The first photograph of a black hole in history was developed for about two years, and participants were also present in China.

 The first photograph of a black hole in history was developed for about two years, and participants were also present in China.

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Black Hole Photo Start! 60 seconds to look at the 200-year history of human black hole pursuit (source: original)

At 21:00 pm on April 10, a press conference was held in six parts of the world (Brussels, Chile, Santiago, Shanghai, Taipei, Tokyo, Japan and Washington, USA) to announce the first successful capture of the worlds first black hole image using a virtual radio telescope the size of the Earth at the center of a nearby supergiant elliptical galaxy, M87.

The significance of this image is extraordinary. It provides direct visual evidence for the existence of black holes, which makes it possible to verify Einsteins general relativity in a strong gravitational field and to study carefully the matter accretion and relativistic jet near black holes.

According to reports, the released black hole image reveals a black hole in the center of the supermassive Galaxy M87 in the Virgo Cluster, 55 million light-years away from Earth and 6.5 billion times the mass of the sun. Many features of the image are in good agreement with the predictions of Einsteins general relativity theory, which is further validated in the extreme environment of strong gravity. By studying this image, humans will reveal more about the nature of celestial bodies such as black holes.

1. What exactly does a black hole look like behind the veil of mystery?

The protagonist of the conference is a supermassive black hole in the center of Virgos supergiant elliptical galaxy M87, which is 6.5 billion times the mass of the sun and about 55 million light-years away from Earth.

Photographs of black holes released in six locations around the world.

The published photos show a bright ring structure with a black center, which looks a little like an orange doughnut. The black part is the shadow cast by the black hole, and the bright part is the accretion disk rotating around the black hole at high speed.

In this image, the supermassive black hole (M87*) at the center of M87 galaxy is shown. The top image is April 11, 2017, and the bottom three images are M87* on April 5, 6 and 10, 2017. The weak region in the center of the image is called black hole shadow. The ring-shaped asymmetric structure around the image is caused by the strong gravitational lens effect and the relativistic beam effect. The spin direction of the black hole can be determined by the asymmetry of the upper (north) and lower (south).

2. How meaningful is it to photograph a black hole successfully?

First, taking pictures of black holes enables us to understand more detailed features of black holes, and helps astronomers understand the formation mechanism of jet and accretion disk structures, Zhang Hongbao, associate professor of physics at Beijing Normal University, introduced.

Secondly, the black hole is a massive black hole located in the center of the galaxy, which is considered to be closely related to the evolution of the whole galaxy. The observed black hole images are expected to reveal the relationship and mechanism between the two.

In addition, the general relativity effect near black holes is very obvious. More than a hundred years ago, Einstein proposed the general relativity theory, which combines time and space into a four-dimensional space-time, and proposed that gravity can be regarded as a distortion of space-time. One of the important predictions of this theory is that when the mass of an object collapses, it can be concealed in the event horizon, within the sphere of influence of the black hole, where gravity is so strong that even light cannot escape.

Taking pictures of black holes gives us an opportunity to test whether the real situation near black holes conforms to the theoretical predictions of general relativity and to test general relativity again.

3. What kind of black hole is suitable for photography?

In fact, black holes do not exist in isolation. The center of a black hole is a singularity. There is a lot of gas around it. According to Professor Gou Lijun, a black hole researcher and researcher at the National Observatory, because of the strong gravity of the black hole, gas will fall towards the black hole. When these gases are heated to billions of degrees, they emit intense radiation. At the same time, black holes also eject material and energy outward in the form of jet and wind.

However, although the shadow of a black hole can be seen, not all black holes meet imaging requirements. Because the size of event horizon is proportional to its mass, it also means that the larger the mass of black hole, the larger the event horizon, and the more suitable for imaging. Therefore, supermassive black holes close to us are perfect candidates for black hole imaging.

Two of the best known candidates for photographing with this virtual telescope are SgrA*, the central black hole of the galaxys central galaxy, and M87*, the central black hole of the nearby radio galaxy M87.

SgrA* has never been seen directly before, 26,000 light-years away from Earth, but its nearby stars are affected by it, so scientists believe that it really exists.

In addition, because Sagittarius SgrA* is surrounded by cosmic dust and gas, the difficulty of observation is greatly increased. Astronomers have assembled eight telescopes in six locations in Antarctica, the Americas and Europe to form the Event Horizon Telescope, which together emits narrow-band radio waves that can penetrate dense nebulae around black holes to focus the famous dark place.

In order to increase detection sensitivity, EHT records a large amount of data. In April 2017, the data rate of each station reached an astonishing 32Gbit/s. During the five-day observation period, eight stations recorded about 3500 TB data (equivalent to 3.5 million movies, at least several hundred years to see!).

EHT uses dedicated hard disks to record data and send them back to the data center for processing. There, researchers use supercomputers to correct the time difference between electromagnetic waves arriving at different telescopes, and integrate all the data to achieve signal coherence.

On this basis, after nearly two years of post-processing and analysis of these data, human finally captured the first black hole image.

4. What is the Event Horizon Telescope (EHT) project? China also has participants

In April 2017, the Event Horizon Telescope started taking pictures of black holes and took about two years to flush them. Some domestic institutions, including the Shanghai Observatory of the Chinese Academy of Sciences, participated in the international cooperation.

In addition, Chinese scientists have long paid attention to high-resolution black hole imaging research. Before the formation of EHT international cooperation, many related works with international display have been carried out. In this EHT cooperation, Chinese scientists jointly promoted EHT cooperation in the early stage and participated in the application of EHT telescope observation time. At the same time, they assisted JCMT telescope in observing and participating in data processing and theoretical analysis of results, which made a positive contribution to EHT black hole imaging.

The Event Horizon Telescope project consists of 13 cooperative organizations, one of which is the Center for Astronomical Sciences of the Chinese Academy of Sciences (CAMS). CAMS was established by the National Observatory of the Chinese Academy of Sciences, the Zijinshan Observatory and the Shanghai Observatory. The Shanghai Observatory took the lead in organizing and coordinating domestic scholars to participate in the cooperation.

Yuan Feng, a researcher, deputy director of the Shanghai Observatory and director of the Academic Committee of the Chinese Academy of Sciences, once introduced that direct observation of black holes is equivalent to taking pictures of curved space-time, requiring telescopes with high resolution. If the millimeter-wave telescope is used for observation, the caliber of the telescope needs to reach the same length as the diameter of the earth according to the formula. If an optical telescope needs to be several kilometers in diameter, an infrared telescope needs to be 10-100 kilometers in diameter. At present, the largest telescope built by human beings is a radio telescope with a diameter of only 500 meters, which is located in Guizhou, China.

To reach long-distance black holes and penetrate diffuse gases and high-temperature gases, a giant telescope equivalent to the size of the Earth is needed. It is the EHT that accomplishes this task.

The Event Horizon Telescope is not a traditional observation platform, but an array of antennas located in the United States, Mexico, Chile, France, Greenland and Antarctica. According to astrophysicist Jason Dexter of the University of California, Berkeley, This observation program is an unprecedented experiment, and we will get a clearer picture of the black hole around it. Image signal.

If the technology matures, he said, surprising observations could be made in the next few years. Observing Sagittarius A*from the Earth is like observing a grapefruit on the moon, but the Event Vision Telescope is competent for this task. Its resolution can observe an object on the moon that is close to a golf ball in size.

Source: Gu Ying_NN6577, responsible editor of Beijing News