Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets

¹ Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstrasse 25/8, 620 Innsbruck, Austria
e-mail: awismari@gmail.com
² Department of Astronomy, Faculty of Mathematics, University of Belgrade, Studentski trg 16, 11000 Belgrade, Serbia
e-mail: andjelka@matf.bg.ac.rs
³ Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica, 00133 Rome, Italy
e-mail: amedeo.balbi@roma2.infn.it

Received: 15 November 2018
Accepted: 12 February 2019

Abstract

Context. The detailed evolution of exoplanetary atmospheres has been the subject of decade-long studies. Only recently, investigations began on the possible atmospheric mass loss caused by the activity of galactic central engines. This question has so far been explored without using available exoplanet data.

Aims. The goal of this paper is to improve our knowledge of the erosion of exoplanetary atmospheres through radiation from supermassive black holes (SMBHs) undergoing an active galactic nucleus (AGN) phase.

Methods. To this end, we extended the well-known energy-limited mass-loss model to include the case of radiation from AGNs. We set the fraction of incident power ɛ available to heat the atmosphere as either constant (ɛ = 0.1) or flux dependent (ɛ = ɛ(F_XUV)). We calculated the possible atmospheric mass loss for 54 known exoplanets (of which 16 are hot Jupiters residing in the Galactic bulge and 38 are Earth-like planets, EPs) due to radiation from the Milky Way’s (MW) central SMBH, Sagittarius A* (Sgr A*), and from a set of 107 220 AGNs generated using the 33 350 AGNs at z < 0.5 of the Sloan Digital Sky Survey database.

Results. We found that planets in the Galactic bulge might have lost up to several Earth atmospheres in mass during the AGN phase of Sgr A*, while the EPs are at a safe distance from Sgr A* (>7 kpc) and have not undergone any atmospheric erosion in their lifetimes. We also found that the MW EPs might experience a mass loss up to ~15 times the Mars atmosphere over a period of 50 Myr as the result of exposure to the cumulative extreme-UV flux F_XUV from the AGNs up to z = 0.5. In both cases we found that an incorrect choice of ɛ can lead to significant mass loss overestimates.