Signatures of planets and protoplanets in the Galactic center: a clue to understand the G2 cloud?

TL;DR

This paper explores the emission signatures of rogue planets and protoplanets near the Galactic center, proposing that photoevaporated protoplanets could explain the G2 cloud's observed luminosity.

Contribution

It introduces a model for detecting rogue planets and protoplanets in the Galactic center and suggests photoevaporated protoplanets as a potential explanation for G2.

Findings

Photoevaporation of protoplanets can produce luminosities similar to G2.

Rogue planets are unlikely to be detected unless tidally disrupted.

Proposes G2 might be a tidally stripped protoplanet.

Abstract

Several hundred young stars lie in the innermost parsec of our Galaxy. The super-massive black hole (SMBH) might capture planets orbiting these stars, and bring them onto nearly radial orbits. The same fate might occur to planetary embryos (PEs), i.e. protoplanets born from gravitational instabilities in protoplanetary disks. In this paper, we investigate the emission properties of rogue planets and PEs in the Galactic center. In particular, we study the effects of photoevaporation, caused by the ultraviolet background. Rogue planets can hardly be detected by current or forthcoming facilities, unless they are tidally disrupted and accrete onto the SMBH. In contrast, photoevaporation of PEs (especially if the PE is being tidally stripped) might lead to a recombination rate as high as ~10^45 s^-1, corresponding to a Brackett-gamma luminosity ~10^31 erg s^-1, very similar to the observed luminosity of the dusty object G2. We critically discuss the possibility that G2 is a rogue PE, and the major uncertainties of this model.