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

Abstract

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.

Nature of the Galactic centre NIR-excess sources

“…In this paper, we further elaborate on a model of the DSO (see previous models presented in Zajaček et al 2014Zajaček et al , 2016 taking into account the new K s -band measurements and analysis as presented by Shahzamanian et al (2016). By comparing theoretical and numerical calculations with the NIR data, we can explain the peculiar characteristics of the DSO by using the model of a young embedded and accreting star surrounded by a nonspherical dusty envelope.…”

“…(i) core-less cloud/streamer (Gillessen et al 2012;Burkert et al 2012;Schartmann et al 2012;Pfuhl et al 2015;Schartmann et al 2015) Article (ii) a dust-enshrouded star (Murray-Clay & Loeb 2012;Eckart et al 2013;Scoville & Burkert 2013;Ballone et al 2013;Zajaček et al 2014;De Colle et al 2014;Valencia-S. et al 2015;Ballone et al 2016) (iii) binary/binary dynamics Prodan et al 2015;Witzel et al 2014) The scenarios (i), (ii), (iii), and a few more are summarized in Table 1 with corresponding references.…”

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

“…Recent observations have also shown that G2 survived its pericenter passage as a compact source, which might be a clue that G2 is a star enshrouded by gas and/or dust (Witzel et al 2014;Valencia et al 2015). This scenario was modeled analytically (Miralda-Escudé 2012; Scoville & Burkert 2013) and explored with the help of numerical simulations (Ballone et al 2013;De Colle et al 2014;Zajaček et al 2014).…”

The black hole at the Galactic Center: Observations and models

“…The authors predicted that the cloud should be disrupted near its pericenter d passage. However, subsequent observations showed that the object was not disrupted after the pericenter passage, therefore, it was concluded that it is a dust-enshrouded star [76,77,78] or a young star [79].…”