Because black holes absorb all the light and matter around them, we can't see black holes because there's no light coming to Earth. In April 2017, however, a study found that black holes were observed successfully. Because black holes themselves absorb all the material and absorb all the light, it's impossible to observe, but how could they be observed? The first thing that made black holes known to the world was Einstein's general theory of relativity, that if the mass of a star is compressed in a small space, it would create a powerful, gravity-driven celestial body that could not escape even light. And of course, at that time, Einstein's genius was not recognized, and he believed that the celestial sphere, which had enormous gravity that couldn't escape even the fastest material in the world, existed only in theory, but not in existence. As astrophysics evolved over time, scientists became aware that black holes were inevitable. In 1969, a black hole was discovered by a physicist in the U.S. and the name was even defined. But it's only estimated. It's not observed. So scientists have given evidence that they observe and exist through X-rays generated by black holes. Now, technological advances have allowed us to observe black holes through the shadow of black holes. In more detail, the gravitational pull of the black hole, through radio waves and light that pass through it, which is not absorbed, is the principle that allows the ducting of the black hole to be seen. In this way, we analyzed the data and we were able to estimate the appearance of the black hole, and we were able to reveal it to the world for the first time in April 2019. And just to give you a quick overview of how black holes are formed, stars are able to generate light energy through fusion, and through that energy, they are able to overcome the pressures of the outer universe and maintain volume. But when we run out of the resources for fusion, we can't resist the enormous pressure from the outer universe, and the black hole at the center is spread out in all directions by a supernova explosion on the outside. Through this shape, the mass is 5 to 15 times the sun, but the radius is only 15 to 45 kilometers long, which is newly born as a heavenly creature. And then we've been getting more and more external materials and energy, and we've been able to create more powerful gravity and absorb a little bit more distant external materials and energy, and we've been growing that size more and more infinitely. Scientists recommend that there are about 400 million black holes in the Milky Way alone, although they haven't been found yet.