The first image of a black hole, published last year, was a milestone in the study of astronomy. Since then, physicists have been striving to learn as much as possible about this phenomenon. In March, a study concluded that around the event horizon there is an infinite series of rings of light, gradually sharper, caused by extreme gravitational curvature. Now, the researchers in this study believe that these photon rings can tell the story of the universe.
Michael Johnson of the Harvard Smithsonian Center for Astrophysics compares these circles to the growth rings on a tree: count how many rings are drawn on the trunk and you will know how old the tree is. In the case of black holes, the circles correspond to pictures from a film that shows the evolution of the cosmos from that point of view.
Black hole M87, the first recorded in a direct image. Image: EHT Collaboration / Reproduction
EHT images (Event Horizon Telescope) or accretion disk (the yellow and orange part) and the shadow of the black hole (the dark center). We cannot see the photon rings, as they are very thin and the resolution is not high enough. But if we could see it, that ring of photons would be the fingerprint of the black hole - its size and shape encode the black hole's mass and rotation.
"The set is similar to the frames of a film, capturing the history of the universe visible from the point of view of the black hole," says Johnson. Watching the “movie” can reveal important information about black holes and the nature of gravity.
However, there is a limit: each ring is only six days older than the previous one, and eventually they pass through the black hole's event horizon and are devoured. "We are not going to see dinosaurs," jokes Johnson.
From where we are, about 55 million light years away, we cannot see these rings in detail. To image the M87, telescopes around the world worked together to create a single telescope the size of Earth, but even so, EHT observations allow the calculation of black hole masses within 10% or more of the actual value.
However, removing the project from Earth can change things significantly. “Although capturing images of black holes normally requires many distributed telescopes, photon rings can be studied using only two telescopes that are very far apart. Adding a space telescope to the EHT would be sufficient, ”says Johnson.
This additional telescope would have to go a little further than Earth's low orbit. A good position would be to place a telescope on the Moon. To further improve the resolution, a third party could go even further, beyond the Moon, into a stable position between the Sun and the Earth.
"Even in geosynchronous orbit, it would already be a great improvement in resolution for the EHT", says Johnson, referring to the space band about 35,2 thousand kilometers above the Earth's surface. "If we go to the Moon, I think we would be really looking at an entirely new science."
Observing the photon rings in an extended EHT can be a much easier task. “We came out of this situation where it was unimaginable to increase the resolution of the images by a factor of two. And now we are thinking of increasing the EHT resolution by a factor of 100 ”, adds the researcher.