Detection of a Drag Force in G2's Orbit: Measuring the Density of the Accretion Flow onto Sgr A* at 1000 Schwarzschild Radii

Gillessen, S.; Plewa, P. M.; Widmann, F.; Fellenberg, S. D. von; Schartmann, M.; Habibi, M.; Rosales, A. Jimenez; Bauböck, M.; Dexter, Jason; Gao, F.; Waisberg, I.; Eisenhauer, F.; Pfuhl, O.; Ott, Thomas; Burkert, Andreas; Zeeuw, P. T. de; Genzel, R.

doi:10.3847/1538-4357/aaf4f8

Cited by 68 publications

(81 citation statements)

References 69 publications

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“…First, our simulations reproduce the total X-ray luminosity observed by Chandra (Baganoff et al 2003), meaning that we capture at least a majority of the hot, diffuse gas at large radii. Second, our simulations reproduce the r −1 density scaling inferred from observations that were taken over a large radial range (Gillessen et al 2019), implying that we are capturing a majority of the gas at all radii and that our inflow/outflow rates have the right radial dependence. Third, our simulations can reproduce the magnitude of the RM of both the magnetar (produced at r 0.1 pc, Eatough et al 2013) and Sgr A* (produced at r 10 −4 pc, Marrone et al 2007), demonstrating that our calculated magnetic field strengths are reasonable at both small and large scales.…”

Section: Introductionsupporting

confidence: 57%

“…Several viable models have been proposed, including those that appeal to strong outflows (Blandford & Begelman 1999) and those that appeal to convective instabilities that trap gas in circulating eddies (Stone, Pringle & Begelman 1999;Narayan, Igumenshchev & Abramowicz 2000;Quataert & Gruzinov 2000b;Igumenshchev & Narayan 2002;Pen, Matzner & Wong 2003). The range of models corresponds to a dependence of density on radius between the two extremes of r −3/2 and r −1/2 , with the combination of multiple observational estimates at ∼ 7 different radii supporting r −1 in the inner regions of the flow (Gillessen et al 2019) with a potential break near the Bondi radius (Wang et al 2013). Another key consideration is the angular momentum of the gas being fed at large radii.…”

Section: Introductionmentioning

confidence: 99%

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The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

Ressler

Quataert

Stone

2019

Monthly Notices of the Royal Astronomical Society

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We study the flow structure in 3D magnetohydrodynamic (MHD) simulations of accretion onto Sagittarius A* via the magnetized winds of the orbiting Wolf-Rayet stars. These simulations cover over 3 orders of magnitude in radius to reach ≈ 300 gravitational radii, with only one poorly constrained parameter (the magnetic field in the stellar winds). Even for winds with relatively weak magnetic fields (e.g., plasma β ∼ 10 6 ), flux freezing/compression in the inflowing gas amplifies the field to β ∼ few well before it reaches the event horizon. Overall, the dynamics, accretion rate, and spherically averaged flow profiles (e.g., density, velocity) in our MHD simulations are remarkably similar to analogous hydrodynamic simulations. We attribute this to the broad distribution of angular momentum provided by the stellar winds, which sources accretion even absent much angular momentum transport. We find that the magneto-rotational instability is not important because of i) strong magnetic fields that are amplified by flux freezing/compression, and ii) the rapid inflow/outflow times of the gas and inefficient radiative cooling preclude circularization. The primary effect of magnetic fields is that they drive a polar outflow that is absent in hydrodynamics. The dynamical state of the accretion flow found in our simulations is unlike the rotationally supported tori used as initial conditions in horizon scale simulations, which could have implications for models being used to interpret Event Horizon Telescope and GRAVITY observations of Sgr A*.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

Ressler

Quataert

Stone

2019

Monthly Notices of the Royal Astronomical Society

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“…While G2 is tidally interacting during its closest approach to Sgr A* 10 , the dust component of G2 has remained unresolved. The emitting gas is unbound at closest approach 10 , but that is not inconsistent with the existence of a stellar mass keeping the dust emission compact 8 . Several models have been proposed to account for G2 in terms of an optically thick distribution of dust surrounding a star: a young, low-mass star (T Tauri star) that has retained a protoplanetary disk 25 (scenario 1) or that generates a mass-loss envelope 26 (scenario 2); or, the merger of a binary system 9,24,27 (scenario 3).…”

