The impact of supermassive black holes on exoplanet habitability: I. Spanning the natural mass range

TL;DR

This study addresses how SMBH-driven winds from active galactic nuclei can impact exoplanet habitability across galaxies by varying BH mass from 10^5 to 10^10 solar masses and considering planets up to 150 kpc from galactic centers. Using an adapted ultrafast outflow wind model, the authors compare energy-driven and momentum-driven winds and compute heating, molecular speeds, atmospheric escape, and ozone depletion for Earth-like atmospheres with nitrogen- and hydrogen-dominated compositions. The main findings show that atmospheric heating, mass loss, and ozone depletion increase with SMBH mass and are strongest near the galactic center, with energy-driven winds generally more destructive; for BH masses above roughly 10^8 solar masses, ozone can be depleted near completely within inner kiloparsecs, potentially rendering planets uninhabitable. The work highlights that SMBH growth history can shape galactic habitability and provides a framework for integrating more detailed radiative and chemical processes in future analyses.

Abstract

While the influence of supermassive black hole (SMBH) activity on habitability has garnered attention, the specific effects of active galactic nuclei (AGN) winds, particularly ultrafast outflows (UFOs), on planetary atmospheres remain largely unexplored. This study aims to fill this gap by investigating the relationship between SMBH mass at the galactic center and exoplanetary habitability, given that SMBH masses are empirically confirmed to span approximately 5 orders of magnitude in galaxies. Through simplified models, we account for various results involving the relationships between the distance from the planet to the central SMBH and the mass of the SMBH. Specifically, we show that increased SMBH mass leads to higher atmospheric heating and elevated temperatures, greater molecular thermal velocities, and enhanced mass loss, all of which diminish with distance from the galactic center. Energy-driven winds consistently have a stronger impact than momentum-driven ones. Crucially, ozone depletion is shown to rise with SMBH mass and decrease with distance from the galactic center, with nearly complete ozone loss ($\sim100\%$) occurring across galactic scales for SMBHs $\geq 10^8 M_\odot$ in the energy-driven case. This study emphasizes that SMBH growth over cosmic time may have produced markedly different impacts on galactic habitability, depending on both the mass of the central black hole (BH) and the location of planetary systems within their host galaxies.

Figures (10)

• Figure 1: Increase in atmospheric temperature caused by AGN wind as a function of the mass of the central galactic SMBH in Solar masses. The left panel shows the energy-driven case, while the right one shows the effect of momentum-driven winds. The lines represent the distance $R$ from the Galactic Center (in kpc). The labels N$_2$ and H$_2$ indicate the main element of planetary atmospheric composition, molecular nitrogen and hydrogen.
• Figure 2: Increase in atmospheric temperature caused by energy- and momentum-driven AGN wind as a function of the distance to the Galactic center (in kpc). The labels $\text{N}_2$ and $\text{H}_2$ indicate the main element of planetary atmospheric composition, molecular nitrogen and hydrogen.
• Figure 3: Most probable velocity of molecules in the planetary atmosphere ($v_{\text{mp}}$) by energy- and momentum driven AGN wind as a function of the mass of the central galactic SMBH in Solar masses. The left panel shows the energy-driven case, while the right one shows the effect of momentum-driven winds. The lines represent the distance R from the Galactic Center (in kpc). The labels $\text{N}_2$ and $\text{H}_2$ indicate the main element of planetary atmospheric composition, molecular nitrogen and hydrogen. The horizontal line represents the escape velocity of the Earth ($v_{\text{esc}} \approx 11.2\,\mathrm{km\,s^{-1}})$.
• Figure 4: Most probable velocity of molecules in the planetary atmosphere ($v_{\text{mp}}$) by momentum and energy-driven AGN wind as a function of the distance to the central galactic SMBH (in kpc). The labels $\text{N}_2$ and $\text{H}_2$ indicate the main element of planetary atmospheric composition, molecular nitrogen and hydrogen. The horizontal line represents the escape velocity of the Earth ($v_{\text{esc}} \approx 11.2\,\mathrm{km\,s^{-1}}$).
• Figure 5: Atmospheric mass loss (relative to Earth’s atmospheric mass) due to wind-mediated escape as a function of the mass of the central galactic SMBH in Solar masses. The left panel shows the energy-driven case, while the right one shows the effect of momentum-driven winds. The lines represent the distance $R$ from the Galactic Center (in kpc).