The Post-periapsis Evolution of Galactic Center Source G1: The Second Case of a Resolved Tidal Interaction with a Supermassive Black Hole

Abstract

We present new adaptive optics (AO) imaging and spectroscopic measurements of Galactic center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially resolved object interacting with a supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) and are comparatively close to the black hole (a min ∼200-300 au) on very eccentric orbits (e G1 ∼0.99; e G2 ∼0.96). While G2 has been tracked before and during periapsis passage (T 0 ∼2014.2), G1 has been followed since soon after emerging from periapsis (T 0 ∼2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1ʼs orbital trajectory appears to be in the same plane as that of G2 but with a significantly different argument of periapsis (Δω=21°±4°). This suggests that G1 is an independent object and not part of a gas stream containing G2, as has been proposed. Furthermore, we show for the first time that (1) G1 is extended in the epochs closest to periapsis along the direction of orbital motion, and (2) it becomes significantly smaller over time (450 au in 2004 to less than 170 au in 2009). Based on these observations, G1 appears to be the second example of an object tidally interacting with an SMBH. G1ʼs existence 14 yr after periapsis, along with its compactness in epochs further from the time of periapsis, suggest that this source is stellar in nature.

Investigating the Binarity of S0-2: Implications for Its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole

“…Two general classifications of mechanisms are considered for the S-stars: (1) binary star systems scattered from outside the region and then tidally disrupted, leaving behind one component of the original binary while the other was ejected as a hypervelocity star (Hills 1988;Perets et al 2007); and (2) S-stars formed in the clockwise disk and then migrated to the central arcsecond around the SMBH (Levin 2007;Löckmann et al 2008;Merritt et al 2009). Previous works have also investigated how these S-stars relate to the clockwise disk, Wolf-Rayet stars, G2-like sources, and evolved giants in the region ; Bartko et al 2009;Do et al 2009Do et al , 2013Lu et al 2009;Phifer et al 2013;Chen & Amaro-Seoane 2014;Madigan et al 2014;Witzel et al 2014Witzel et al , 2017.…”

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

“…For each source, neighbouring Lʹ sources were subtracted out using the flux values identified with StarFinder. Kʹ-identified sources that were not associated with the Lʹ sources based on proper motions were also subtracted from the analysis image assuming that they had the same magnitude and colour profiles as our flux calibration sources (S0-2, S0-12, S1-20 and S1-1 9,17 ). The images were then background-subtracted and Lucy-Richardson deconvolved using the background map and model PSF generated from StarFinder.…”

“…Several models (Methods section 'G-object formation scenarios') 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 or that generates a mass-loss envelope 26 , or the merger of a binary system 8,9,24,27 .…”

Confusing Binaries: The Role of Stellar Binaries in Biasing Disk Properties in the Galactic Center

“…For example, binaries are invoked to explain some long-standing observational puzzles, such as hypervelocity stars, the young stars in the S-cluster, the dark cusp, etc., (e.g., Hills 1988;Yu & Tremaine 2003;Antonini et al 2010;O'Leary et al 2009;Perets et al 2009;Alexander & Hopman 2009;Antonini & Perets 2012;Phifer et al 2013;Prodan et al 2015;Witzel et al 2014Witzel et al , 2017Stephan et al 2016). Furthermore, it has been suggested that compact object binaries in the GC are a potential source of gravitational wave emission (e.g., O'Leary et al 2009;Antonini & Perets 2012;Prodan et al 2015;Hoang et al 2017).…”

“…In such a system, gravitational perturbations from the SMBH can induce large eccentricities on the binary orbit, which can cause the binary members to merge (see for review of the dynamics Naoz 2016). This coalescence may form a new star that can look like the G2 and G1 objects (Phifer et al 2013;Prodan et al 2015;Witzel et al 2014Witzel et al , 2017Stephan et al 2016), which may eventually become blue stragglers (e.g., Naoz & Fabrycky 2014).…”