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

S. Gillessen, F. Eisenhauer, J. Cuadra, R. Genzel, D. Calderon, S. Joharle, T. Piran, D. C. Ribeiro, C. M. P. Russell, M. Sadun Bordoni, A. Burkert, G. Bourdarot, A. Drescher, F. Mang, T. Ott, G. Agapito, A. Agudo Berbel, A. Baruffolo, M. Bonaglia, M. Black, R. Briguglio, Y. Cao, L. Carbonaro, G. Cresci, Y. Dallilar, R. Davies, M. Deysenroth, I. Di Antonio, A. Di Cianno, G. Di Rico, D. Doelman, M. Dolci, S. Esposito, D. Fantinel, D. Ferruzzi, H. Feuchtgruber, N. M. Förster Schreiber, A. M. Glauser, P. Grani, M. Hartl, D. Henry, H. Huber, C. Keller, M. Kenworthy, K. Kravchenko, J. Lightfoot, D. Lunney, D. Lutz, M. Macintosh, F. Mannucci, D. Pearson, A. Puglisi, S. Rabien, C. Rau, A. Riccardi, B. Salasnich, T. Shimizu, F. Snik, E. Sturm, L. J. Tacconi, W. Taylor, A. Valentini, C. Waring, M. Xompero

TL;DR

The paper presents evidence for a third gas clump, G3, moving on an orbit nearly identical to previously observed G1 and G2, forming a coherent gas streamer G1-2-3 around Sgr A*. The authors argue that a purely stellar origin is statistically unlikely for three co-moving clumps and favor a wind-fed origin from the binary IRS16SW, a view supported by the close alignment of orbital elements and their time evolution with IRS16SW’s motion. Through joint orbital fitting in a fixed potential and with drag, they derive a common orbital plane and similar semi-major axes and eccentricities, placing G3’s pericenter after G2 by roughly two decades and indicating a synchronized orbital phase. Hydrodynamic simulations with reduced wind velocities from IRS16SW reproduce Earth-mass-scale clumps and show feasible pathways for delivering gas to the central black hole, reinforcing the scenario that IRS16SW winds can supply Sgr A* with gas via clump formation and subsequent drag.

Abstract

The black hole in the Galactic Center, Sgr A*, is prototypical for ultra-low-fed galactic nuclei. The discovery of a hand-full of gas clumps in the realm of a few Earth masses in its immediate vicinity provides a gas reservoir sufficient to power Sgr A*. In particular, the gas cloud G2 is of interest due to its extreme orbit, on which it passed at a pericenter distance of around 100 AU and notably lost kinetic energy during the fly-by due to the interaction with the black hole accretion flow. 13 years prior to G2, a resembling gas cloud called G1, passed Sgr A* on a similar orbit. The origin of G2 remained a topic of discussion, with models including a central (stellar) source still proposed as alternatives to pure gaseous clouds. Here, we report the orbit of a third gas clump moving again along (almost) the same orbital trace. Since the probability of finding three stars on close orbits is very small, this strongly argues against stellar-based source models. Instead, we show that the gas streamer G1-2-3 plausibly originates from the stellar wind of the massive binary star IRS16SW. This claim is substantiated by the fact that the small differences between the three orbits - the orientations of the orbital ellipses in their common plane as a function of time - are consistent with the orbital motion of IRS 16SW.

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

TL;DR

The paper presents evidence for a third gas clump, G3, moving on an orbit nearly identical to previously observed G1 and G2, forming a coherent gas streamer G1-2-3 around Sgr A*. The authors argue that a purely stellar origin is statistically unlikely for three co-moving clumps and favor a wind-fed origin from the binary IRS16SW, a view supported by the close alignment of orbital elements and their time evolution with IRS16SW’s motion. Through joint orbital fitting in a fixed potential and with drag, they derive a common orbital plane and similar semi-major axes and eccentricities, placing G3’s pericenter after G2 by roughly two decades and indicating a synchronized orbital phase. Hydrodynamic simulations with reduced wind velocities from IRS16SW reproduce Earth-mass-scale clumps and show feasible pathways for delivering gas to the central black hole, reinforcing the scenario that IRS16SW winds can supply Sgr A* with gas via clump formation and subsequent drag.

