The gas cloud G2

 

We have detected the gas cloud G2, a dusty, ionized gas cloud on a highly eccentric orbit around Sgr A*, which passed pericenter in spring 2014. We have discovered G2 in 2011 both from its dust and recombination line emission (Gillessen et al. 2012). We were able to predict the soon-to-come pericenter passage as well as the tidal disruption. We identified G2 in the data sets ranging back to 2002 (NACO) and 2004 (SINFONI).

 

<p><em>Time series of NACO L-band images, showing how G2 (arrow) approached the position of Sgr A* (asterisk) during the past decade.</em></p> Zoom Image

Time series of NACO L-band images, showing how G2 (arrow) approached the position of Sgr A* (asterisk) during the past decade.

 

Most spectacular is the SINFONI data, from which we extract position-velocity diagrams along the orbital path. A compilation of such diagrams shows in beautiful detail how the gravitational force of the MBH has tidally disrupted G2 - the first time that one can follow and study this process observationally.

 

<em>Time series of SINFONI position-velocity diagrams of G2. The initially compact object gets faster and more and more tidally elongated as it approaches Sgr A*. <em>From 2013 to 2015, the gas swings around the black hole onto the blue-shifted, post-peri side.</em></em>
Time series of SINFONI position-velocity diagrams of G2. The initially compact object gets faster and more and more tidally elongated as it approaches Sgr A*. From 2013 to 2015, the gas swings around the black hole onto the blue-shifted, post-peri side.

 

 

Since 2013 we have been able to see how the gas has swirled around the black hole (Gillessen et al. 2013, Pfuhl et al. 2015), with more and more gas moving from the red-shifted side of the orbit that is approaching Sgr A* over to the blue-shifted side. The data are well described by a simple model consisting only of a cloud of non-interacting test particles - the evolution is thus perfectly described by the tidal interaction.

 

 

The nature of G2 is debated. The two basic model types are purely gaseous clouds, and models that assume a central star with some circumstellar material. Our preferred model is that G2 is a dense knot in a much longer gas streamer, perhaps a stretched clump of a stellar wind, or the debris from a partial tidal disruption of a giant star that came a bit too close to Sgr A*.

 

For more information, see also the press releases A Black Hole's Dinner is Fast Approaching and Ripped Apart by a Black Hole.

 

 
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