Astronomers (and all mankind) have a holiday: the first picture of a black hole is presented. It was created using the Event Horizon Telescope (EHT), a virtual telescope made up of several radio telescopes around the world. The image shows material around a supermassive black hole at the center of a galaxy 55 million light-years away. And yes, a black hole is concentrated physics, crazy gravitational phenomena on the verge of the possible and the impossible, extreme conditions (you can read more about how black holes work here). But there are several questions.
Is a black hole hard to see because it's black?
Not. That is, yes. It's true: black holes are black. Usually we see all sorts of stars and everything, because the light that they emit reaches our telescopes (or directly into our eyes), and we register it. Black holes are really black. They do not emit visible light (due to complex gravitational tricks), so they cannot be seen.
But this is not a big problem. If we had a black hole in our solar system, you would see it. You would see the curvature of space by its presence and you would see the substance that revolves around this funnel. If you've seen the movie Interstellar, it roughly shows a visualization of a black hole - it was done with the help of astrophysicist Kip Thorne.
The black hole is difficult to see because it is tiny. Well, okay, not as tiny as an ant, for example. She is tiny in the sense that a person is tiny when viewed from a distance of a kilometer. The best term would be angular size. If you turn your head in a circle, you will get a 360-degree all-round view (but remember to turn your body too, otherwise you will bend your neck). If you keep your thumb at arm's length, that's about half a degree angular size. The moon has about the same angular size, so you can cover it with your thumb.
What about the size of the black hole? Yes, it is huge. It is also 55 million light years distant. This means that it will take 55 million years for light to travel this far. It's incredibly far away. But the angular size really prevents us. A black hole (at least its visible part) has an angular size of about 40 microarseconds.
What is a microarxsecond? As you know, the circle is broken down into degrees (and has been for a long time). Each degree can be broken into 60 arc-minutes, and each minute is 60 arc seconds. If you divide an arcsecond into a million parts, you get a microarsecond. Remember that the angular size of the moon is 0.5 degrees (as viewed from Earth)? This means that the angular size of the moon is 45 million times larger than the size of a black hole. The black hole is tiny in terms of its angular size.
Promotional video:
But that is not all. Due to diffraction, we cannot see things of tiny angular sizes. When light passes through an opening (for example, through a telescope or into the eye), it is scattered. It bends in such a way that it interferes with the rest of the light passing through the hole. In the case of the eye, this means that people can make out objects with an angular size of about 1 arc minute.
And that also means that something as tiny as a black hole is difficult to capture in a photo.
How to overcome the diffraction limit?
Let's admit. Things of tiny angular dimensions are really hard to see - how then are we to see the material around a black hole? The angular resolution of a telescope really depends on only two things: the size of the hole and the wavelength of the light. Using shorter wavelengths (such as ultraviolet or X-ray radiation) gives better resolution. But in this case, the telescope uses the wavelength of light in the millimeter range. This is quite a long wavelength compared to visible light, which is in the 500 nanometer range.
And this means that the only way to overcome the diffraction limit is to make the telescope bigger. That is, what they did with the Event Horizon Telescope. Basically, it's a telescope the size of the Earth. Madness, but true. By collecting data from multiple telescopes in different parts of the world, you can combine the data to turn it into data from one GIANT telescope. True, you have to try. But there are problems with this method too. With only a few telescopes, the EHT team uses a number of analytical techniques to create the most likely image from the collected data. So they managed to "draw" material around the black hole.
Is this a real photo of a black hole?
If you look through a telescope and see Jupiter, you are actually seeing Jupiter. Note: If you haven't done this yet, be sure to give it a try. That's cool. Sunlight bounces off Jupiter's surface and then travels through a telescope into your eye. Boom. Jupiter. He's real.
But with a black hole, things are a little different. The image you are seeing is not even in the visible range. This is a radio image created from the wavelengths of light. What is the difference between radio waves and ordinary visible light? In fact, the difference is only in the wavelength.
Light and radio waves are electromagnetic waves. This is the propagation of a changing electric field along with a changing magnetic field (simultaneously). These waves travel at the speed of light - because they are light. However, since radio and visible light have different wavelengths, they interact with matter differently. If you turn on the radio at home, you will receive a signal from the nearest radio station. These radio waves travel right through the walls. And the visible ones do not pass.
The same goes for images. If you have visible light from an object, you can see it with your eye and record this image on film or with a digital recorder. This image can then be displayed on a computer screen and, in fact, viewed. This is how you can see a picture of the moon.
As for the material around the black hole, this is not a visible image. This is a radio image. Each pixel in the image represents a specific wavelength, but radio waves. The orange portions are false color representations of the 1 millimeter wave. The same happens when we want to "see" an image in the infrared or ultraviolet range. We have to convert these wavelengths to what we can see.
So this shot of a black hole is no ordinary photograph.
Ilya Khel