Taking a photo of a black hole, once considered impossible, has become reality, as astronomers worldwide successfully captured the first-ever event horizon of the M87, a black hole at the center of the Virgo A galaxy of and presented the results in simultaneous press conferences around the world on Wednesday.
Chinese space experts hailed the event as a milestone, and said it is the most direct evidence of the existence of the black hole.
“The image reveals the black hole at the center of M87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5-billion times that of the Sun,” according to a EHT press release sent to the Global Times late on Wednesday.
The results of the international collaboration under a project codenamed Event Horizon Telescope (EHT) were presented simultaneously at a press conference at the Shanghai Astronomical Observatory with the Chinese Academy of Sciences (CAS), at 9pm Wednesday [13:00 Universal Time], one of the seven designated international research bodies. Others included Greenland Telescope Denmark in Lyngby, Denmark and the US National Science Foundation in Washington, DC.
The black hole, as indicated by its name, is so dark that taking a photo of it is impossible. Because the pull of gravity of the black hole is so immense that nothing escapes, not even electromagnetic radiation such as X-rays, light and radio waves, it makes our direct detection of the object impossible, according to the Dubai-based Science Alert website.
Although we cannot see the extremely dark object, by taking a photo of its “shade,” we can better understand the black hole, verify its existence, and even calculate its approximate diameter, Jiao Weixin, a space science professor at Peking University, told the Global Times on Wednesday.
The EHT is an international collaboration to pursue a long-standing goal in astrophysics to directly observe the immediate environment of a black hole with angular resolution comparable to the event horizon, according to the EHT website.
To achieve that, the EHT has been adopting a technique known as the very-long-baseline interferometry (VLBI), linking radio dishes across the world to create an Earth-sized interferometer in order to measure the size of the emission regions of the two super-massive black holes with the largest apparent event horizons: Sagittarius A* at the center of our galaxy, the Milky Way and M87 at the center of the Virgo A galaxy.
Only by forming such an Earth-sized interferometer–that is to say, to turn all radio telescopes located across the globe to look in the same direction–to all focus one single object at one time, we can achieve such a high resolution, powerful enough to actually see the curves of light in space, the inner ring of which is the event horizon, and to conclude that the center of such curved light is the black hole itself, Jiao noted.
The more distant these radio telescopes are, the better angular resolution they can get—meaning, a clearer capture of the distant object, Chen Xuelei, a research fellow with the CAS National Astronomical Observatories in Beijing, told the Global Times on Wednesday.
Chen noted that, although such an Earth-sized interferometer is the best we can use at present, it is possible in the future to have extraterrestrial satellite-boasting large-scale radio telescopes in space to achieve better angular resolution for the study of black holes.
VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds — enough to read a newspaper in New York from a sidewalk cafe? in Paris, according to the EHT press release.
Rather than an optical photo, the visual material achieved through the interferometer would be a model based on data and calculations, Chen said.
Shen Zhiqiang, head of the Shanghai Astronomical Observatory, said there are eight telescopes in six EHT array sites around the world, including the South Pole Telescope in the South Pole, and James Clerk Maxwell Telescope in Hawaii.
Shen said although the Shanghai-based Tianma Telescope is not a member of the EHT project, the East Asia VLBI network, consisting of the Tianma Telescope and radio telescopes in South Korea and Japan, carried out a large number of 22 GHz and 43 GHz mapping monitors before and after the EHT observation, which contributed to the EHT results.
“World’s first ever black hole photo has gathered some 190 million readings on China’s twitter-like Sina Weibo, and nearly 800,000 comments as of 10 pm, just about one hour following the worldwide simultaneous press conferences for the EHT discovery event.
16 Chinese scientists participated in the discovery of the photo.