Probing the gas density in our Galactic Centre: Moving mesh simulations of G2

Elad Steinberg*, Re'em Sari, Orly Gnat, Stefan Gillessen, Philipp Plewa, Reinhard Genzel, Frank Eisenhauer, Thomas Ott, Oliver Pfuhl, Maryam Habibi, Idel Waisberg, Sebastiano von Fellenberg, Jason Dexter, Michi Bauböck, Alejandra Jimenez Rosales

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


The G2 object has recently passed its pericentre passage in our Galactic Centre. While the Brγ emission shows clear signs of tidal interaction, the change in the observed luminosity is only of about a factor of 2, in contention with all previous predictions. We present high-resolution simulations performed with the moving mesh code, RICH, together with simple analytical arguments that reproduce the observed Brγ emission. In our model, G2 is a gas cloud that undergoes tidal disruption in a dilute ambient medium. We find that during pericentre passage, the efficient cooling of the cloud results in a vertical collapse, compressing the cloud by a factor of ~5000. By properly taking into account the ionization state of the gas, we find that the cloud is UV starved and are able to reproduce the observed Brγ luminosity. For densities larger than ≈500 cm-3 at pericentre, the cloud fragments due to cooling instabilities and the emitted radiation is inconsistent with observations. For lower densities, the cloud survives the pericentre passage intact and its emitted radiation matches the observed light curve. From the duration of Brγ emission that contains both redshifted and blueshifted components, we show that the cloud is not spherical but rather elongated with a size ratio of 4 at year 2001. The simulated cloud's elongation grows as it travels towards pericentre and is consistent with observations, due to viewing angles. The simulation is also consistent with having a spherical shape at apocentre.

Original languageAmerican English
Pages (from-to)1841-1849
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Jan 2018

Bibliographical note

Publisher Copyright:
© 2017 The Authors.


  • Accretion
  • Accretion discs
  • Galaxy: centre


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