Three shameful question of photos of a black hole

Astronomers (and all mankind) holiday: a first picture of a black hole. It was created using the Event Horizon Telescope (EHT), a virtual telescope, consisting of several radio telescopes around the world. Image shows material around the supermassive black hole at the galactic center at a distance of 55 million light-years. And yes, the black hole - a concentrated physics, crazy gravitational phenomena on the edge of the possible and the impossible, extreme conditions (for more details on how black holes are arranged, can be read here). But there are some questions.

Three shameful question of photos of a black hole

The black hole is difficult to see because it is black?

No. That is, yes. It's true: the black holes - black. Usually we see all sorts of stars and all that, because the light they emit, reaches our telescopes (or directly into our eyes), and we will register. Black holes are truly black. They do not emit visible light (due to the complex gravitational foci), so they are not visible.

But this is not a big problem. If a black hole has been in our solar system, you would have seen it. You would see the curvature of space, and its presence would have seen a substance that revolves around this funnel. If you've seen the film "Interstellar", it accurately shows the approximate visualization of the black hole - it is made with the help of astrophysicist Kip Thorne.

Black hole is difficult to see because it is tiny. Well, not so tiny as an ant, for example. She is tiny, in the sense that man is tiny, if you look at it from a distance of a kilometer. A better term would be an angular dimension. If you turn your head in a circle, you will receive all-round view of 360 degrees (but do not forget to turn the body, and the neck roll up). If you hold your thumb at arm's length, which is about half a degree angular dimension. The moon is about the same angular size, so you can cover it with your thumb. What about the size of a black hole? Yes, it is huge. And it is at a distance of 55 million light-years. This means that in order to reach the light as far as it will take 55 million years. It's incredibly far. But really prevents us from angular size. In a black hole (at least the visible part of it) of the angular size - about 40 mikroarksekund.

What is mikroarksekunda? As you know, the circle is divided into degrees (and long overdue). Each degree can be divided into 60 angular minutes and every minute - is 60 arcseconds. If we break arcseconds per million parts will mikroarksekunda. Remember that the angular size of the moon - 0, 5 degrees (when viewed from the Earth)? This means that the angular size of the Moon in 45 million times greater than the size of the black hole. A tiny black hole in terms of the angular size.

But that's not all. Because of diffraction, we can not see things tiny angular dimensions. When light passes through an opening (e.g., enters the telescope or in the eye), it dissipates. He is bent in such a way that prevents the rest of the light passing through the hole. In the case of the eye, which means that people can make out objects with an angular size of about 1 arcminutes.

And it also means that something so tiny angular dimensions, like a black hole, it is difficult to catch on a photo.

How to overcome the diffraction limit?

Let's. Things tiny angular dimensions really hard to see - how do we then see the material around the black hole? The angular resolution of the telescope actually depends on two things: the size of the hole and the wavelength of light. Using shorter wavelengths (such as ultraviolet or X-rays) gives the best resolution. But in this case the telescope uses light wavelength in the millimeter range. This rather large wavelength than visible light, which is in the range 500 nanometers. And this means that the only way to overcome the diffraction limit - make the telescope more. That is what they did with the Event Horizon Telescope. In fact, this telescope is the size of Earth. Crazy, but true. Receiving data from several telescopes in different parts of the world, you can combine data, to convert them into data with a single giant telescope. True, it is necessary to try. But with this method there is a problem. With only a few telescopes, EHT group uses several analytical methods to create the most probable picture of the data collected. So they were able to "draw" the material around the black hole.

This is really a photo of a black hole?

If you look into the telescope and see Jupiter, you actually see Jupiter. Note: If you have not already done, be sure to try. That's cool. Sunlight reflected from the surface of Jupiter, and then passes through a telescope in your eye. Boom. Jupiter. He is real.

But a black hole all a bit wrong. The image you see is not even in the visible range. This radio image created from wavelengths of light. What is the difference between radio waves and visible light, the usual? In fact, the only difference in wavelength.

Light and radio waves - electromagnetic waves. This electric field distribution changing with the changing magnetic field (simultaneously). These waves move at the speed of light - because they are the light. However, because the radio and visible light have different wavelengths, they interact differently with a substance. If you turn on the radio at home, you will receive the signal from the nearest station. These radio waves pass right through the walls. A visible - do not pass. The same applies to images. If you have a visible light from an object, you can see him with his eye and record the image on film or with a digital recorder. This image can then be displayed on the computer screen and, in fact, be considered. Like this, you can see a picture of the moon.

As for the material around the black hole, it is not a visible image. This radar image. Each pixel in the image represents a specific wavelength, but radio waves. Orange parts - a false color representation wavelength of 1 millimeter. The same thing happens when we want to "see" the image in the infrared or ultraviolet range. We need to convert these wavelengths that we can see.

So this picture of a black hole - not the usual picture. You can not see it, if you look through the telescope. But still cool. Truth? Let's discuss in our chat in the telegram.