Remember the photo photo of the M4 black hole released 87 years ago, which resembles a "doughnut"? Now, through the efforts of scientists, the black hole has a panoramic photo, from a "doughnut" to a "chicken's paw".

Sixteen radio telescopes were connected to form a telescope with an aperture equivalent to the diameter of the Earth. This is the first time that humans have imaged the ring-shaped structure around the M16 black hole at a wavelength of 3.5 mm, and it can be said that a panoramic picture of the black hole has been taken, which at first glance looks like a "chicken's paw". The images show the link between accretion flow near the central supermassive black hole and the origin of jet currents, and the results were recently published in the international academic journal Nature.

The completion of this work is an international cooperation team led by Lu Rusen, a researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, with members from 17 countries and regions and 64 research units, with a total of 121 members. There are some post-80s and post-90s figures in the team, and the reporter interviewed this energetic young team to hear the stories behind their photos of black holes.

"This is the scenery you will see in interstellar travel"

On this latest panorama, there are black holes, accretion flows around black holes, and jets "tails" that extend from near the accretion disk into the distance. The M87 black hole took on a 3.5 mm image that surprised the researchers with a "doughnut" shape, nearly 1 percent larger than the old 3.50 mm photograph.

"Imagine that if we were on an interstellar journey towards our protagonist, the black hole of M87, this picture shows the scenery we saw on the journey." Lu Rusen, the first author of the paper, said.

The new image, taken April 2018-4, 14, is the subject of the M15 black hole, located at the center of the Messier 87 galaxy, the central giant elliptical galaxy of the Virgo cluster, about 87 million light-years from Earth, 5500.65 billion times the mass of the Sun. It has jets up to 5000,<> light-years long, which is "very photogenic."

"Previously we have seen black holes and jets separately in separate images, but now we have taken a panorama of black holes and jets in a new band." "The ring structure we saw before became larger and thicker at 3.5 millimeters. This suggests that in the new image, it can be seen that the matter falling into the black hole produces additional radiation. This allows us to get a fuller picture of the physical processes surrounding black holes. ”

According to him, the matter around the black hole is thought to fall into the black hole during the accretion process. No one had ever imaged it directly.

This time, the telescopes participating in the photographs included 14 radio telescopes of the Global MillimeterWave Very Long Baseline Interferometry Array (GMVA), the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile, and the Greenland Radio Telescope (GLT) in Greenland.

According to the research team, the ring-shaped structure measured by GMVA has a diameter of 64 microarcseconds, which is equivalent to the size of "astronauts on the moon who see a 13-centimeter ring fill light when they look back at Earth."

"The shorter the observation wavelength, the higher the weather requirements of the observation conditions. Observation time is quite limited every year, and applications for observation time are very competitive, and the team has to represent the most cutting-edge level in this field. Jiang Wu, associate researcher at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, told a reporter from China Youth Daily.

Jiang Wu's job is to process the observed data. According to him, global coordinated observation is required when taking pictures, so it is required that the observation weather observation conditions of all stations are suitable, and the most suitable time is usually April, "both northern and southern hemispheres are suitable."

He told reporters that after winning the "Big Mac" class telescope ALMA to join the observation array, the entire team had "high expectations" for the shooting results.

After processing the data, "unprecedented new features" were revealed, which excited the members of the research team. Before that, many people thought that "doughnuts" would not be seen at this wavelength. Lu Rusen admitted that even he did not think of it.

"By adding ALMA and GLT to the GMVA observations, which greatly improved the imaging capabilities, we gained a new perspective. We did see the tridentate jets that we learned about in earlier VLBI observations. Thomas Krichbaum, of the Max Planck Institute for Radio Astronomy in Bonn, Germany, said, "Now we can see how jets emerge from rings around the central supermassive black hole, and we can now also measure the diameter of rings around black holes in another wavelength." ”

"To explain the 'doughnut' in physics"

Radio radiation from the black hole M87 is produced by the interaction of high-energy electrons and magnetic fields, a phenomenon known as synchrotron radiation. At a wavelength of 3.5 millimeters, the new observations reveal more details about the position and energy of these electrons. They also tell researchers something about the nature of the black hole itself: it's not "hungry," consumes matter at a low rate, and converts only a fraction of it into radiation.

In addition, in the inner region close to the black hole, the width of the radiation is wider than expected. This could mean that not only is gas falling around the black hole, but it may also be "a wind blowing out, causing turbulence and chaos around the black hole."

To understand the source of this larger, thicker "bright ring," the researchers had to test different situations using computer simulations and finally concluded that "the larger extent of the bright ring is related to accretion flow."

