China News Service, March 25. According to the website of the Shanghai Observatory of the Chinese Academy of Sciences, an international team led by Yuan Feng, a researcher at the Shanghai Observatory of the Chinese Academy of Sciences, recently used the jet of the supermassive black hole in the center of the M87 galaxy as the research object. The correctness of the black hole jet model is studied.
The research team calculated the radiation predicted by the two models and compared it with the observations. They found that the jet predicted by the model that extracts the rotational energy of the black hole through the magnetic field is very consistent with the actual observation results, while the jet predicted by the model that extracts the rotational energy of the black hole accretion disk through the magnetic field is very consistent. Models have difficulty explaining observations. The research team further analyzed the physical mechanism of "magnetic reconnection" in the black hole jet and found that this is due to the magnetic field in the M87 black hole accretion disk producing a "magnetic burst". This burst can produce strong disturbances to the magnetic field, which can propagates over long distances, causing magnetic reconnection in the jet. The relevant research results, titled "Modeling the inner part of the jet in M87: confronting jet morphology with theory", were published in Science Advances on March 23, 2024, Beijing time.
A black hole is a very strange celestial body in the universe. It has such a strong gravitational force that even light cannot escape its gravitational pull within the radius of the black hole. However, more than 100 years ago, astronomers discovered through observations that just outside the radius of the black hole, the black hole can eject a powerful outflow containing matter and energy - a jet - at a speed close to the speed of light. Images taken by the telescope show that the jets are ejected straight out to great distances like a beam of laser, and the length of some jets can even far exceed the scale of the galaxy.
How are mysterious jets formed? This problem has been studied for more than 100 years, and many scholars, including Penrose, the Nobel Prize winner in physics, have studied it. Currently, there are two main models in this research field. One is to extract the rotational energy of the black hole through a large-scale magnetic field, that is, the "extracting the black hole rotational energy" model; the second model also requires a large-scale magnetic field, but it is different from the first model. , the magnetic field extracts the rotational energy of the accretion disk, that is, the "extracting the rotational energy of the accretion disk" model.
No matter which model it is, astronomers are trying to solve the problem of the energy source of the jet. However, can the jets produced by these two models be consistent with observations of the jet's morphology, width, velocity field, polarization, etc.? Another important question is, which of the above two models of jet formation mechanism is correct? An international collaborative team led by researcher Yuan Feng from the Shanghai Observatory of the Chinese Academy of Sciences conducted research on these two issues. They found that a model that extracted the black hole's rotational energy through magnetic fields predicted jets that were very consistent with observations, while another model struggled to explain the observations.
The team conducted specific research using the jet of the supermassive black hole at the center of the M87 galaxy as an example. The supermassive black hole at the center of the M87 galaxy is the "star black hole" that captured mankind's first black hole photo by the Event Horizon Telescope (EHT). First, the research team used large-scale numerical simulation methods to solve the general relativity magnetohydrodynamics equations and obtained the black hole accretion flow and the jets generated by the above two mechanisms. To calculate the radiation from the jet and then compare it with observations, it is key to obtain the energy spectrum and spatial distribution of the radiating electrons. The research team hypothesized that electron acceleration occurs through a "magnetic reconnection" mechanism in the jet. Under this assumption, they considered the physical mechanism of accelerated electrons by magnetic reconnection, combined with the results of particle acceleration research using kinetic theory, and obtained a steady-state electron energy distribution equation by solving the equations of different spaces in the jet. Energy spectrum and number density of electrons. With this information, coupled with the magnetic field strength, gas plasma temperature, velocity and other results obtained from the black hole accretion numerical simulation, the radiation transfer in the jet can be calculated under the framework of general relativity and various predicted observation results can be obtained. to compare with real observations. The research results show that the jet shape predicted by the "extracting black hole rotational energy" model is in good agreement with the actually observed jet shape. More detailed analysis shows that other results predicted by the model, such as the "edge brightening" of the jet, jet width, length, velocity field, etc., are also in good agreement with observations. The predictions of the "extraction of accretion disk rotational energy" model are inconsistent with observations.
In addition, the research team further analyzed the physical mechanism of magnetic reconnection and found that this is due to the magnetic field in the M87 black hole accretion disk producing a "magnetic burst". This burst can produce strong disturbances in the magnetic field, and the disturbance can propagate long distances, leading to magnetic reconnection in the jet.
Researcher Yuan Feng said: “This work builds a bridge between the dynamic model of jet formation and the various properties of jets observed by telescopes. It proves for the first time that this famous dynamic model can not only solve the problem of jet The energy problem can also explain the observation results of various other jets. This provides a breakthrough for our next step in understanding more unsolved mysteries near black holes."
The picture shows the comparison between the jet shape predicted by the "Extracting Black Hole Rotational Energy" model and the actual observed jet shape. It can be seen from the figure that the theoretical predictions agree very well with the observations. More detailed analysis shows that other results predicted by the model, such as the "edge brightening" of the jet, jet width, length, velocity field, etc., are also in good agreement with observations. The predictions of the "extraction of accretion disk rotational energy" model are inconsistent with observations. Image source: Shanghai Observatory website of Chinese Academy of Sciences