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We present analysis of Chandra X-ray observations of seven quasars that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on the apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs, including harder or softer X-ray spectra, ripple-like profiles in the Fe K-α line, and distinct peaks in the spectrum due to the separation of the accretion disk into a circumbinary disk and mini disks around each SMBH. We obtained Chandra observations to test these models and assess whether these quasars could contain binary SMBHs. We instead find that the quasar spectra are all well fit by simple absorbed power-law models, with the rest-frame 2–10 keV photon indices, Γ, and the X-ray-to-optical power slopes, α_(OX), indistinguishable from those of the larger quasar population. This may indicate that these seven quasars are not truly subparsec binary SMBH systems, or it may simply reflect that our sample size was too small to robustly detect any differences. Alternatively, the X-ray spectral changes might only be evident at energies higher than probed by Chandra. Given the available models and current data, no firm conclusions are drawn. These observations will help motivate and direct further work on theoretical models of binary SMBH systems, such as modeling systems with thinner accretion disks and larger binary separations.

Among the growing list of confirmed exoplanets, the number of planets identified in dense star clusters remains sparse. Previous analyses have suggested this may be due in part to dynamical interactions that unbind large fractions of planets from their host stars, limiting the survival of planetary systems in clusters. Thus, alternative detection strategies may be necessary to study planets in clusters that may no longer be bound to a host star. Here, we use the cluster Monte Carlo code CMC to explore the evolution of planetary systems in dense star clusters. Depending on a number of initial conditions, we show that $10-50\%$ of primordial planetary systems are broken through dynamical encounters over a cluster's full lifetime, populating clusters with "free-floating" planets. Furthermore, a large number ($30-80\%$) of planets are ejected from their host cluster through strong dynamical encounters and/or tidal loss. Additionally, we show that planets naturally mix with stellar-mass black holes (BHs) in the central regions of their host cluster. As a consequence, up to a few hundreds of planets will be tidally disrupted through close passages of BHs. We show these BH-planet tidal disruption events (TDEs) occur in clusters at a rate of up to $10^{-5}\,\rm{yr}^{-1}$ in a Milky Way-type galaxy. We predict BH-planet TDEs should be detected by upcoming transient surveys such as LSST at a rate of roughly a few events per year. The observed rate of BH-planet TDEs would place new constraints upon the formation and survival of both planetary systems and BHs in dense star clusters. Additionally, depending on various assumptions including the initial number of planets and their orbital properties, we predict that typical globular clusters may contain a few dynamically-formed NS-planet systems at present as well as up to roughly 100 dynamically-formed WD-planet systems., 18 pages, 8 figures. Submitted to ApJ. Comments welcome