Breath of a Quasar: How a Black Hole Controls a Cluster ✛

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295 000 meters per second. Not even particles in solar coronal ejecta move that fast. But at the center of the galaxy cluster H1821+643, hot gas does exactly that. The quasar at its heart takes a breath, and its breath stirs everything around for 60 thousand light-years.

This is not poetic exaggeration but a direct consequence of the supermassive black hole's activity. The mechanism: as it swallows matter, it accelerates some of it to near-light speeds and ejects it back into space. Such a wind, driven by the active galactic nucleus, can punch through its host galaxy and spill far into the interstellar medium. But until recently, astronomers could not measure its influence on such scales.

The result was stunning: in the quiet Perseus cluster, the same iron line is half as wide. Here, the ions scatter at an average of 295 km/s — 130 km/s faster. Simple gravitational infall could not produce such a spread. Instead, the shock wave from the quasar wind, slamming into the rarefied gas, generates plasma turbulence — a chaos of vortices that the lines capture.

The fraction of kinetic energy in this turbulence is 8% of the thermal energy. And the total energy injected into the gas during the quasar's active periods reaches 10% of its luminosity. A few percent — seems small at first. But it is exactly enough to offset the cooling of the gas via radiation. Computer numerical simulations of galaxy evolution like IllustrisTNG required precisely this efficiency, and now it has been found in reality.

Thus, the quasar's breath becomes the regulator of life for an entire galaxy cluster. Without it, the gas would cool and collapse toward the center, triggering an avalanche of star formation. Instead, the quasar 'breathes' steadily, keeping the ionized medium hot and rarefied for billions of years. And each new exhalation is captured by the shift of narrow lines — a breath that can not only be heard but also seen in spectra.