"After FAST moved to the commissioning phase, I began to succeed Mr. Nan Rendong as the Chief Engineer of China Sky Eye. The new design concept of FAST meant that we could not have any successful experience to draw on, and we had to establish a measurement and control method system adapted to the special working method of FAST. On March 7, 2023, at the second delegate channel of the first session of the 14th National People's Congress, Jiang Peng, chief engineer of China Tianyan FAST and researcher of the National Astronomical Observatory of the Chinese Academy of Sciences, told his story with FAST.
(Source: Video screenshot)
He said: "This telescope meets almost all my expectations for a legendary project, a huge engineering volume, ultra-high accuracy requirements, and extremely special working methods, which constitute a huge technical challenge in the industrial field. ”
So far, more than 800 new pulsars have been discovered with FAST's help, more than 3 times the total number of pulsars discovered by all other telescopes in the world during the same period.
Not long ago, still with the help of FAST, Jiang Peng and collaborators from Guizhou University, the University of Nevada and other units in the United States discovered a new star - a pulsar in a binary star system.
The pulsar and its companion are very close together and have a very short orbital period of only 53 minutes, which is unprecedented in previously discovered pulsar binary systems.
In such a close pulsar binary system, most systems have accretion , that is, the material on the surface of the companion star will be affected by the pulsar and leave the companion star, enter interstellar space, or be attracted by the pulsar and fall towards the pulsar. As a result, the companion star will have less and less material.
This process is very similar to the behavior of female spiders swallowing male spiders after mating, so astronomers have given this type of pulsar a name - spider pulsar.
There are two stages in the evolution of spider pulsars: in the first stage, the pulsar will get closer to the companion star, and the orbital period will gradually shorten; In the second phase, they move away from each other, and correspondingly, the orbital period gradually lengthens.
In this study, the team found that the pulsars and companion stars in this system are extremely close to each other, which is the closest period, that is, in the middle of the above two stages. Pulsar binary systems in this state have never been detected before.
Therefore , this is a direct detection of the shortest orbital period pulsed binary system. At the same time, both reviewers pointed out that this system is important for deciphering the evolution of near-spider pulsars, an extremely special and very interesting pulsar binary system.
In addition, this discovery also has a very broad application prospect. As the two reviewers pointed out, the discovery of this binary star system confirms an important part of the evolution of spider pulsar binaries, which connects the evolutionary trajectories of other spider pulsars that can be observed so far, so it can connect the evolution theory of spider pulsars.
If this system can be studied in depth, more information can be obtained about the evolution of binary stars, which is of great significance for exploring the evolution of pulsar binary star systems, the formation pathway of close X-ray binary stars, and the interaction between millisecond pulsars and companion stars.
A few days ago, a related paper was published in Nature as "A Binary Pulsar in a 53-minute Orbit" [1].
Figure | Related papers (Source: Nature)
Associate Researcher Pan Zhichen of the National Astronomical Observatory, Lu Jiguang and Chen Hailiang of the Yunnan Astronomical Observatory are co-authors, and Jiang Peng and Han Jinlin, Researcher of the National Astronomical Observatory, and Professor Zhang Bing of the University of Nevada are co-corresponding authors.
(Source: Nature)
What is the point of discovering new pulsars? This has to start in 1967, when British astronomer Jocelyn Bell Burnell discovered a new celestial body, a pulsar, which won the 1974 Nobel Prize in Physics, and she was also known as the "mother of pulsars".
Such objects can emit very accurate periodic radio pulses, like signals from some kind of intelligent life, and early people speculated whether this could be emitted by other civilizations in the universe.
However, more and more pulsar radiation signatures were observed, and scientists confirmed that it was a special object and associated it with the neutron star predicted by the former Soviet physicist Lev Davidovich Landau in the 2030s.
Through further observations and analysis, astronomers believe that it is slightly more massive than the sun, but has a radius of only about 10 kilometers and a strong magnetic field.
It is generally believed that the radio radiation of pulsars comes from its own high-speed rotation and its own magnetic field and material interaction. When the magnetic field rotates, a strong electric field is induced by the principle of electromagnetic induction, and the strong electric field can accelerate the particles to produce radiation.
Such objects also have strong electromagnetic and gravitational fields. Therefore, relying on human laboratories on Earth, it is difficult to create such magnetic fields. Its density exceeds the density of nuclear matter, and it is even more difficult to achieve in laboratories on Earth. These extreme conditions make pulsars natural strong-field laboratories.
By studying pulsars, it is possible to conduct in-depth research on strong field physics, thereby advancing the development of basic science. In 1974, American physicists Russell Hulse and Joseph Hooton Taylor discovered a radio pulsar, PSR B1913+16, and proved that it formed a binary star system with another neutron star.
