We now know why black hole jets emit high-energy radiation

Active galactic nuclei, fueled by the supermassive black holes they contain, are the brightest objects in the universe. The light originates from jets of material that are ejected at nearly the speed of light from the environment surrounding the black hole. In most cases, these active galactic nuclei are called quasars. But on rare occasions, when one of the jets is pointed directly at Earth, it’s called a blazar, and it appears much brighter.

While the general outline of how the blazar works has been drawn up, many details are still poorly understood, including how fast-moving matter generates so much light. Now, researchers have turned a new space observatory called the X-ray Polarizing Imaging Explorer (IXPE) toward one of the brightest flames in the sky. Taken together, the data from this and other observations indicate that light is produced when black hole jets collide with slow-moving matter.

Planes and light
IXPE specializes in detecting the polarization of high-energy photons, the direction of vibrations in the electric field of light. The polarization information can tell us something about the processes that created the photons. For example, photons originating from a disordered environment will have essentially random polarizations, while a more ordered environment tends to produce photons with a limited range of polarizations. Light passing through materials or magnetic fields can also change its polarization.

This has been shown to be useful in the study of blazars. The high-energy photons that these objects emit are generated by the charged particles in the jets. When these objects change trajectory or slow down, they have to give up energy in the form of photons. Because they move at close to the speed of light, they have a lot of energy to give up, allowing blazars to emit everything from radio waves to gamma rays, some of which stay in those cells. energies despite billions of years of redshift. .


So the question is what makes these particles slow down. There are two main ideas. One such factor is that the aircraft environment is turbulent, with chaotic accumulations of materials and magnetic fields. This causes the particles to slow down and a chaotic environment will mean that the polarization becomes largely random.

An alternative idea involves a shock wave, where material from the jets collides with slowly moving material, slowing it down. This is a relatively ordered process, producing a relatively narrow band bias that becomes more pronounced at higher energies.

Enter IXPE
The new set of observations is a coordinated campaign to record Blazar Markarian 501 using a variety of telescopes capturing polarization at longer wavelengths, with IXPE handling the highest energy photons. In addition, the researchers searched the archives of several observatories for previous observations of Markarian 501, which allowed them to determine whether the polarization was stable over time.

In general, across the entire spectrum, from radio waves to gamma rays, the measured polarizations were within a few degrees of each other. It was also stable over time, with its alignment increasing at higher photon energies.

There is still a small difference in polarization, indicating a relatively slight disturbance at the collision site, which is not really a surprise. But it is much less turbulent than one would expect for turbulent matter with complex magnetic fields.

While these results provide a better understanding of how black holes produce light, this process ultimately depends on the production of jets, which occur close to the black hole. It’s still not really understood how these jets form, so people studying the astrophysics of black holes still have reason to get back to work after the weekend.

nature2022. DOI: 10.1038 / s41586-022-05338-0 (About DOIs).