Ever since humans began to look up at the stars, they have been curious about the vastness of the universe, and this is still the case today. With the help of various observation devices, modern humans can take a large number of photos of the deep space of the universe, which are updated almost every day.

This photograph, the first human photograph of a black hole, was published on 10 april 2019 by the sight telescope collaboration and is of a supermassive black hole at the centre of galaxy "M87" - " M78*", a black hole about 6.5 billion times the mass of the sun, about 55 million light-years from earth.

This direct imaging of m78* has helped to confirm the existence of strange objects such as black holes in the universe, and to validate einstein's general theory of relativity (scientists have found that the observed shadow of the black hole is almost identical to that predicted by the general theory of relativity). Relativity predicted), which is of considerable importance to human cosmology.

It is worth noting that "M78*" Is not the only target of the eht, according to a release from the european southern observatory, the vision telescope, which took the first pictures of a black hole, will announce a major discovery on 12 may 2022 at 13:00 (utc). What exactly is this "Major discovery"? For the moment we can only speculate.

Past research has shown that there is a very bright and dense source of radio waves at the centre of the milky way - the constellation sagittarius* - although the general consensus in the scientific community is that "Sagittarius a*" Is supposed to be a supermassive black mass. " Should be a supermassive black hole, this is, after all, only a hypothesis indirectly inferred from observational data.

(figure shows a star moving near "Sagittarius a*" In 2018)

In fact, there are still scientists who believe that "Sagittarius a*" Is not a supermassive black hole, for example, on 21 may 2021, a team of researchers from the international centre for relativistic astrophysics in italy published a paper in the monthly notices of the royal astronomical society stating that "Sagittarius a*" Has sagittarius a*" Is possibly just a special kind of dark matter clump.

In other words, to confirm whether there is a supermassive black hole at the centre of the milky way or not, we need further evidence, in contrast to the hint given by the european southern observatory about what the eht will announce on 12 may: "This is a major, groundbreaking discovery related to the milky way".

On this basis, and given the field of observation in which the sphere telescope specialises, it is reasonable to assume that this "Major discovery" Will be the eht's direct imaging of sagittarius a* (like the first human photographs of a black hole), and that if this is the case, it would mean that the secret of the centre of the galaxy is about to be revealed.

Compared to the aforementioned "M78*", "Sagittarius a*" Has a much smaller mass, about 4.3 million times the mass of the sun, and if "Sagittarius a*" Is indeed a black hole, then it is a black hole. If sagittarius a* is indeed a black hole, then its apparent diameter is only 50 microarcseconds, what is this concept? If a person could see a newspaper on the earth from the moon, the apparent diameter of the full stop at the end of the text on the newspaper would be about 1 microarcsecond.

(the apparent diameter, also known as the apparent size, is simply understood to be the angle of view of the object we see, and the farther away the object is from us, the smaller its apparent diameter)

Nonetheless, the apparent field telescope is still capable of directly imaging sagittarius a*, which in simple terms is an array of observational facilities such as radio observatories or radio telescopes located around the world.

As shown above, these observing facilities are integrated by a technique known as ultra-long baseline interferometry to form a virtual telescope with high sensitivity and high angular resolution, bearing in mind that the larger the diameter of a telescope, the higher its resolution.

From a technical point of view, even if sagittarius a* were a black hole, the telescope would still be able to "See" It, or to be more precise, "See" The shadow of the black hole. Normally, matter captured by a black hole falls into the black hole in a spiral orbit, where it is accelerated to near the speed of light by the gravitational force of the black hole (due to the conservation of angular momentum), and where the violent friction releases a large number of electromagnetic waves, which outline the shadow of the black hole.

If the above speculations are correct, then the secret of the centre of the galaxy is about to be revealed by the eht: Is there a supermassive black hole there or not? And if so, what does it actually look like? This is really something to look forward to.