Image of the black hole Sagittarius A*, in the center of the Milky Way. EHT/EFE
More than a decade ago, some of the greatest experts on the planet realized that if they wanted to unravel the mystery behind black holes, they would have to work together.
The Event Horizon Telescope (EHT) is actually a network of telescopes in various parts of the world that have joined forces to take for the first time a picture of Sagittarius A*, the supermassive black hole in the center of the Milky Way, our galaxy.
More than 300 scientists, 80 institutions and eight observatories in the United States, Spain, Chile, Antarctica and Mexico participated.
"It was an opportunity that I could not miss," says Gisela Ortiz (Oaxaca, 34 years old), an astrophysicist at the National Autonomous University of Mexico (UNAM), who joined the project five years ago.
Sagittarius A*, read Sagittarius A star, is a monster that concentrates four million times the mass of the sun and is 26,000 light years from Earth.
Ortiz admits that it is difficult to measure its size with the objects that are known on the planet.
"I don't have a good analogy," he is honest.
How was it possible to capture a black hole, which emits no light and swallows everything that is close enough to it?
“When we see the photograph, we are looking at the light emitted by the gas around the black hole,” explains Ortiz.
The electromagnetic waves of that light are picked up by telescopes on our planet.
These signals arrive as numbers or coordinates of the celestial body and thanks to computational algorithms they can be translated into images.
The EHT explains that these data were obtained after several nights of observation,
Interferometry is a technique used in astronomy to join various signals received by each of these observatories around the world and obtain a single image with higher resolution.
“These are instruments operated in different countries and for this reason, only thanks to an international collaboration were we able to achieve this result”, points out the specialist.
Mexico was invited to participate because it has the Alfonso Serrano Large Millimeter Telescope, the world's largest mobile single-dish telescope.
The instrument is located on top of the Sierra Negra volcano, in Puebla, at an altitude of more than 4,600 meters.
Ortiz comments that in the country there is a very small group of specialists who do science with this technology.
“Speaking of the very long baseline interferometry technique,
One of the most complicated parts for the project collaborators was making sure that the signal received by a telescope in Antarctica and another, thousands of kilometers away, in Puebla, was exactly the same so that they could be added together.
“Because they are so far apart, there is a kind of delay in the time that signal arrives,” says Ortiz.
"It's a slow process, combining the signals is just the first step," he adds.
The data was received by each observatory and then sent to Massachusetts (USA) and Bonn (Germany) for processing.
In the words of the scientist, "they are cleaned" in order to gradually form this image.
The Mexican astronomer Gisela Ortiz in a file photo.Gaceta Unam
Until three years ago, practically everything that was known about black holes was represented in theoretical terms and in very complex equations.
In 2019, the EHT managed to capture the first image of M87, a black hole that is even bigger and even further away: with a mass of 6 billion suns and more than 50,000 light years away.
"These objects were predicted theoretically and there were also studies that suggested that there was a black hole in all the centers of the galaxies, but it had remained at that", comments the scientist.
Until very recently, they have finally been able to be observed.
"These findings verify that this theory is correct and that black holes are not just a mathematical object, but an object that is in the center of each galaxy," adds Ortiz.
Paradoxically, taking the picture of Sagittarius A* has been more complicated.
Being smaller than M87*, the glowing gas swirling around the so-called event horizon, the black hole's gateway, moves faster.
What takes weeks to go around in M87*, in Sagittarius A* takes only minutes.
The Spanish astronomer José Luis Gómez compared it to a little boy who does not stay still to appear in the photo.
Another factor was his location.
"We are looking towards a part of the sky where we are affected by the material that is in our line of sight, gas and very small dust particles that interfere with the signals that we receive in our telescopes," added Ortiz.
“That makes the presented image of the black hole look blurry,” he adds.
In the photograph you can see these rings of light because the black hole has an enormous mass and exerts a force of gravity so great that it is capable of "bending light", explains the specialist.
"It's not something we're used to seeing here on Earth," she notes, "the black hole distorts space-time, the light from the gas around it bends and forms circular paths around the hole."
After the objects cross the so-called event horizon, that border between the universe and the interior of the black hole, it is not known what happens to them.
"That's why they are so enigmatic, they are mysterious objects because we don't fully understand what happens inside them," says Ortiz.
This huge monster for the proportions of the Earth is, however, very small compared to the size of the galaxy.
And that opens another question: why an entire galaxy revolves around a black hole.
"It's amazing to think of these objects that ultimately rule the universe," she says.
Ortiz, who is a physicist and obtained her master's and doctorate in Sciences from UNAM, was part of another international team that in 2020 published the discovery of a planet similar to Saturn, 35,000 light years from Earth.
"Mexico's radio astronomy is recognized internationally," she says.
The researcher, who is doing her post-doctorate in Germany, hopes that the new EHT discovery can give a boost to the scientific community dedicated to studying the universe and so that scientists abroad can return to the country to share knowledge with that are starting
"This can start a new era, especially for the new generations of Mexican astronomers," she concludes.
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