurs can be observed in FAST telescope , so do we use FAST telescope to observe Stephen's five-fold galaxy?
Xu Cong: is not yet. Speaking of radio bands, there are actually two types of radio waves that we want to study. One is the so-called continuous spectrum radio wave, which can directly detect the shock wave is the continuous spectrum radio wave.
continuous spectrum radio waves are often caused by synchronous acceleration radiation. To have synchronous acceleration radiation, there must be relativistic electrons. The shock wave will produce such relativistic electrons; and then there must be an electromagnetic field. Relativistic high-energy electrons will produce synchronous acceleration radiation when operating in a magnetic field.
There is also a kind of light wave, which is not emitted continuously in the radio band, but is a ray with very narrow bands.
The hydrogen atom has a very bright ray in the radio band, which is a 21 cm ray. This 21 cm ray is the brightest for hydrogen atoms. It is also the most important means for us to study atomic gases, that is, to observe this 21 cm radiation of hydrogen atomic ray in the radio band.
and FAST is very sensitive in this band.
National Observatory FAST Observation Base (Photo source: Official website of the National Observatory of Chinese Academy of Sciences)
In addition, FAST now installs a receiver called 19 beam. The so-called 19 beam means that there are 19 detectors on one receiver , which can point to 19 different points in the sky at the same time.Therefore, it is very efficient to use a 19-wave speed detector to image and observe hydrogen atomic radiation.
Because it is both sensitive and efficient, it took only 22 hours to achieve deep coverage of a sky area with a diameter of about 30 angular minutes. What is the concept of
30? It is almost a sky area as big as a full moon. Such an experiment, if used to observe it with previous equipment, usually takes several months to complete.
From shock wave to celestial body formation evolution:
The necessary and important research on hydrogen atomic gas observation and research
Duo Yulong: Why do we observe hydrogen atomic gas in that place? What conclusions were drawn through observations?
Xu Cong: First of all, why do we observe hydrogen atomic gas? Because we just said that we want to study shock waves, but to study shock waves in , we must know how shock waves are formed and the initial conditions when they are formed.
These initial conditions and the situation at that time, is related to the formation and development history of Stephen's Five-fold Galaxy.
National Observatory FAST Observation Base (Photo source: Official website of the National Observatory of Chinese Academy of Sciences)
Why can the distribution and movement of hydrogen atoms provide such information? Because hydrogen atoms are relatively loose inside and outside the galaxy. hydrogen atoms are relatively thin, unlike other things, such as stars, which are very heavy, so it is not easy to move them. When two galaxies interact, the first thing that is disturbed is these hydrogen atomic gases.
If we now detect these thin hydrogen atomic gases around Stephen’s quintet Galaxy, we can get the history of the early interactions of this galaxy group . Because these history can be reflected in these structures, motion, distribution and velocity fields.
Then we think, if we take this data and input it into our simulation calculation model, our simulation calculation will be more accurate. This was the idea at that time, so we submitted the observation report and obtained the observation time.
subverts traditional observation results:
Large-scale low-density gas structure exists around galaxies
segment Yulong : What is the final result of this observation?
Xu Cong: The results we published in the magazine " Nature " this time, we found that a hydrogen atom structure of about two million light years is far away from the center of Stephen's five-story galaxy, and the gas in this structure is very thin. At present, this structure is the largest hydrogen atom structure around galaxies discovered in our astronomical world. According to current theory, such a large-scale and low-density hydrogen atomic gas structure should not exist.
(Photo source: Official website of the National Observatory of Chinese Academy of Sciences)
Continuously absorbing hydrogen atomic gas:
Evolution process of galaxies in the universe
Duan Yulong: Can you briefly introduce the evolution process of galaxies in the universe?
Xu Cong: In fact, the evolution process of galaxies is a process of constantly absorbing hydrogen atomic gases from the universe and then turning them into stars.
From the history of star formation, stars are produced from very dense molecular gases. These molecular gases have to come from the thinner hydrogen atomic gas. Since the hydrogen atom gas cools down, or after collapses unstable, it will become very dense molecular gas nuclei, which will produce stars.
The celestial bodies, galaxies, stars, etc. in the universe we are discussing are the most basic things, and they are all directly related to hydrogen atomic gas. It can be said that hydrogen atomic gas is the basis and source of the formation of these celestial bodies.Stephen’s Five-layer Galaxy under the display of the medium-infrared instrument in
(Photo source: NASA, ESA, CSA, STScI)
Duan Yulong: Does that mean that we will study these hydrogen atomic gases, which is very helpful for us to better understand some basic laws such as the evolution of the universe and the details of the formation of celestial bodies?
Xu Cong: can be said like this. In fact, a very important link in modern cosmology, especially the theory of galaxy evolution, is the study of hydrogen atomic gases. But it is not particularly easy to study. Until now, the related equipment of the radio band is still being improved.
Expert information
1 Duan Yulong Chinese Science Popularization Writers Association Director and Beijing Science Popularization Ambassador
2 Xu Cong Researcher at the National Observatory of the Chinese Academy of Sciences
Content source: This article is co-produced by Beijing News Radio "Illuminating the Deep News" and Tencent News "Let's Talk to Scholar"
Editor: Chen Jiali (Internship)
Producer: Liu Yingying
3Supervisor: Liu Yingying
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