Three embarrassing question about pictures of a black hole

Astronomers (and all mankind) holiday: presents the first snapshot of a black hole. It was created using the Event Horizon Telescope (EHT), a virtual telescope, consisting of several radio telescopes around the world. The image demonstrates the material around the supermassive black hole at the center of the galaxy at a distance of 55 million light years. And Yes, a black hole is concentrated physics, crazy gravitational phenomena on the verge of possible and impossible extreme conditions. But have a few questions.

A black hole difficult to see, because she’s black?

No. I mean, Yes. It’s true: black holes are black. Usually we see all sorts of stars and things, because of the light they emit reaches our telescopes (or in our eyes), and we recorded. Black holes really are black. They do not emit visible light (due to the complex gravitational tricks), so they are not visible.

But it’s not a big problem. If the black hole we had in the Solar system, you’d have seen it. You could see the curvature of space with her presence and I could see a substance which revolves around this hole. If you saw the movie “interstellar“, it approximately definitely shows a visualization of a black hole — it was done with the help of astrophysicist Kip Thorne.

A black hole difficult to see because it’s tiny. Well, not so tiny like an ant, for example. It’s tiny in the sense that the person is tiny when you look at it from a distance of a kilometer. The best term would be the angular size. If you turn your head in a circle, you get 360 degrees (but don’t forget to turn the body, and the neck). If you hold your thumb at arm’s length, which is about half a degree angular dimension. The moon has 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 yet it is at a distance of 55 million light years. This means that in order for the light to get that far, he will need 55 million years. It’s incredibly far away. But do we prevent the angular size. The black hole (at least its visible part) angular size — about 40 microarcsecond.

What is microarcsecond? As you know, the circle is divided into degrees (and long overdue). Each degree can be divided into 60 arc minutes, and each minute is 60 arcsecond. If arcsecond to break into a million pieces, you get microarcsecond. Remember that the angular size of the moon is 0.5 degrees (viewed from Earth)? This means that the angular size of the moon 45 million times larger than the size of a black hole. The black hole is tiny from the point of view of angular size.

But that’s not all. Due to diffraction we can’t see things the tiny angular sizes. When light passes through a hole (e.g., enters the telescope or eye), it dissipates. It’s bent in such a way that interferes with the rest of the light passing through the hole. In the case of the eye, it means that people can scan objects with an angular size of about 1 arcminute.

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

How to overcome the diffraction limit?

For example. Things tiny angular sizes it’s really hard to see how then can we see the material around the black hole? The angular resolution of the telescope really depends on two things: the size of the hole and wavelength of light. The use of smaller wavelengths (such as ultraviolet or x-rays) gives the best resolution. But in this case, the telescope uses a wavelength of light in the millimeter range. This is a fairly large wavelength compared to visible light, which is in the range of 500 nanometers.

And this means that the only way to overcome the diffraction limit is to make the telescope bigger. That is what I did with Event Horizon Telescope. In fact, it is a telescope the size of the Earth. Crazy, but true. Getting data from multiple telescopes in different parts of the world, you can combine the data to turn them into data with a single GIANT telescope. However, I have to try. But with this method there are problems. With only a few telescopes, the EHT group uses a number of analytical techniques to create the most likely image from the data collected. So they managed to “draw” the material around the black hole.

This is really a photo of a black hole?

If you look through the telescope and see Jupiter, you can actually see Jupiter. Note: if you have not done this yet, you should definitely try. It’s cool. Sunlight is reflected from the surface of Jupiter, and then passes through the telescope in your eye. Boom. Jupiter. It is real.

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

Light and radio waves is electromagnetic waves. Is the spread of the changing electric field with a changing magnetic field (at a time). These waves move at the speed of light because they are light. However, as radio and visible light have different wavelengths, they interact differently with matter. If you turn on the radio at home, you will receive the signal from the nearest radio station. These radio waves pass right through walls. And visible — not tested.

The same applies to images. If you have no visible light from the object, you can see it with your eye and record the image on film or with a digital recorder. This image then can be displayed on the computer screen and, in fact, to consider. Like so you can see the moon.

With regard to the material around the black hole, it is not the visible image. Is the radio image. Each pixel in the picture represents a specific wavelength, but radio waves. Orange is a false color representation of a wave length 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 photo is of a black hole is not an ordinary photo. You will not be able to see it if you look in the telescope. But it’s still great. Really? Let’s discuss in our chat in Telegram.

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