The Event Horizon telescope revealed the magnetic field lines around the middle black hole of M87.

In 2019, astronomers captured the first direct picture of a dark hole. This was a picture of the supermassive black hole in the core of M87. And when a lot of people saw him, their reaction was, "Is that right?" This is understandable, considering that the image is only a fuzzy dot in the shape of a donut. That's not a big thing to watch. But an astronomical image is a small fraction of the information that astronomers collect. Recently, more of this data has been analyzed, such as the polarization of light and the magnetic field surrounding the black hole.

Polarization is a fundamental property of light, along with wavelengths or intensity. If you think of light as a wave oscillating through space, then polarization is the orientation of this oscillation. Light waves can oscillate upward and downward, to the left and the right, or even swirl clockwise or outwards. When the light comes from a hot source, such as the material surrounding a black hole, many polarizations are mixed so that the light is basically non-polarized. But when light passes through the ionized gas, different polarizations interact with the gas to a greater or lesser extent. Consequently, the light which reaches Earth is polarized. By studying the polarisation of light in the vicinity of the M87 black hole, we can learn more about the surrounding matter.

In the case of radio astronomy, there is also a polarised light source called synchrotron radiation. This happens when the electrons are trapped by the magnetic field and move along the field lines in tight coils. The polarization of the radiation of the synchrotron provides information about the orientation of the magnetic field lines.

What is interesting, however, is that most of the light observed is not polarised. Only approximately 15 percent of the light is polarized. Most of the light coming out of the black hole is not polarised. This is unexpected because the ionized gas near the black hole would have to be strongly magnetized, so we would expect that the light coming to us would be strongly polarized. What happened to that?

It seems that gas near the black hole is magnetized, but rather than having a magnetic structure that is large and simple, the magnetization is a chaotic jumble at smaller scales. The scale at which the magnet is randomly oriented is below the resolution of the Event Horizon telescope. Things get a little fuzzy. All small-scale polarisations fade to give the impression that they are not polarized.

Results like these are important because they give us a huge overview of the materials and magnetic fields in the vicinity of the black holes. As we understand more, we will be able to complex processes that create active black holes and how they interact with the surrounding galaxy. All this information is buried in the data, and that's more than what's going on.