The gas streamer G1-2-3 in the Galactic center

Vol. 707
6. Interstellar and circumstellar matter

The gas streamer G1-2-3 in the Galactic center

This paper reports the discovery and characterization of a third compact gas clump, following the previously known objects G1 and G2, moving on nearly identical, highly eccentric orbits around the Galactic center black hole, Sgr A*. The odds of finding three separate stars on such similar orbits by chance are vanishingly small (about 1 in 500,000). Instead, the evidence points to these clouds originating from stellar winds produced by IRS 16SW, a massive binary star system orbiting in the same plane. The key clue is that the small differences between the three orbits change at a rate matching the orbital motion of IRS 16SW itself. Each cloud contains just a few Earth masses of gas and passes within about 100 AU of the black hole. G2 made its closest approach in 2014, while G2t will not reach that point until 2031. As these clouds swing past the black hole, they experience drag from the surrounding accretion flow, losing kinetic energy in a measurable way that helps constrain the density of material feeding Sgr A*. New hydrodynamic simulations show that if IRS 16SW's stellar wind has velocities lower than previously assumed, the wind can indeed form dense clumps through interactions with the surrounding medium. These clumps could provide most of the fuel currently powering the black hole's faint emission.