If you are reading this column, then you should like astronomy. If you like astronomy, then you must have seen an incredible image of a supermassive black hole in the center of the M87 galaxy, which was very successful in 2019.
She is still more amazing. In an image released yesterday, the Horizon Event Telescope (EHT) team showed magnetic field lines on accretion disks around the black hole, providing very important clues to its physical functioning.
To recall, M87 is a galaxy about 50 million light years away. At its center, a black hole approximately 7 billion times the mass of the Sun produces a jet that is launched at a distance of 5,000 light years. The dimensions of the body, even larger, for the supermassive black hole made it an excellent target for EHT.
The observatory is actually a combination of radio telescopes around the Earth. Spanning multiple continents, combining all the signals seen by each of its antennas, the system acts like a telescope that is the size of a planet. In this way, they are able to obtain excessive observational power, being able to see the details of the case around the black hole.
This creates the case for what we call the extensional disk. This disc, mainly composed of small particles of hydrogen gas and interstellar dust, acts as a “food” for the black hole, swallowing and contributing to its development.
Previous results showed only the intensity of light emitted by the disk, not to mention much about the other properties. But now the team was able to use the information about the polarization of the emitted light.
Polarization is the direction of vibration of photons. Although this may sound complicated, it is the principle used by many sunglasses, which block polarized light in one direction and only allow light in the other direction to reach our eyes.
In the case the polarized light indicates the direction and intensity of the magnetic field in the disk, and it is necessary for us to understand how the black hole works. In particular, it is the magnetic field that produces powerful jets that can send particles thousands of light-years away.
The researchers also compared the data with the results of relativistic magnetohydrodynamic simulations (which, as its name implies, explain how magnetic fields behave).
The conclusion is that most models are not consistent with the data, except that magnetic fields fall very close to the “edge” of the black hole. These regions then prevent matter from falling into the black hole so easily, and emanate the jet from the black hole.
Thus, observations are important because they help researchers to dismiss various hypotheses and reinforce a model of strong magnetic fields on the surface of a black hole.
The team hopes to get better results in other radiofrequencies as well, but already with incomplete analysis, as the polarization levels at these other frequencies should be even higher.
What about our black hole?
Many people ask: What about the black hole in the center of the Milky Way, Dhanu A *? After all, it is 25,000 light years away, not 50 million.
Observations were made, but the analysis here is much more complex. Because it is a relatively small black hole, which is a thousand times smaller than the one in M87, it is like a flea that bounces back and forth all the time.
This variability makes image processing very difficult, as it is not in the same place every time. I am hoping that this image will be revealed soon.