The struggle of several decades to draw a realistic black hole

We will probably have our very first image of a black hole next week. Event Horizon (EHT) telescopes have scheduled a press conference on the morning of April 10 and are expected to unveil the image of a supermassive black hole.

This will be the first time that humanity will see any of these massive objects with our own eyes, and scientists are naturally excited at the idea of ​​what the image will tell them.

Cosmic Elephants

But images of black holes have been circulating for years, right? Magazines, including this one, regularly post images of black holes alongside stories – you probably already have a mental picture of what I'm talking about. Black sphere, colorful spiral of gas … do not we already know what a black hole looks like?

Good type of. All these images are artistic representations based, sometimes loosely, on theories about what physics says about a black hole. So we have a pretty good idea of ​​what's a black hole could look like. However, the reality is that we have no confirmation. As EHT member Katie Bouman says in a TEDx talk, there may be an elephant in the center of our galaxy, as far as we know.

We will probably know the truth soon, even if it does not look like what we expected. This is for two main reasons. First, the black holes are so far that the picture will probably be much more blurred than most artistic representations. In addition, Albert Einstein's theory of general relativity tells us that space-time curves in a strange way near a black hole – a fact that artists do not explain in general.

There is another reason why black hole drawings take a certain degree of freedom, which is extremely obvious: you can not see a black hole. By definition, a black hole is a region of the space where no light escapes. No light means no picture. This means that silent black holes, those that do not suck gas or other materials, are actually invisible.

And for those who nibble matter, called active black holes, it's not a simple task either. Thick dusts gather around many active black holes, enveloping their shapes. Some betray their presence with powerful jets of matter, thousands of light-years away, though their hearts often remain hidden. The brightest of them call quasars, and it is hard to miss them. But quasars are by far the minority.

To solve these problems while maintaining a certain aesthetic sensibility, many space artists have opted for a kind of idealized black hole image. You can think of this as a black hole mat and it contains a few key components.

Black hole heating plate

First, there is the black hole itself, the sphere or void in the center of any black hole image. In reality, it is a kind of negative image, an object defined by its absence. The curved edge of the superheated gas we see defines the outer limit of a singularity, the horizon of events of the black hole beyond which escape is impossible. The bubble of darkness that this edge touches is the present singularity.

Then there is the cloud of dust and gas itself, called the accretion disk. Of course, all black holes do not have them, but if we want a real picture, we need to have a way to contrast the black hole. The accretion disk is formed much in the same way as the rings of Saturn: the material attracted inward by the gravity of the black hole begins to orbit and eventually flatten into a thin disc.

"It is very common for material to flow in the form of a disc to the black hole," says Erin Kara, a Hubble Postdoctoral Fellow at the University of Maryland. "We have heard that they are sucking all around them, but in fact, the hot gases will first turn around the black hole, and then over time, they will overtake it. horizon of events – this point of no return, which creates the "shadow" in the middle of the image. "

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10 things you do not know about black holes

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You can also see black holes with what looks like massive beams of light coming from each side, perpendicular to the accretion disk. These jets are called relativistic jets and consist of superheated plasma ejected from the accretion disk. Jet is one of the most powerful phenomena in the known universe; they travel at a significant speed of light and can span thousands of light-years from the black hole itself. Only the largest and most active black holes will create jets, although in some cases they may be quite spectacular. Quasars, extremely powerful black holes in the center of galaxies, can shine louder than the entire Milky Way.

Now back to the black hole mat. The standard formula is usually the following: black sphere, glossy disc, maybe some jets. But that's not how a black hole would really appear to us. For a more scientific realism, things must start to get weird.

Hand drawn origins

Let's move on to a different image of the black hole, made possible by the most powerful force: the magic of the Hollywood movie. Gargantua, the black hole presented in the movie "Interstellar", is distinctly different from the black holes typical of science articles. The image was made with the help of theoretical physicist Kip Thorne and better describes what a black hole might look like, even if it is not perfect.

The obvious thing that distinguishes Gargantua is the presence of what seems to be two rings, instead of just one. The double discs are due to the extraordinarily strong force of gravity near a black hole, so strong that it curves the path of light. What we see is actually a simple accretion disk, engraved in two by gravity. From our point of view, even at the equator, light coming from the back of the disc will be pulled up and over the black hole, giving the appearance of a second ring in an arc above black hole. Likewise, the light coming from the bottom of the back half of the disc will be bent under the black hole and directed towards us.

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The puzzling simplicity of black holes

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The picture varies depending on the angle under which we see the black hole. For example, the higher one raises above the plane of the disc, the smaller the ring will appear because the effect of the bending of the light is all the weaker.

It lacks, however, an important element to the "interstellar" black hole, something that the director Christopher Nolan knew well, but chose to leave aside to make a more comprehensible representation. The type of black hole shown by the film is surrounded by a disc of material that rotates very quickly around the black hole.

In fact, the gas and dust move so fast that the photons that come out of it would be altered by the Doppler effect. It's the same phenomenon that makes sirens go up when they come and go when they get away from us. The waves, bright or sonorous, moving towards us seem to have a higher frequency because they are crushed together, and conversely for those who move away. Thus, a swiveling drive from left to right would appear much brighter and more blue on the left side and darker and darker on the other. Gargantua seems equally brilliant on both sides (the colors are not always represented in black hole images), which makes it a bit false.

A more precise vision of a black hole with a fine accretion disk was created more than 40 years ago by an astrophysicist named Jean-Pierre Luminet. The drawing is based on calculations he made in 1978 using an old IBM punch card computer. Then he took the data obtained and drew by hand the simulated black hole on a photographic negative with a pen and ink. He then took a negative to get the picture below.

The theoretical black hole created by Luminet is shiny on the left and attenuated on the right according to the Doppler effect. The back is curved and the bottom is almost completely invisible, masked by the brilliant disk in front. The photo is surprisingly similar to the one created by Thorne and some colleagues following the release of "Interstellar" to provide a more accurate description of what Gargantua should have looked like.

The real thing

The actual image of the black hole that we will get from the EHT will not look like any of these images. The resolution will be much worse, on the one hand, and the parameters of two of the black holes they examined – Sagittarius A * and M87 – might be different. The size and shape of the accretion disk around a black hole, the plasma temperature surrounding it, the speed of rotation, if the black hole itself is rotating, l & # 39; 39 angle of view and many other factors could create a different look image than we expect.

And who knows, maybe they will find something totally unexpected. There could be an elephant hiding in our galaxy after all.