The Royal Swedish Academy of Sciences called the discovery "a new opportunity for the study of gravity" and that the binary star system was successfully used to test one of Einstein's boldest predictions: gravitational waves emitted by objects accelerating at an accelerated motion. With this, the two shared the 1993 Nobel Prize in Physics.
So, how did the star come about? Jiang Peng said: "In fact, this system was discovered in two pulsar search projects. One is the silver sky survey project led by Mr. Han Jinlin, and the other is the globular team pulsar search project led by our team Pan Zhichen. ”
At that time, the former found the signal of the pulsar and determined that it was a pulsar binary system, but the orbit has not yet been determined. The latter, together with colleagues from the FAST team, independently discovered this signal in FAST historical observations and determined that its orbital period was 53 minutes.
This parameter is very rare, and the entire research team was very excited and immediately began to analyze the system. The analysis is divided into three areas:
On the one hand, they contacted the team of Academician Han Zhanwen of the Yunnan Astronomical Observatory to analyze the formation mechanism of this system from the perspective of pulsar binary star evolution theory, and determine its state in the evolution process. As the analysis results come out, they increasingly believe that such a short orbital period indicates the extraordinary formation of this binary star system, and there are more unknown mysteries waiting to be revealed;
On the other hand, they folded the pulsar's radiation with the help of the pulsar's parameters, thus obtaining a high-precision pulse shape. During this period, they collected all the data and invested all the observation time that could be used, which lasted more than two years;
Third, under the guidance of Professor Zhang Bing of Internalized University in the United States, the research group discussed in depth the evolution series of pulsar binary stars and the conditions for limiting the radius of companion stars through the Roche lobe, and added the corresponding scientific content, and the scientific significance of the article was greatly improved. He was prompted to look for the X-ray counterpart of the star and studied the possible scientific implications of the X-ray observational data.
Professor Xu Renxin of Peking University is one of the collaborators of the paper, and has been involved since the beginning of the research, providing assistance in binary star evolution, pulsar radiation mechanism and orbital state analysis, and meticulously assisting in the revision of the text. All collaborators in this paper are actively involved in the research work, contributing their knowledge, putting forward their own opinions, and enhancing the significance of the research.
In this study, the model deduction of binary star evolution is very memorable. Jiang Peng said: "At the beginning, we found that it is difficult for binary stars to evolve this parameter of 53-minute orbital period under the general model framework, which is obviously unreasonable, because our observations confirm the existence of such a system." ”
As the research progressed, they found that the evolution process of pulsar binary stars is extremely complex, involving the abundance of heavy elements in the binary system, the relationship between the binary system and its nearby globular cluster M71, the possible evolutionary age range of the binary star system, the possible type and mass of the companion star, the orbital plane and the observer's line of sight, and many other aspects.
These factors have an impact on the limiting orbital period of pulsar binary system evolution. Under the combination of various factors, the limit of pulsar binary orbit can be pressed very low, so there is a lot to discuss in the current binary evolution theory.
Therefore, Jiang Peng and his collaborators explored the details of the model layer by layer before finally reaching the conclusions in the paper. During this time, they limited the size of the companion star according to the Roche lobe, an idea that played a crucial role in model limiting.
"At the same time, this also fully reflects the complexity of scientific research, even if many basic theories are extremely clean and concise, the actual system is still extremely complex and unpredictable." Jiang Peng said with emotion.
In addition, the binary system discovered this time has an orbital period of only 53 minutes. In the search for pulsars , such short-period pulsar binary systems are extremely difficult to detect because they do not know the period of the orbit and other relevant parameters in advance.
Therefore, the search process requires a lot of computing resources, and taking full advantage of FAST sensitivity to try various possible pulsar signal search methods, which is time-consuming and has a very low output probability.
During the study, the team searched using short-term observations, and then stitched the results back to finally determine the binary parameters of the star.
"First, this reflects the serious and responsible research attitude and flexible scientific spirit of scientific researchers; Second, this also shows that the FAST telescope, as the world's most sensitive single-aperture radio telescope, its ultra-high sensitivity does have a strong propulsion effect on science. Jiang Peng said.
Figure | Jiang Peng (Source: Infographic)
In the future, the research group also hopes to continue to use FAST to monitor M71E, and the more continuous the observation, the more possibilities it brings. On the other hand, they are also collecting more multiband observations as evidence to further limit the model.
Resources:
1.Pan, Z., Lu, J.G., Jiang, P. et al. A Binary Pulsar in a 53-minute Orbit. Nature (2023). https://doi.org/10.1038/s41586-023-06308-w