New Observations of the Gas Cloud G2 in the Galactic Center

Gillessen, S.; Genzel, R.; Fritz, Tobias; Eisenhauer, F.; Pfuhl, O.; Ott, Thomas; Cuadra, Jorge; Schartmann, M.; Burkert, Andreas

doi:10.1088/0004-637x/763/2/78

Cited by 106 publications

(228 citation statements)

References 33 publications

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“…This agrees with observations reporting that G2 is composed of a compact head and a more widespread tail (Gillessen et al 2013b;Pfuhl et al 2015). The two components are on approximately the same orbit and are connected by a faint bridge in positionvelocity diagrams, in Gillessen et al (2013a) and lasted over one year,while G2 has been stretched substantially along its orbit by tidal shearing caused by the gravitational potential of Sgr A* Article published by EDP Sciences L16, page 1 of 4 (Pfuhl et al 2015). Test particle simulations have provided a good explanation for the dynamics of G2; the results showed that hydrodynamic effects have not been significant (e.g., Pfuhl et al 2015; see also Schartmann et al 2012).…”

Section: Introductionsupporting

confidence: 92%

No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

Park

Trippe

Krichbaum

et al. 2015

A&A

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The gas cloud G2 that falls toward Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is assumed to provide valuable information on the physics of accretion flows and the environment of the black hole. We observed Sgr A* with four European stations of the Global Millimeter Very Long Baseline Interferometry Array (GMVA) at 86 GHz on 1 October 2013 when parts of G2 had already passed the pericenter. We searched for a possible transient asymmetric structure -such as jets or winds from hot accretion flows -around Sgr A* that might be caused by accretion of material from G2. The interferometric closure phases remained zero within errors during the observation time. We therefore conclude that Sgr A* did not show significant asymmetric (in the observer frame) outflows in late 2013. Using simulations, we constrain the size of the outflows that we could have missed to ≈2.5 mas along the major axis and ≈0.4 mas along the minor axis of the beam, corresponding to approximately 232 and 35 Schwarzschild radii, respectively; we thus probe spatial scales on which the jets of radio galaxies are thought to convert magnetic into kinetic energy. Because probably less than 0.2 Jy of the flux from Sgr A* can be attributed to accretion from G2, the effective accretion rate is ηṀ 1.5 × 10 9 kg s −1 ≈ 7.7 × 10 −9 M ⊕ yr −1 for material from G2. Exploiting the relation of kinetic jet power to accretion power of radio galaxies shows that the rate of accretion of matter that is finally deposited in jets is limited toṀ 10 17 kg s −1 ≈ 0.5 M ⊕ yr −1 . Accordingly, G2 appears to be mostly stable against loss of angular momentum and subsequent (partial) accretion at least on timescales 1 yr.

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Section: Introductionsupporting

confidence: 92%

No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

Park

Trippe

Krichbaum

et al. 2015

A&A

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“…The tidal disruption of this cloud is being monitored by different groups (e.g., Eckart et al 2013;Gillessen et al 2013;Phifer et al 2013) and provides a unique opportunity to test accretion physics, due to both its proximity and the timescale on which it happens. Gillessen et al (2012) estimated the mass of G2 to be ∼ 3 M⊕ from its line emission.…”

Section: Introductionmentioning

confidence: 99%

Clump formation through colliding stellar winds in the Galactic Centre

Calderón

Ballone

Cuadra

et al. 2015

Mon. Not. R. Astron. Soc.

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The gas cloud G2 is currently being tidally disrupted by the Galactic Centre super-massive black hole, Sgr A*. The region around the black hole is populated by ∼ 30 Wolf-Rayet stars, which produce strong outflows. We explore the possibility that gas clumps, such as G2, originate from the collision of stellar winds via the non-linear thin shell instability. Following an analytical approach, we study the thermal evolution of slabs formed in the symmetric collision of winds, evaluating whether instabilities occur, and estimating possible clump masses. We find that the collision of relatively slow ( < ∼ 750 km s −1 ) and strong (∼ 10 −5 M ⊙ yr −1 ) stellar winds from stars at short separations (< 10 mpc) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their known orbits are not common in the Galactic Centre, making this process a possible but unlikely origin for G2. We also discuss clump formation in close binaries such as IRS 16SW and in asymmetric encounters as promising alternatives that deserve further numerical study.

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“…As a specific example, we used the L -band based nominal orbital elements of G2/DSO (Gillessen et al 2013a). The resulting evolution is plotted in Fig.…”

Section: Role Of Central Starmentioning

confidence: 99%

“…Gillessen et al (2012Gillessen et al ( , 2013a studied the evolution of such a cloud of particles in the field of the Sgr A* SMBH. We revisited their simulations by including the interaction with different prescriptions for the ambient wind.…”

Section: Role Of Central Starmentioning

confidence: 99%

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Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei

Karas

Eckart

2014

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Context. Supermassive black holes reside in cores of galaxies, where they are often surrounded by a nuclear cluster and a clumpy torus of gas and dust. Mutual interactions can set some stars on a plunging trajectory towards the black hole. Aims. We model the pericentre passage of a dust-enshrouded star during which the dusty envelope becomes stretched by tidal forces and is affected by the interaction with the surrounding medium. In particular, we explore under which conditions these encounters can lead to periods of enhanced accretion activity. Methods. We discuss different scenarios for such a dusty source. To this end, we employed a modification of the Swift integration package. Elements of the cloud were modelled as numerical particles that represent the dust component that interacts with the optically thin gaseous environment. Results. We determine the fraction of the total mass of the dust component that is diverted from the original path during the passages through the pericentre at 10 3 Schwarzschild radii and find that the main part of the dust ( 90% of its mass) is significantly affected upon the first crossing. The fraction of mass captured at the second passage generally decreases to very low values. Conclusions. As an example, we show predictions for the dusty source evolution assuming the current orbital parameters of the G2 cloud (also known as Dusty S-Cluster Object, DSO) in our Galactic centre. Encounter of a core-less cloud with a supermassive black hole is, most likely, a non-repeating event: the cloud is destroyed. However, in the case of a dust-enshrouded star, part of the envelope survives the pericentre passage. We discuss an offset of 0.3 arcsec between the centre of mass of the diverted part and the star along the eccentric orbit. Finally, we examine an interesting possibility of a binary star embedded within a common wind envelope that becomes dispersed at the pericentre passage.

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New Observations of the Gas Cloud G2 in the Galactic Center

Cited by 106 publications

References 33 publications

No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2

Clump formation through colliding stellar winds in the Galactic Centre

Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei

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