Abstract

The black hole in the Galactic Center, Sgr A*, is prototypical for ultra-low-fed galactic nuclei. The discovery of a hand-full of gas clumps in the realm of a few Earth masses in its immediate vicinity provides a gas reservoir sufficient to power Sgr A*. In particular, the gas cloud G2 is of interest due to its extreme orbit, on which it passed at a pericenter distance of around 100 AU and notably lost kinetic energy during the fly-by due to the interaction with the black hole accretion flow. 13 years prior to G2, a resembling gas cloud called G1, passed Sgr A* on a similar orbit. The origin of G2 remained a topic of discussion, with models including a central (stellar) source still proposed as alternatives to pure gaseous clouds. Here, we report the orbit of a third gas clump moving again along (almost) the same orbital trace. Since the probability of finding three stars on close orbits is very small, this strongly argues against stellar-based source models. Instead, we show that the gas streamer G1-2-3 plausibly originates from the stellar wind of the massive binary star IRS16SW. This claim is substantiated by the fact that the small differences between the three orbits - the orientations of the orbital ellipses in their common plane as a function of time - are consistent with the orbital motion of IRS 16SW.

Paper Structure

This paper contains 12 sections, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observed properties of G2
  3. Source models for G2
  4. Observations
  5. Analysis
  6. The orbits of G1, G2 and G3
  7. Position velocity diagram for G3
  8. Discussion
  9. Conclusions
  10. Data
  11. Orbital elements
  12. Additional illustration

Figures (5)

  • Figure 1: G3 in the ERIS integral-field data from summer 2024. Top left: Continuum image showing the S-stars. Top right: Background-subtracted line map centered at $2.173\,\mu$m, corresponding to Brackett-$\gamma\, + 1000\,$km/s. G3 stands out. Bottom left: Example of a pixel selection (on - green, off - red) for extracting the G3 spectrum overlaid on the continuum map. Bottom right: The resulting spectrum shows a strong emission line at $2.173\,\mu$m.
  • Figure 2: The orbits and data of G1, G2 and G3, fit under the side constraint that they share the same orbital plane, semi-major axis and eccentricity. Top: On-sky appearance of the two orbits. Middle: The radial velocities. Bottom: The spatial coordinates as a function of time. The non-Keplerian shapes are a result of the drag force acting on G2 and G3 when they are close to Sgr A*.
  • Figure 3: Left: Position-velocity diagram extracted from the summer-2024 data cube, using a curved slit along the orbital trace of G3. The emission of G3 is concentrated around $(-300\,\mathrm{mas},+1000\mathrm{km/s})$. Like G2, G3 seems to be followed by a tail, indicative of even more material flowing along the G1-2-3 path. Right: For comparison, the same diagram for G2 extracted from the 2008 data cube (from 2019ApJ...871..126G).
  • Figure 4: Snapshots of the hydrodynamic simulations of the Wolf-Rayet stars (white asterisks) feeding Sgr A* (white disk) in the central parsec. The maps show density square integrated along the the line of sight in square root scale, i.e. $[\int\rho^2dz]^{1/2}$, represeting the expected Brackett-$\gamma$ flux. Each panel represents a simulation run varying the wind speed of IRS 16SW: 300 km s$^{-1}$ (top), 400 km s$^{-1}$ (bottom left), and 600 km s$^{-1}$ (bottom right). The production of clumps on the scale shown here is dominated by IRS16 SW. Snapshots created with Splash 2007PASA...24..159P.
  • Figure 5: Alternative representation of the combined orbit fit for G1, G2 and G3. The data from G1 and G3 have been corrected for the differences in the respective orbits to the G2 orbit, and plotted on top of the G2 orbit and data.