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The year 2019 has arrived. We have thus promised a splendid moment in astronomy. For years, the Event Horizon telescope has been striving to bring us the very first telescopic photography of the black hole event horizon.
Indeed, despite all their popularity in the public imagination, we have never actually seen a black hole. And the reason is ridiculously simple.
You see that black holes are literally invisible. The attraction of their gravity is so immense that beyond a certain point, nothing escapes. This includes electromagnetic radiation – such as X-rays, infrared, light and radio waves – that would allow us to detect the object directly.
This point of no return is called the horizon of events. In addition to being a terrifying place in which you never want to end up, it's also our key to visualizing a black hole.
Although we may not be able to see the black hole itself, there is a chance that its event horizon can be photographed; and we're about to see the results with the Event Horizon Telescope (EHT), which must be announced publicly every day.
Update (April 5, 2019): It seems that the day has arrived! On April 10, 2019, the team behind the EHT project and associated organizations will present the results that they describe as "groundbreaking", and we will cover the live action.
But long before the EHT, there was an astrophysicist named Jean-Pierre Luminet. Until 1978, he had already given us what could be considered the very first image of the event horizon of a black hole.
This is not, of course, a real photo. Luminet, who had a background in mathematics, used his skills to make the first computer simulation of what a black hole might look like, using a 1960s IBM 7040 card-punch computer.
"At the time, it was a very exotic subject and most astronomers did not believe in their existence," Luminet told ScienceAlert.
"I wanted to explore the strange physics of black holes and propose specific mechanisms that could help to obtain indirect signatures of their very existence.In addition, to continue the wordplay, with my name" Luminet ", I have much liked the idea of the bright star can give rise to observable phenomena. "
What data has the computer returned? Luminet then carefully traced the plot by hand to pen and Chinese ink on negative paper, as if it were a human printer.
This blurred image – seen above – shows what a flat disk falling in a black hole might look like if we were close enough to see it. It does not seem flat, because the intense gravity of the black hole bends the light around it.
"Indeed, the gravitational field curves the light rays near the black hole to the point of revealing the back of the disc," Luminet explained in an article published on arXiv last year.
"The curvature of the light rays also generates a secondary image that allows us to see the other side of the accretion disk, on the opposite side of the black hole of the observer."
Luminet was the first, but he was not the only one to be captivated by the mystery of what a black hole might look like. Others have since tried to visualize these objects and have even put their efforts on the big screen.
InterstellarThe black hole of Gargantua. (Paramount Pictures)
The film of Christopher Nolan 2014 Interstellar was praised for its allegedly "scientifically accurate" description of a black hole, based largely on the work conducted by Luminet decades ago, and created in consultation with theoretical physicist Kip Thorne of Caltech.
In the end, the film opted for a simplified version, to be less confusing and pretty on the screen.
It was certainly impressive. but, according to Luminet and Thorne, it's not really what a black hole would look like.
The primary and secondary images created by the gravitational field are present and correct. But unlike the Luminet image, the brightness of the disc is uniform.
A simulation of a black hole from an article by Thorne and his colleagues on CG techniques used to develop Gargantua. (James et al., Classical and Quantum Gravity)
"It is precisely this strong asymmetry of apparent luminosity," writes Luminet, "which is the main signature of a black hole, the only celestial object capable of giving the internal regions a disk of Acceleration a rotation speed close to the speed of light and induce a very strong Doppler effect. "
He wrote a 15-page article on the science of film, and Thorne himself wrote a book on the subject.
You may notice that all these versions of a black hole are very different from another type of black hole picture that you may have seen, especially for the discovery of LIGO in 2016 .
These are based on the work of astrophysicist Alain Riazuelo, of the French National Center for Scientific Research and the International Astronomical Union, which simulated for the first time such a black hole in 2016.
The reason why these black holes look different is that the work shows a black hole at rest – a hole without accretion disk.
Stripped of this shroud of dust and gas, the gravity of the black hole distorts the space behind him; if we were close enough to see the black hole like this, we would be moving, captured by gravity in orbit. That's why it seems to move through the field of stars.
As in the video LIGO, in the case of two black holes together, each black hole has a small, banana-shaped secondary image of the other hole that appears behind it. (The gravity is cared for.)
EHT is focused on the Sagittarius A *, the supermassive black hole in the center of our own galaxy, the Milky Way.
We do not know what we are going to see. it is possible that the data only returns a few fuzzy pixels. (If this is the case, several telescopes will join the collaboration and the scientists will try again.)
Since the black hole had an accretion disk during the observations, we anticipate something that looks a lot like the work of Luminet.
In addition, we hope that this collaboration will help us better understand the polarization of the radiation, the structure of the magnetic field and the relativistic jets of the black hole. He has already given clues about the structure of the space around the black hole.
But what is the most exciting part of the work of ISE? We are totally with Luminet on this one.
"The photo of the accretion disk!" he said. And we can hardly wait.
A version of this article was published for the first time in January 2019.
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