The Properties and Fate of the Galactic Center G2 Cloud

TL;DR

This study models the G2 cloud near the Galactic Center, fitting observational data with a magnetically arrested cloud scenario, and predicts its emission and impact on Sgr A* during pericenter passage.

Contribution

It presents a detailed photoionized cloud model for G2, fitting multi-epoch data and revising predictions of its emission and influence on the black hole.

Findings

Best-fit cloud parameters: density 1.8e5 cm^-3, radius 2.2e15 cm, mass 4 Earth masses.

Radio and X-ray emissions are below detection thresholds, consistent with observations.

Larger cloud mass could increase accretion and brighten Sgr A*.

Abstract

The object G2 was recently discovered descending into the gravitational potential of the supermassive black hole (BH) Sgr A*. We test the photoionized cloud scenario, determine the cloud properties, and estimate the emission during the pericenter passage. The incident radiation is computed starting from the individual stars at the locations of G2. The radiative transfer calculations are conducted with CLOUDY code and $2011$ broadband and line luminosities are fitted. The spherically symmetric, tidally distorted, and magnetically arrested cloud shapes are tested with both the interstellar medium dust and $10$~nm graphite dust. The best-fitting magnetically arrested model has the initial density $n_{\rm init}=1.8\times10^5{\rm cm}^{-3}$, initial radius $R_{\rm init}=2.2\times10^{15}{\rm cm}=17 {\rm mas}$, mass $m_{\rm cloud}=4M_{\rm Earth}$, and dust relative abundance $A=0.072$. It provides a good fit to $2011$ data, is consistent with the luminosities in $2004$ and $2008$, and reaches an agreement with the observed size. We revise down the predicted radio and X-ray bow shock luminosities to be below the quiescent level of Sgr A*, which readily leads to non-detection in agreement to observations. The magnetic energy dissipation in the cloud at the pericenter coupled with more powerful irradiation may lead to an infrared source with an apparent magnitude $m_{L'}\approx13.0$. No shock into the cloud and no X-rays are expected from cloud squeezing by the ambient gas pressure. Larger than previously estimated cloud mass $m_{\rm cloud}=(4-20)M_{\rm Earth}$ may produce a higher accretion rate and a brighter state of Sgr A* as the debris descend onto the BH.