In the process of processing "raw data" into "cooked data", the research team did 4 correlation analyses before and after, "overcoming the torment of back and forth rework", and finally obtained the most reliable "cooked data".

Reconstructing observational images from "familiar data" also encountered "unprecedented challenges". The new photo is an image with a large field of view, containing many components that vary greatly in brightness. The team brought together the experience of many collaborators around the world, and after various trials and tried-and-it-and-tested trials, finally overcame these difficulties.

The Greenland telescope in the array is a new radio telescope that was still in the commissioning phase when participating in observations. During observations, the telescope's phase rotator was misconfigured. The team discovered this problem only after the fact and had to develop special algorithms to solve the problem when processing the data.

Yang Hai, the youngest member of the team at the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, is to "figure out how to interpret" the observed data in the way of physics. He is a post-90s generation who is a member of the Black Hole Accretion and High-Energy Astrophysics Research Group and a student of researcher Yuan Feng.

"We get data on the velocity, density, and strength of the black hole's jet, and then use a computer to simulate what it looks like. Finally, think about how to build its theoretical model and find out its theoretical explanation. Yang Hai told a reporter from China Youth Daily and China Youth Network.

In 2014, when the movie "Interstellar" was released, he had always been interested in science fiction sitting in the cinema and was deeply shocked by the black hole simulated on the big screen. At the time, he did not expect that in a few years, his work would be closely related to black holes. But his interest in astronomy and black holes is as good as it is for him.

As a "novice novice" in the field, Yang Hai followed the teachers to take pictures of black holes, in this process, he was inevitably nervous, basically did not use the memes commonly used by young people in the team's group, and tried not to speak the popular Internet language.

However, when discussing offline, the post-90s generation is not so nervous. He would boldly pitch his ideas and then listen carefully to the teachers, "telling me if it was good to do this and if it was worth the time to try."

From home to work, Yang Hai maintained a two-point life, and also maintained the patience of sitting on the "cold bench" of basic research. Occasionally, he will also notice that some classmates have joined technical companies after graduation and received salaries several times higher than him. His heart doesn't have too many waves in his heart, and he thinks it's more important for him to produce results in research.

"In the future, we will also 'make a movie' for black holes"

In Lu Rusen's words, the follow-up work also includes "filming" and even "making movies" for the M87 black hole.

Humans have set their sights on M87, dating back to 1781. At that time, the French astronomer Charles Messier published the famous Messier catalog, which contains 103 nebula-like objects. Messier named these objects after the letter M and the number, M87 being one of them, which means "the 87th object in the Messier catalogue".

However, it wasn't until more than 100 years later that humans realized that M87 was not a nebula, but a galaxy. Astronomers saw "a strange beam of straight rays emanating from the center of a hazy spot," the first time in human history that jets in celestial bodies were observed. The Event Horizon Telescope (EHT) successfully photographed the supermassive black hole at the center of galaxy M2017 in 87, another century later.

Human beings are curious about the process of looking up at the stars, and they have experienced hardships, but they have never stopped. The exploration of the M87 is not over.

"The 3.5 mm wavelength image displayed this time can be said to represent the latest achievement. But in order to unravel the mystery of the physical mechanisms of the formation, acceleration, and collimation propagation of the central supermassive black hole of M87 and its relativistic jets, we need to take more high-quality images of colors, including photos of black holes with submillimeter wavelengths of 0.8 mm or less, and panoramic images of black holes and jets as long as 7.0 mm wavelengths. Researcher Shen Zhiqiang, director of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, said.

Further observations and a more powerful array of radio telescopes will continue to unravel its mysteries. In the future, millimeter-wave observations will study the temporal evolution of the M87 black hole and obtain a multicolor view of the region of the black hole at the center of M87 by combining different colored "radiolight" images.

"The millimeter wave technology we used this time can be used in communications and other fields; Telescope construction also involves cutting-edge technologies in terms of structure and mechanical design, which can also be transformed in the future. From this point of view, much of the work we are doing now is helpful in promoting the application of science. Jiang Wu told a reporter from China Youth Daily and China Youth Network.

Jiang Wu is a post-10s generation who has been engaged in scientific research for more than 80 years, in his view, basic research and real life often seem to have little to do with it, in fact, only the continuous advancement of basic research can drive the most cutting-edge and advanced technological development, and improve human life and production methods.

Jiang Wu also participated in the "shooting" of the first black hole photo, and now has obtained a new photo of the overall image of the jet. He felt that these years of experience were "very special" for him.

"I like to get into the essence of things, and I want to do basic research." He lamented to reporters, "If the work I do can make a certain contribution to this field and achieve certain scientific results, this is the most satisfying thing for me." ”

Zhongqing Daily / Zhongqing Net reporter Zhang Mi Source: China Youth Daily