Section: Flux Measurementsmentioning

confidence: 94%

A population of dust-enshrouded objects orbiting the Galactic black hole

Ciurlo

Campbell

Morris

et al. 2020

Nature

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Nature volume 577, pages337-340 (2020) https://www.nature.com/articles/s41586-019-1883-yThe central 0.1 parsecs of the Milky Way host a supermassive black hole identified with the position of the radio and infrared source Sagittarius A* (refs 1,2 ), a cluster of young, massive stars (the S stars 3 ) and various gaseous features 4,5 . Recently, two unusual objects have been found to be closely orbiting Sagittarius A*: the so-called G sources, G1 and G2. These objects are unresolved (having a size on the order of 100 astronomical units, except at periapse where the tidal interaction with the black hole stretches them along the orbit) and they show both thermal dust emission and line emission from ionized gas 6-10 . G1 and G2 have generated attention because they appear to be tidally interacting with the supermassive Galactic black hole, possibly enhancing its accretion activity. No broad consensus has yet been reached concerning their nature: the G objects show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects. Here we report observations of four additional G objects, all lying within 0.04 parsecs of the black hole, and forming a class that is probably unique to this environment. The widely varying orbits derived for the six G objects demonstrate that they were commonly but separately formed.We used near-infrared (NIR) spectro-imaging data obtained over the past 13 years 11 at the W. M. Keck Observatory with the OSIRIS integral field spectrometer 12 , coupled with laser guide star adaptive optics wave front corrections 13 . OSIRIS data-cubes have two spatial dimensions -about 3 arcsec × 2 arcsec surrounding Sgr A* with a plate-scale of 35 mas-and one wavelength dimension -covering the Kn3 band, 2.121-2.229 µm, with a spectral resolution of R ≈ 3,800. We selected 24 datacubes based on image-quality and signal-to-noise ratio; see Methods section 'Observations'. These cubes were processed through the OSIRIS pipeline 14 . We also removed the stellar continua to isolate emission features associated with interstellar gas (Methods section 'Continuum subtraction'). The reduced data-cubes were analysed with a 3D visualization tool, OsrsVol 15 , that simultaneously displays all dimensions of the data-cube. This helps disentangle the many features of this crowded region, which are often superimposed in the spatial dimension but are separable in the wavelength dimension (Fig. 1).Analysing the data with OsrsVol as well as conventional 2D and 1D tools, we identify four new compact objects in Brackett-γ line emission (Brγ; 2.1661 µm rest wavelength) that consistently appear in the data across the observed timeline. In addition to Brγ, all four objects show two [Fe III] emission lines (at 2.1457 µm and 2.2184 µm; ref. 16 ).

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“…Considering the report of a drag force for the DSO/G2 by Gillessen et al (2019), it would be interesting to investigate the effect of the background subtraction.…”

Section: Nir Sourcesmentioning

confidence: 99%

Monitoring dusty sources in the vicinity of Sagittarius A*

Peißker

Hosseini

Eckart

et al. 2020

A&A

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Context. We trace several dusty infrared sources on their orbits around Sgr A* with SINFONI and NACO mounted at the VLT/Chile. These sources show near-infrared excess and Doppler-shifted line emission. We investigate these sources in order to clarify their nature and compare their relationship to other observed NIR objects close to Sgr A*. Aims. By using SINFONI, we are able to determine the spectroscopic properties of the investigated dusty infrared sources. Furthermore, we extract spatial and velocity information of these objects. We are able to identify X7, X7.1, X8, G1, DSO/G2, D2, D23, D3, D3.1, D5, and D9 in the Doppler-shifted line maps of the SINFONI H+K data. From our K-and L -band NACO data, we derive the related magnitudes of the brightest sources located west of Sgr A*. Methods. For determining the line of sight velocity information and to investigate single emission lines, we use the near-infrared integral field spectrograph SINFONI data-sets between 2005 and 2015. For the kinematic analysis, we use NACO data-sets between 2002 and 2018. This study is done in the H, K s , and L band. From the 3D SINFONI data-cubes, we extract line-maps in order to derive positional information of the sources. In the NACO images, we identify the dusty counterpart of the objects. If possible, we determine Keplerian orbits and apply a photometric analysis.Results. The spectrum of the investigated objects show a Doppler-shifted Brγ and HeI line emission. For some objects west of Sgr A*, we find additionally [Fe III] line emission that can be clearly distinguished from the background. A one-component blackbody model fits the extracted near-infrared flux for the majority of the investigated objects, with the characteristic dust temperature of 500 K. The photometric derived H-and K S -band magnitudes are between mag H > 22.5 and mag K = 18.1 +0.3 −0.8 for the dusty sources. For the H-band magnitudes we can provide an upper limit. For the bright dusty sources D2, D23, and D3, the Keplerian orbits are elliptical with a semi-major axis of a D2 = (749 ± 13) mas, a D23 = (879 ± 13), and a D3 = (880 ± 13) mas. For the DSO/G2, a single-temperature and a two-component blackbody model is fitted to the H-, K-, L -, and M-band data, while the two-component model that consists of a star and an envelope fits its SED better than an originally proposed single-temperature dusty cloud. Conclusions. The spectroscopic analysis indicates, that the investigated objects could be dust embedded pre-main-sequence stars. The Doppler-shifted [Fe III] line can be spectroscopically identified in several sources that are located between 17:45:40.05 and 17:45:42.00 in DEC. However, the sources with a DEC less than 17:45:40.05 show no [Fe III] emission. Therefore, these two groups show different spectroscopic features that could be explained by the interaction with a non-spherical outflow that originates at the position of Sgr A*. Followed by this, the hot bubble around Sgr A* consists out of isolated sources with [Fe III] line emission that can partially ...

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Detection of a Drag Force in G2's Orbit: Measuring the Density of the Accretion Flow onto Sgr A* at 1000 Schwarzschild Radii

Cited by 68 publications

References 69 publications

The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

A population of dust-enshrouded objects orbiting the Galactic black hole

Monitoring dusty sources in the vicinity of Sagittarius A*

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