Constraining the Variability and Binary Fraction of Galactic Center Young Stars

Abstract

Abstract. We present constraints on the variability and binarity of young stars in the central 10 arcseconds (∼ 0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment's photometric uncertainties, at least 36% of our sample's known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence.Keywords. Galaxy: center, stars: early-type, (stars:) binaries: eclipsingIn this work, we better constrain the Milky Way Galactic Center (GC) binary fraction with much larger samples, improving upon previous studies limited to the brightest sources. Tighter binary fraction constraints are especially useful to understand the formation and dynamics of young stars in the nuclear star cluster near the central supermassive black hole: The fragmentation of an accretion disk around the black hole could have formed the young stars currently observed in the clockwise disk at the GC (Alexander et al. 2008). The binary fraction also constrains the binary disruption mechanism (Hills 1988) that could explain the origin of the observed young S-stars within ∼ 0.05 pc of the central supermassive black hole.We used laser guide-star adaptive optics high-resolution images of the GC obtained at the 10 m. W. M. Keck II telescope with the NIRC2 near-infrared facility imager through the K (λ 0 = 2.124 µm) bandpass. The images were centered near the position of Sgr A* and span 10 arcseconds (∼ 0.4 pc at R 0 ≈ 8.0 kpc), and were taken over 37 nights between July 2004 and May 2016 (observation setup used here is further detailed by Ghez et al. 2008 andYelda et al. 2014).Variable stars were identified as those displaying photometric fluctuations above that expected from 7σ noise fluctuations. At least 36% of the 72 known early-type stars identified in all nights are variable.To identify eclipsing binaries, we conducted a periodic variability search on 124 spectroscopically confirmed or likely early-type stars (p(Early-Type) 0.5, from Do et al.1

Can supernova kicks trigger EMRIs in the Galactic Centre?

“…Our investigation suffers from a number of limitations. First of all, we neglect the possibility that stars exploding as SNe may be members of a binary system; this aspect is important, especially considering that the binary fraction in the CW disc probably lies in the range 30 − 85% (Pfuhl et al 2014;Gautam et al 2017; see also Hopman 2009 for comprehensive study about the survival of binaries near a SMBH). As a matter of fact, Lu & Naoz (2019) explore the dynamics of SN kicks in triple systems, the third body possibly being an SMBH.…”

Infalling Young Clusters in the Galactic Centre: implications for IMBHs and young stellar populations

“…This mechanism produces S-stars with eccentricities lower than from the disruption of binaries originating from outside the disk. However, in order to thermalize the S-stars, ∼ 500 M in dark remnants are still required around SgrA* in order to match observations, consistent with Fokker-Planck models (Hopman & Alexander 2006 Gautam et al (2016) predict that the binary fraction must be greater than 32% at 90% confidence.…”

“…The inclusion of primordial binaries is interesting as the clockwise disk has three confirmed eclipsing binaries Martins et al 2006;Pfuhl et al 2014), with a total binary population estimated to be greater than 30% (Pfuhl et al 2014;Gautam et al 2016). Secondly, a popular formation scenario for the S-stars is from the tidal disruption of binaries by SgrA* via the Hills mechanism (Hills 1991(Hills , 1992, where one star is captured and the other is ejected as a hyper-velocity star.…”