After seeing the photograph of the black hole, some people on social media networks jokingly said it looks like a "doughnut".
Yet it is a "doughnut" prepared by overcoming extreme challenges. Creating the EHT was a formidable challenge in itself, as it required upgrading and connecting a global network of existing radio telescopes deployed at a variety of high-altitude sites, from volcanoes in Hawai'i and Mexico and mountains in Arizona and the Spanish Sierra Nevada to the Chilean Atacama Desert and Antarctica.
This is to say the EHT linked up multiple radio telescopes around the world, forming a virtual scope the size of the Earth with unprecedented sensitivity and resolution. And these radio telescopes worked together for several years to help the researchers piece together the first photo of the black hole.
Of course, photographing the interiors of a black hole is impossible, because any light that strays close to one of these gravitational monsters is lost forever. This point of no return is known as the "event horizon", hence the name Event Horizon Telescope.
What the team of researchers did, in fact, was to collect data from space through wavelengths. The researchers then picked the useful parts from the ocean of the collected data, and used algorithms to decode them and, finally, piece together the photo of the black hole on computer.
More than 200 scientists from different countries, including 16 from the Chinese mainland, worked on the EHT project for years to take the photo of the black hole. Some have asked why did the team of brilliant scientists take so long to take the photo. The answer simply is, because the task was humungous.
Since the radio telescopes used in the research have such high level of sensitivity and resolution that the data they collected were beyond imagination. For example, for five successive days in April 2017, the eight radio telescopes collected 32 gigabytes of data every second. Together, they collected about 3,500 trillion-bytes of data in five years. To get an idea of the size of the data, think of 3.5 million movies. Which means even if a person watches 10 movies a day seven days a week, he/she will take about 100 years to view them all.
EHT scientists recorded all the data on specific hard disks and then sent them to a data processing center, where the researchers adjusted the time gap between different radio telescopes and analyzed the data and finally come up with photo of the black hole.
The research team included 16 Chinese scientists, who helped process and analyze the data collected by the James Clerk Maxwell Telescope (a submillimeter-wavelength telescope at Mauna Kea Observatory in Hawai'i). Their contributions will never be forgotten.
The photo of the black hole is important, because it is the first time that we humans have "observed" black holes.
That's especially important for us physicists because we were sure about their existence thanks to theories of physics and other indirect evidence. Still, the photo is a giant leap in the history of science, not least because it allows astrophysicists and astronomers to observe a black hole.
The photo also provides solid evidence to support the general theory of relativity, which Albert Einstein propounded one century ago. According to Einstein’s theory, there are celestial bodies that have mass millions of times that of the sun and so small a radius that even light cannot escape from them. We know such celestial bodies as black holes.
Einstein was right about the point of no return, too. The black holes are such gravitational monsters that even if light strays close to them, it is lost forever — a surface which scientists call "event horizon" or point of no return.
While celebrating the success of the team of EHT researchers, let us also pay tribute to the genius of Einstein who first referred to such a celestial body 100 years ago.