ASTRO In the literature: partially resolved

How do black hole jets keep cluster cores from cooling?

In plain words

Gas at the centers of galaxy clusters radiates away its heat in less than a billion years, yet it forms stars at only a few percent of the expected rate. Jets from the central black hole carry enough energy, but how that energy spreads evenly through the gas is not known.

Precise statement

In cool-core clusters the central gas has cooling time $t_{\mathrm{cool}}<1\ \mathrm{Gyr}$ within $\sim 100\ \mathrm{kpc}$, while star formation rates are $\sim 1\text{-}10\ \mathrm{percent}$ of classical cooling-flow rates of $10^2\text{-}10^3\ M_{\mathrm{sun}}/\mathrm{yr}$. Determine how jet mechanical power $P_{\mathrm{jet}}\sim 10^{44}\text{-}10^{46}\ \mathrm{erg/s}$ is converted to heat nearly isotropically: weak shocks, sound waves, turbulent dissipation, cosmic-ray heating, or turbulent mixing. The answer is the heating rate per channel versus radius matched to the cooling rate.

What would settle it

High-resolution X-ray spectroscopy of gas velocities and temperatures in cluster cores (XRISM and successors) combined with simulations reproducing the measured velocity structure and the heating balance.

Status in the literature

Unverified note

Jet cavity energetics match the cooling luminosity; Hitomi in 2016 measured a line-of-sight velocity dispersion of about $1.6x10^{7}\,\mathrm{cm}/\mathrm{s}$ in the Perseus core, and XRISM has been measuring cluster core velocities since 2024.