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We present new absolute proper-motion measurements for the Arches and Quintuplet clusters, two young massive star clusters near the Galactic center. Using multiepoch HST observations, we construct proper-motion catalogs for the Arches (∼35,000 stars) and Quintuplet (∼40,000 stars) fields in ICRF coordinates established using stars in common with the Gaia EDR3 catalog. The bulk proper motions of the clusters are measured to be (μ_α*,μ_δ) = (−0.80 ± 0.032, −1.89 ± 0.021) mas yr⁻¹for the Arches and (μ_α*,μ_δ) = (−0.96 ± 0.032, −2.29 ± 0.023) mas yr⁻¹for the Quintuplet, achieving ≳5× higher precision than past measurements. We place the first constraints on the properties of the cluster orbits that incorporate the uncertainty in their current line-of-sight distances. The clusters will not approach closer than ∼25 pc to Sgr A*, making it unlikely that they will inspiral into the nuclear star cluster within their lifetime. Further, the cluster orbits are not consistent with being circular; the average value ofr_apo/r_periis ∼1.9 (equivalent to an eccentricity of ∼0.31) for both clusters. Lastly, we find that the clusters do not share a common orbit, challenging one proposed formation scenario in which the clusters formed from molecular clouds on the open stream orbit derived by Kruijssen et al. Meanwhile, our constraints on the birth location and velocity of the clusters offer mild support for a scenario in which the clusters formed via collisions between gas clouds on thex₁andx₂bar orbit families.

 

Type Ia supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving (V_peculiar> 1000 km s⁻¹), overluminous (L> 0.1L_⊙) white dwarf. Recently, three objects that appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high-precision astrometric proper-motion survey of the interior stellar population of the remnant. We rule out the existence of a high-proper-motion object consistent with our tested realization of the D6 scenario (V_transverse> 600 km s⁻¹withm_r< 21 corresponding to an intrinsic luminosity ofL> 0.0176L_⊙). We conclude that such a star does not exist within the remnant or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system almost parallel to the line of sight.

 

ABSTRACT The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s−1, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M⊙ and was captured into a highly eccentric orbit with pericentre distance in the range of 1–10 au and semimajor axis about 103 au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about $3\rm \, au$. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below $3\rm \, au$ and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10–100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically $K_{\rm s}\lesssim 18.5\,$ mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*. 

Abstract This supplement provides supporting material for Lam et al. We briefly summarize past gravitational microlensing searches for black holes (BHs) and present details of the observations, analysis, and modeling of five BH candidates observed with both ground-based photometric microlensing surveys and Hubble Space Telescope astrometry and photometry. We present detailed results for four of the five candidates that show no or low probability for the lens to be a BH. In these cases, the lens masses are <2 M ⊙ , and two of the four are likely white dwarfs or neutron stars. We also present detailed methods for comparing the full sample of five candidates to theoretical expectations of the number of BHs in the Milky Way (∼10 8 ).