We have seen Black Holes in the cinema and in countless illustrations, but none of those images was real. They were only artistic approaches to an astronomical phenomenon so strange, remote and massive that we had never been able to photograph it until now.
Albert Einstein in 1915 was the first to imagine the impossible, the spatiotemporal singularity that we know today as black holes. Since then we have studied these phenomena indirectly, through different types of measurements of constants present in the cosmos.
The image you have on these lines looks like a ring of fire, but it is a supermassive black hole located in the center of the galaxy M87, in the Virgo cluster, 55 million light years from Earth. The estimated diameter of the event horizon of this monster is 40,000 million kilometers and it has 6,500 million times the mass of our Sun. It is one of the most massive black holes we know.
The bright orange halo seen around the black hole is a colossal cloud of incandescent gas that heats up as it falls on the event horizon.
How has this image been obtained?
Actually, it is not a photograph in the strict sense of the word. The event horizon of a black hole cannot be photographed in a conventional way because it does not emit light, it absorbs it. What you are seeing are the effects of gravity on radio waves that emit matter in an area just above the event horizon.
The gravity of the black hole deforms the fabric of time-space and generates a circular shadow that delimits the black hole itself. That’s what the astronomers of the Event Horizon Telescope project have captured, a network of radio telescopes that have been synchronized by atomic clocks to become a “camera” the size of our planet.
Dozens of observatories around the world have collaborated to obtain the image, from China to the North Pole, from the United States to Europe. The scientific procedure is called very long base interferometry (VLBI) and it consists of matching the light frequency data of pairs of observatories. The petabytes of resulting data have been analyzed by a team of 200 astrophysicists to achieve this pioneering image that reconstructs radio waves to form a visible image for us.
How do we know what a black hole is?
Because the characteristics of the image adapt perfectly to the simulations and physical predictions made so far on the black hole in M87. There are still years of work ahead, but this first image shows two things. The first is that black holes are a reality beyond the numbers of astrophysics. The second is that if scientists from all over the world collaborate, there is no limit to what we can achieve. One day, in short, historical for science. [ ESO ]