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  • Formation and Evolution of Compact Binaries Containing Intermediate-mass Black Holes in Dense Star Clusters
    We investigate the evolution of star clusters containing intermediate-mass black holes (IMBHs) of 300–5000 M⊙, focusing on the formation and evolution of IMBH–stellar-mass black hole (MBH ≲ 102M⊙) binaries. Dense stellar systems like globular clusters (GCs) or nuclear star clusters offer unique laboratories for studying the existence and impacts of IMBHs. IMBHs residing in GCs have been under speculation for decades, with their broad astrophysical implications for the cluster’s dynamical evolution, stellar population, and gravitational-wave (GW) signatures, among others. While existing GW observatories, such as the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO), target binaries with relatively modest mass ratios, q ≲ 10, future observatories, such as the Einstein Telescope (ET) and the Laser Interferometer Space Antenna (LISA), will detect intermediate-mass ratio inspirals (IMRIs) with q > 10. This work explores the potential for detecting IMRIs by adopting these upcoming telescopes. For our experiments, we perform multiple direct N-body simulations with IMBHs, utilizing Nbody6++GPU, after implementing the GW merger schemes for IMBHs. We then study the statistical properties of the resulting IMRIs, such as the event rates and orbital properties. Assuming that IMRIs with a signal-to-noise ratio > 8 are detectable, we derive the following detection rates for each observatory: ≲0.02 yr−1 for aLIGO, ∼101−355 yr−1 for ET, ∼186−200 yr−1 for LISA, ∼0.24−0.34 yr−1 for aSOGRO, and ∼3880−4890 yr−1 for DECIGO. Our result confirms the capability of detecting IMRIs with future GW telescopes.

  • 3D Magnetohydrodynamic Wave Propagation and Energy Transport in a Simulated Solar Vortex
    Magnetic flux tubes in the presence of background rotational flows are abundant throughout the solar atmosphere and may act as conduits for MHD waves to transport energy throughout the solar atmosphere. Here we investigate the contribution from MHD waves to the Poynting flux in a 3D numerical simulation of a realistic solar atmosphere, modeling a structure resembling a solar vortex tube, using the PLUTO code in the presence of different plasma flow configurations. These simulations feature a closed magnetic loop system where a rotational flow is imposed at one footpoint in addition to photospheric perturbations acting as a wave driver mimicking those of p-modes. We find that a variety of MHD waves exist within the vortex tube, including sausage, kink, and torsional Alfvén waves, owing to the photospheric wave driver and the nature of the rotational flow itself. We demonstrate how the visual interpretation of different MHD modes becomes nontrivial when a background rotational flow is present compared to a static flux tube. By conducting a simulation both with and without the rotational plasma flow, we demonstrate how the perturbed Poynting flux increases in the presence of the rotational flow as the waves transport increased magnetic energy. We attribute this increase to the dynamical pressure from the rotational flow increasing the plasma density at the tube boundary, which acts to trap the wave energy more effectively inside the vortex. Moreover, we demonstrate how the Poynting flux is always directed upward in weakly twisted magnetic flux tubes.

  • A Cometary Fluorescence Model for the ν 3 Vibrational Band of Cyanogen
    Cyanogen (C2N2) has been suspected for a long time to be present in comets and to contribute to the creation of the CN radical. So far no observations with ground-based facilities have managed to detect this species, but the Rosetta mission, thanks to in situ observations with the ROSINA mass spectrometer, detected this species in the coma of 67P/Churyumov–Gerasimenko. To investigate its presence from infrared spectra in other comets, we developed a fluorescence model for the ν3 fundamental band. From new laboratory high-resolution infrared spectra of cyanogen, we analyzed the region of the ν3 band of C2N2, centered around 4.63 μm (2158 cm−1). In addition to line positions and intensities, molecular parameters for the ground and excited vibrational state were obtained. These parameters allowed us to develop a fluorescence model for cyanogen. Line-by-line excitation rates of the ν3 band of cyanogen in cometary comae are presented. An upper limit of the abundance of cyanogen in a spectrum of comet C/2022 E3 (ZTF) is discussed.

  • Low Accretion Rates in Black Holes in Late-stage Merger Ultraluminous Infrared Galaxies
    We explore the accretion rates of supermassive black holes (SMBHs) in late-stage galaxy mergers by observing three ultraluminous infrared galaxies (ULIRGs), IRAS 14378-3651, IRAS 17208-0014 and IRAS 23365+3604, using the JWST/MIRI Medium Resolution Spectrometer and JWST/NIRSpec integral field unit. In all three cases, we fail to detect [Ne vi] λ7.65 μm, a robust active galactic nuclei (AGN) tracer lying in a low-opacity interstellar window, nor do we detect any other lines that might indicate AGNs. The only detected high-excitation emission line, [Mg iv] (λ4.488 μm), arises from shocks associated with supernovae. Our new, deep flux limits on AGN tracers in the near- and mid-infrared indicate that the nuclear obscuration of any purported AGNs in our sample is isotropic, i.e., the far-infrared luminosities of these galaxies are unlikely to be driven by escaping AGN power. This allows us to show that the Eddington ratios of their SMBHs are low. We then assemble an unbiased sample of 19 ULIRGs (from the IRAS Bright Galaxy Sample with L(TIR) ≥ 1012L⊙) in late-stage mergers and show that their dynamically measured black hole masses are consistent with the values from scaling from their stellar masses. On this basis, we show that the Eddington ratios of any AGNs in 15 of these galaxies are also very low, ≲10%. This indicates that any black holes are in a relatively quiescent state. That is, high levels of accretion are found in only a minority of late-merger-phase ULIRGs.

  • Two Events with Spectacular Moving Structures in a Failed Solar Filament Eruption
    We investigate the complex magnetic reconnection process between the filament and surrounding loops during the failed filament eruption that occurred in NOAA active region 13445 on 2023 September 24, using extreme-ultraviolet observations from the Solar Dynamics Observatory and high-resolution Hα imaging from the New Vacuum Solar Telescope. This failed filament eruption is associated with an M4.4 flare (SOL2023-09-24T03:28). At the early phase of the filament eruption, the filament displays a distinct clockwise rotational motion, suggesting an untwisting motion. During the flare precursor phase, the northwest slipping motion of the brightenings at the filament’s left footpoint, along with the brightening and continuous expansion of the nearby loops at the northwest, suggest the occurrence of a slipping magnetic reconnection between the filament and peripheral loops at the quasi-separatrix layer. After the slipping motion begins, significant brightenings of filament materials and multiple bright structures moving toward the two filament footpoints are observed during the two episodes of magnetic reconnection between the filament and the overlying loops, with the most prominent brightenings and the moving structures occurring during the main phase of the M4.4 flare. The observed untwisting motion of the filament and the twist reduction derived from the nonlinear force-free field extrapolation suggest that the magnetic reconnection between the filament and the peripheral and overlying loops plays a significant role in the failure of the filament eruption by greatly reducing its twist.