Whether the cosmic string sits there is, the answer may be hidden in a 21 cm hydrogen line.

Microwave background radiation is the oldest light in the universe, since the Big Bang, after a long time and space to become a microwave, filled throughout the space, covering up countless unknown secrets, the cosmic string is one of them. Recently, Oscar Hernandez, a researcher at McGill University in Canada, and others shared an idea on arXiv.org, an online database of preprints of the global scientific literature, that they could use convolutional neural network programs to find traces of a particular cosmic string in the “noise” of the cosmic microwave background radiation.

But the method is still difficult to practice, because it is almost impossible to obtain sufficiently clear cosmic microwave background data for the program to “track” the cosmic strings. So the researchers are pinning their hopes on a new method of detection, “the perturbation intensity measurement of the 21 cm hydrogen line.”

What exactly is a cosmic string? Why are so many astronomers and physicists so enthralled? How does the “disturbing intensity measurement of the 21 cm hydrogen line” provide new ideas for people to find cosmic strings?

Whether the cosmic string sits there is, the answer may be hidden in a 21 cm hydrogen line.

Origin: The Energy Relic of Phase Change

The Big Bang theory is the theory of cosmic formation, which is recognized by most scholars in the academic circles, and it is also one of the most influential theories in modern cosmology. However, the theory is not perfect.

The Big Bang theory holds that the universe has a history of evolution from heat to cold. During this period, the universe continued to expand, allowing the density of matter to evolve from dense to sparse, i.e. the universe was formed by a dense, hot wonder that expanded after a big bang.

In theory, this evolution should be uniform and homogenous on a large scale. But in fact, the high density of celestial bodies gathers into galaxies, clouds and so on pervades the near-vacuum interstellar.

Practice is the only criterion for testing truth. This uneven cosmic fact clearly requires a new explanation. What caused the formation of giant groups such as stars and galaxies that destroyed the uniformity of the universe? Some scholars have put forward the concept of “cosmic string”. They believe that the universe may be filled with a large number of cosmic strings, with its powerful gravity to attract the surrounding matter, become the star, the birth of the “seed” of the galaxy. It is only by the existing means of detection that no trace of the cosmic string has been found.

So, what exactly is the cosmic string?

“Before I answer this question, I would like to mention a relatively familiar noun: phase change. Cai Yifu, a professor in the Department of Astronomy at the School of Physics at the University of Science and Technology of China, told Science and Technology Daily.

Phase changes abound in our daily lives, such as freezing water into ice, ferromagnets turning into paramagnets, etc. The history our universe goes through is a history of constant phase-changing thermal expansion, in which elementary particles are produced, elements are synthesized into elements, and elements end up combining the familiar physical structures we see. “Phase change processes are accompanied by energy release, and one way of energy release is to form particle structures at all levels mentioned earlier. “Cosmic strings are the same energy structure symbiosis that release energy as the universe goes through phase changes. “

Of course, the result of energy release also has other forms, such as cosmic walls or magnetic monopoles. But theoretically, such a pattern is far less stable than elementary particles and cosmic strings, and will disappear later in the evolution of the universe. The cosmic strings are unusually stable and strong, making it possible to survive and remain in the universe to this day. Therefore, even if the existence of cosmic strings has not yet obtained the “real hammer”, but still attracted many scholars at home and abroad.

Features: String fine large light distortion

Although the cosmic strings have not been observed in the true sense, we can theoretically infer many of the characteristics of cosmic strings.

Li Xinzhou, then director of the Institute of Theoretical Physics at East China University of Technology, published a paper in the 1990s that the cosmic string smaller, its horizontal scale is only 10-29 cm, but the mass is great, its line density is about 1022 grams per centimeter, or 107 solar mass per light year.

