Astronomers understand how jets accelerate in the vicinity of supermassive black holes

(ORDO NEWS) — Narrow streams of particles, accelerated almost to the speed of light, radiate brightly and can be seen at distances of hundreds of millions and billions of light years.

Where they draw their energy from is still unknown. However, new observations have made it possible to associate such jets with the emergence of colossal shock waves.

The new IXPE space telescope has observed for the first time the polarization of X-rays from a distant blazar, a narrow stream of particles ejected by a supermassive black hole and accelerated to near-light speeds.

The work showed that this relativistic jet is accelerated enormously by shock waves that arise when it collides with the surrounding matter.

Supermassive black holes are located in the centers of large galaxies, and many of them actively absorb the surrounding matter. Falling into the hole, this substance heats up and accelerates, forming a relatively flat, spiraling disk.

Under the action of powerful magnetic fields, part of the matter is ejected from the poles of this disk in the form of narrow streams of particles accelerated to near-light speeds – relativistic jets.

Sometimes such jets accidentally turn out to be directed towards the Earth. Being at a great distance from us, they do not carry any danger, but they make the active centers of distant galaxies perfectly visible at distances of millions and even billions of light years.

Such objects are called blazars , and they radiate brightly over a wide range of wavelengths, from radio to X-rays and even gamma rays.

How exactly the acceleration of the jets occurs is not exactly clear. There are two hypotheses more widely than others. According to the first of them, they receive their colossal energy due to the reconnection of the magnetic field lines, as happens with plasma ejections on the Sun.

According to another version, the frenzied acceleration is created by shock waves arising from the collision of a jet with a slower substance surrounding its source. Such a mechanism can be compared to the movement of water, which escapes from a narrow nozzle under high pressure.

Astronomers understand how jets accelerate in the vicinity of supermassive black holes 2
The IXPE apparatus observes the Mrk 501 blazar: an artist’s view. The inner drawing shows the movement of particles through the front of the shock wave

To find out which hypothesis is correct, an international team of scientists led by Ioannis Liodakis (Ioannis Liodakis) from the University of Turku investigated the distant blazar Markarian 501 (Mrk 501), located 450 million light years away.

For observations, astronomers used the IXPE space telescope , launched into orbit less than a year ago. The peculiarity of the apparatus is precisely that it is capable of recording X-ray radiation and its polarization.

If the jet is accelerated due to magnetic reconnection, then its radiation must be polarized in the same way at all wavelengths. If the second hypothesis is correct, then the polarization of the jet radiation should depend on the wavelength.

Passing through the front of the shock wave, the particles receive a huge momentum and radiate in the X-ray range.

Moving away from it, they gradually lose energy and begin to radiate at longer and longer wavelengths. In this case, the polarization should be more pronounced in x-rays than in the less “energetic” parts of the spectrum.

By observing Mrk 501, the IXPE satellite was able to measure the polarization of a blazar’s X-ray emission for the first time.

It really turned out to be higher than that of radiation with a longer wavelength. Thus, the hypothesis that it is the shock waves that give the jets their incredible speed and brightness can be considered correct.

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