Black holes gather a huge mass in a single point. Nowhere else do such powerful gravitational fields act. Such a phenomenon of the universe deserved to be photographed, but it was not until a few years ago that we finally saw what they are like, beyond their representation in science fiction movies about space.
We finally have direct proof of the existence of black holes thanks to the international effort of the Event Horizon Telescope, EHT. Thirteen institutions came together to create the Event Horizon Telescope , with the support of different entities. The bulk of the funding came from the US National Science Foundation (NSF), the European Research Council (ERC) and various organizations in East Asia.
First image of a black hole
The Event Horizon Telescope (EHT), a global array of eight ground-based radio telescopes operating as part of an international collaboration, was designed to image a black hole.
Black Hole (EHF)
In April 2019, the first direct visual evidence for the existence of a supermassive black hole and its shadow was presented. Specifically, it is an image of a supermassive event located 55 million light years away , in the center of Messier 87, a massive galaxy that inhabits Virgo, a cluster of galaxies close to us. It had a mass 6.5 billion times that of our Sun.
Black holes are extraordinary cosmic objects, characterized by having enormous mass in a very compact size. The presence of these objects affects their surroundings in extreme ways, warping space-time and superheating all surrounding material.
Its existence was already intuited in the precepts of the general relativity theory of Albert Einstein, who considered that the idea of a black hole was too absurd to be real. Through this photograph, it was possible to corroborate their existence.
How to photograph black holes?
The technique to achieve this seemingly simple photograph is not so simple. If embedded in a luminous region, such as a disk of glowing gas, the black hole is expected to cast a dark, shadow-like area.
Using different imaging and calibration methods, the presence of a circular structure around a dark area —the black hole’s shadow—was revealed in multiple independent EHT observations.
The EHT observations use a technique known as very long baseline interferometry (VLBI). In this way, telescopes around the world are synchronized and take advantage of the rotation of our planet to create a large virtual telescope the size of the Earth that observes at a wavelength of 1.3 mm.
The individual telescopes involved are: ALMA, APEX, the IRAM 30-meter Telescope (Pico Veleta, Sierra Nevada, Granada, Spain), the IRAM NOEMA Observatory (French Alps), the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope and the Greenland Telescope (GLT).
Location of some of the telescopes that make up the EHT. Credits: ESO / L. Calçada
Although the telescopes that make up the EHT are not physically connected, they are capable of synchronizing the data they record with atomic clocks, the hydrogen masers, which time their observations precisely.