So the gravitational pull of the cosmic strings is impressive. General relativity points out that gravity is equivalent to space-time bending. As a result, the space around the cosmic string softens a conical distortion, orbiting a cosmic string around a loop less than 360 degrees. Such distortion turns the cosmic string into a lens, allowing the photons emitted by the celestial body behind the cosmic string to reach the observer through two possible paths, so that the celestial body is refracted into two images of equal brightness.

What does that mean?

In recent years, researchers have discovered pairs of galaxies or quasars that are almost equally red.” Some scholars have asked: Will these not be real physical phenomena, but the same light source due to the gravitational lensing effect of cosmic strings formed by the dual image? Although it is not known whether the conclusion is correct or not, it has to be acknowledged that the existence of cosmic strings provides us with new ideas for observing many magical astronomical phenomena.

Studying cosmic strings means more than that. In Tsai’s view, all cosmic strings can release gravitational waves, and although the total is small, physicists hope to make a breakthrough in the now-booming gravitational wave astronomy. Moreover, if the cosmic string happens to be live at the birth time, then such cosmic strings are superconducting strings, there will be a lot of discharge phenomena, just as we see high-voltage wires when the wire is exposed discharge phenomenon similar, or may be able to explain the origin of various interesting astrophysical effects, such as rapid radio storms.

In addition, because cosmic strings are produced very early and may be possible in the same era or earlier, cosmic microwave background radiation is affected by cosmic strings.

Cai Yifu told Science and Technology Daily that the cone deformities of space around the cosmic strings are difficult to detect in a static state, but if the cosmic microwave background radiation and cosmic strings in relative motion, then this lack of angle will lead to temperature differences in cosmic microwave background radiation. This is why many scholars devote themselves to the search for cosmic strings in the cosmic microwave background radiation.

Detection: 21 cm hydrogen line or main force

However, some scholars do not appreciate the over-reliance on cosmic microwave background radiation to detect cosmic strings.

Oscar Hernandez in the article, said that the current human-made microwave instruments are not perfect, the resolution is limited, these factors, will cause a certain degree of information loss, any reliance on the cosmic microwave background radiation research, can not hide these errors. Therefore, we need a way to measure radiation beyond the cosmic microwave background, and perhaps the “21 cm hydrogen line disturbance intensity measurement” will provide us with a richer map.

According to Cai Yifu, the disturbance intensity measurement of the 21 cm hydrogen line is a future astronomical observation method, and the technology is still in development.

After the Big Bang, protons and electrons in the universe combined to form atoms. Hydrogen accounted for the vast majority of ordinary matter at the time, but it would not release or absorb photons in the electromagnetic spectrum, so hydrogen was almost invisible and the universe was transparent. But the only electron in the hydrogen is a “freak”, the electron originally has a smooth, counterclockwise two spin direction, when its real spin in these two directions change back and forth, it will release or absorb a photon, the wavelength of the photon is about 21 cm, so its radiation line is called 21 cm hydrogen line.

As early as the 1940s, scientists theoretically predicted the existence of the astronomical observation symofing 21 cm hydrogen line, which was quickly confirmed by observations, Cai said. But because these signals are so weak that we can only confirm the existence of these signals but cannot accurately measure size and other properties, astronomical experiments are still working to improve measurement techniques.

The expansion of the universe causes a redshift, and the wavelength of the 21 cm hydrogen line we observe today will also increase. There is density disturbance in the universe, i.e. some regions expand faster, some regions expand more slowly, and the measured wavelengthof of the 21 cm hydrogen line will vary slightly. This can be counter-edited to the then 21 cm hydrogen line experienced how the journey finally reached Earth.

“If accurate observations are possible, the 21 cm hydrogen lines that occurred in the early universe will record the state of the universe at that time, including the effects of the cosmic strings.” Tsai said.

Of course, this measurement is not just to test the existence of cosmic strings, it can also help people better understand the state of the universe during the period of heavy ionization and the earliest star formation period, and is therefore a key area for future astronomical experimental techniques to make breakthroughs. (Intern reporter Yu Ziyue)