Tue. Apr 23rd, 2019

So it 'photographs' a black hole | Science

So it 'photographs' a black hole | Science

Take out one Photo A black hole is not easy: black holes have such gravity that nothing can escape their attraction, not even light, and if a ray of light (or anything else) falls inside, it can not come out again. How to photograph something that does not emit, nor can it reflect light? To be fair, we do not photograph the hole, but the light that is around it interacting with it, just before passing the edge of no return. This light offers us the background to get to see the hole by contrast: a black sphere enveloped by light that falls attracted by its brutal gravitational field.

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As if that were not enough, although it is a supermassive object, it is very compact and far away; seen from Earth it looks small. It's as difficult as trying to photograph an orange on the surface of the Moon: you need a telescope as big as the Earth itself to get the necessary magnifications for the photo.

This is what the project has achieved Event Horizon Telescope. By joining telescopes located all over the world, a technique known as interferometry, it is possible to add the data from eight radio telescopes to simulate a super telescope as large as the separation between the antennas, our own planet.

Network of telescopes of the Event Horizon Telescope, the separation between them allows to simulate a super telescope as big as our own planet. / EHT

Even so, from the black hole photo we only have a few data, as if we had only information from a few dozen pixels or points from a photo of thousands. The rest of the photograph should be constructed between combining the known data and what we expect to see.

To make the simulations of how the hole should be seen, the new chips of the graphic cards used by the players played a fundamental role. gammers, ideal for this purpose. The same researchers have assured that without this technology coming from leisure these simulations would not have been possible: from computer games we have reached the last line of astrophysics research.

From left to right, simulation of how it should look, areas that sweep the telescopes of the EHT project during the rotation of the Earth and the final image. / EHT

With special software, the image is composed based on the data received and what is expected to be seen in the simulations. Of course to avoid that the reference of "what we hope to see" contaminates the algorithm, control parts are included, some as curious as the images of Katie Bouman's Facebook, of the EHT project. The program is so good that by introducing an elephant in the center of the galaxy, with just a few dozen pixels the program reconstructs something very similar. The reliability of the technique is surprising.

In the photo we can see a kind of luminous half moon, but the most interesting part is in what is not seen, the black hole is the dark circle that surrounds the arc of light. This circle is the horizon of events; Anything that crosses this line will fall irretrievably into the gravitational well with no possibility of going out, including light. It is all that is possible to approach a black hole.

It's as difficult as trying to photograph an orange on the surface of the Moon

The light that forms the curious crescent moon is not trivial either. We can see more light on one side because it is a rotating black hole and as it rotates it drags the light rays with it, accumulating more light on one side than on the other.

Unfortunately we do not see all the parts, the jets that come out of the black hole perpendicular to its rotation are missing. These are due to the materials that fall into the black hole at high speed colliding with each other, causing a part to be fired at high speed and directed by the powerful magnetic fields of the object, something similar to the jets that come out of an orange if we press it until it breaks the skin. This part will have to be left for a new photo.

Borja Tosar is an astrophysicist


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