At that time, the press conference of Peng Mei News (www.thepaper.cn) will bring express delivery to the press conference of Shanghai Observatory. Readers can quickly preview the background information related to this black hole study while moving small benches and sitting down to eat melon.
The film interstellar traverses the black hole in which the bright ring is surrounded by an accretion disk of gas.
Q: What is a black hole?
Answer: According to the calculation of Einsteins gravitational field equation, if a large amount of matter concentrates on a point in space, a distorted horizon of space-time will be formed around the singular point. Once entering this interface, even photons can not escape.
The prediction was made in 1916, but it was not until 1967 that Princeton University nuclear physicist John Wheeler first used the term black hole in a lecture and spread quickly.
Q: Since you cant see, how do you take pictures of black holes?
A: Although scientists cant see the body of a black hole, it can be traced back to the horizon where photons disappear, which is the limit we can see.
There are some luminescent phenomena around the black hole, such as when the black hole eats up the surrounding stars, it will tear the gas of the stars to its side, forming a rotating accretion disk. Black holes sometimes belch, and part of the accretion gas is ejected along the direction of rotation to form a jet.
Both accretion disks and jets produce bright light as a result of gas friction, as well as radiation at other frequencies.
Q: How to find a black hole?
A: Scientists can feel the existence of a black hole indirectly through its influence on the surrounding celestial bodies, especially the space-time distortion caused by its huge gravity, just as the mass of the earth can be inferred indirectly through the orbit and velocity of the moon.
Secondly, as mentioned above, accretion disks and jets emit light, accompanied by radiation at other frequencies.
Finally, the interaction of a black hole with another celestial body or another black hole produces a large number of gravitational waves, which are also detectable clues.
Q: Are there any confirmed black holes?
Answer: Yes. The first gravitational wave signal detected by humans is generated by the combination of two black holes.
The first powerful black hole candidate discovered by humans was Cygnus X-1, discovered in 1964, about 6,000 light-years from Earth. Cygnus X-1 has a partner it is eating, but the quality of the companion star is bigger than itself, which has caused widespread controversy. Hawking has bet (and lost) on its long-standing status. Scientists later measured that Cygnus X-1 had a mass of about 14.8 suns and a horizon radius of 300 kilometers. It should be a very small appetite black hole.
At present, scientists pay more attention to a kind of black hole candidate system, which is a soft X-ray transient source. Such systems consist of a small mass of dancing partners, usually quiet, but intermittent X-ray bursts occur, with intervals ranging from months to decades. Intermittent bursts are a good time to detect black holes.
According to theoretical calculations, there should be tens of millions of black holes in the Milky Way galaxy, and only 20 black holes have been confirmed.
Question: Which black hole was photographed this time?
A: Two supermassive black holes. One is the black hole SgrA*, the center of the Milky Way Galaxy, and the other is the M87 Galaxy in Virgo. The reason for choosing these two targets instead of the nearer star black holes in the Milky Way is that their horizons are large enough from the Earths perspective.
For a long time, scientists have discovered hundreds of billions of stars revolving around the center of the Milky Way Galaxy, speculating that there is a supermassive object there. According to calculations, the mass of SgrA* is about 4 million suns and the horizon radius is about 24 million kilometers. It sounds big enough, but given that the black hole in the galaxys center is far beyond 25,000 light-years (about 2.4 billion kilometers), the actual effect is equivalent to observing an orange on the moon on Earth or a golf pit in Shanghai in Beijing.
The supermassive black hole at the center of M87 is 6.6 billion times the mass of the sun and has a horizon about three times the orbit of Pluto. Of course, because of the distance, the actual effect of M87 central black hole on the Earth may not be much different from SgrA*.
Question: How can I take photos with such high resolution?
A: Global telescopes form arrays and observe jointly to form a large telescope with an effective aperture equal to the diameter of the earth. The virtual telescope, called the Event Horizon Telescope (EHT), consists of eight telescopes. They are: the Southern Pole Telescope; the Atacama Large Millimeter Array (ALMA) in Chile; the Atacama Pathfinder Experiment in Chile; the Large Millimeter Telescope in Mexico; and the Submillimeter Telesco in Arizona, USA. PE; James Clerk Maxwell Telescope (JCMT) in Hawaii; Submillimeter Array in Hawaii; and 30-meter millimeter-wave telescope at the Millimeter Radio Astronomy Institute in Spain. They jointly observed two black hole targets in April 2017.
Since 2018, the Greenland Telescope, the IRAMNOEMA Observatory in France and the Kitt Peak National Observatory in the United States have joined in the follow-up research and calibration work.
More than 60 research institutes around the world participated in the research, including Shanghai Observatory and Yunnan Observatory, affiliated to the Chinese Academy of Sciences, as well as Huazhong University of Science and Technology, Nanjing University, Sun Yat-sen University, Peking University, University of Chinese Academy of Sciences and Taiwan University. This is also the reason why Shanghai and Taipei jointly hold press conferences.
Q: Why are the photos taken in 2017 only published now?
Answer: Black hole photographs are difficult to take and wash out. Virtual large telescope arrays do not directly capture black hole images, but give a lot of data, which must undergo complex computer processing. There are also missing or blurred parts that need to be puzzled by scientists.
In addition, after the joint observation in April 2017, the research team also carried out some data collection and calibration work.
Source of this article: Peng Mei News Responsible Editor: Yao Liwei_NT6056