New observations of the gas cloud G2 in the Galactic Center

TL;DR

This paper reports new observations of the gas cloud G2 near the Galactic Center, confirming its highly elliptical orbit, increased velocity gradient, and the detection of its tail, with no hydrodynamic effects observed yet.

Contribution

The study provides updated orbital parameters of G2, including a higher eccentricity and refined pericenter timing, and confirms the absence of hydrodynamic effects in the observed data.

Findings

G2 has an eccentricity of 0.966.

Velocity gradient of G2 reached 600 km/s in 2012.

No hydrodynamic effects detected so far.

Abstract

We present new observations of the recently discovered gas cloud G2 currently falling towards the massive black hole in the Galactic Center. The new data confirm that G2 is on a highly elliptical orbit with a predicted pericenter passage mid 2013. The updated orbit has an even larger eccentricity of 0.966, an epoch of pericenter two months later than estimated before, and a nominal minimum distance of 2200 Schwarzschild radii only. The velocity gradient of G2 has developed further to 600 km/s FWHM in summer 2012. We also detect the tail of similar total flux and on the same orbit as G2 along the trajectory at high significance. No hydrodynamic effects are detected yet, since the simple model of a tidally shearing gas cloud still describes the data very well. The flux of G2 has not changed by more than 10% between 2008 and 2012, disfavoring models where additional gas from a reservoir is released to the disrupting diffuse gas component.