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1. The Eccentric Nature of Eccentric Tidal Disruption Events

   https://doi.org/10.3847/1538-4357/ac32be  

   Cufari, M.; Coughlin, Eric R.; Nixon, C. J. (January 2022, The Astrophysical Journal)

   Abstract Upon entering the tidal sphere of a supermassive black hole, a star is ripped apart by tides and transformed into a stream of debris. The ultimate fate of that debris, and the properties of the bright flare that is produced and observed, depends on a number of parameters, including the energy of the center of mass of the original star. Here we present the results of a set of smoothed particle hydrodynamics simulations in which a 1 M ⊙ , γ = 5/3 polytrope is disrupted by a 10 6 M ⊙ supermassive black hole. Each simulation has a pericenter distance of r p = r t (i.e., β ≡ r t / r p = 1 with r t the tidal radius), and we vary the eccentricity e of the stellar orbit from e = 0.8 up to e = 1.20 and study the nature of the fallback of debris onto the black hole and the long-term fate of the unbound material. For simulations with eccentricities e ≲ 0.98, the fallback curve has a distinct, three-peak structure that is induced by self-gravity. For simulations with eccentricities e ≳ 1.06, the core of the disrupted star reforms following its initial disruption. Our results have implications for, e.g., tidal disruption events produced by supermassive black hole binaries. 

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2. Magnetorotational Instability in Eccentric Disks

   https://doi.org/10.3847/1538-4357/aab15c  

   Chan, Chi-Ho; Krolik, Julian H.; Piran, Tsvi (March 2018, The Astrophysical Journal)
3. Analytic waveforms for eccentric gravitational wave bursts

   https://doi.org/10.1088/1361-6382/ab745f  

   Loutrel, Nicholas (April 2020, Classical and Quantum Gravity)
4. The eccentric behavior of inspiralling compact binaries

   https://doi.org/10.1088/1361-6382/aaf2a9  

   Loutrel, Nicholas; Liebersbach, Samuel; Yunes, Nicolás; Cornish, Neil (January 2019, Classical and Quantum Gravity)
5. Spikey: Self-Lensing Flares from Eccentric SMBH Binaries

   https://doi.org/10.1093/mnras/staa1312  

   Hu, Betty X; D’Orazio, Daniel J; Haiman, Zoltán; Smith, Krista Lynne; Snios, Bradford; Charisi, Maria; Stefano, Rosanne Di (May 2020, Monthly Notices of the Royal Astronomical Society)

   Abstract We examine the light curves of two quasars, motivated by recent suggestions that a supermassive black hole binary (SMBHB) can exhibit sharp lensing spikes. We model the variability of each light curve as due to a combination of two relativistic effects: the orbital relativistic Doppler boost and gravitational binary self-lensing. In order to model each system we extend previous Doppler plus self-lensing models to include eccentricity. The first quasar is identified in optical data as a binary candidate with a 20-yr period (Ark 120), and shows a prominent spike. For this source, we rule out the lensing hypothesis and disfavor the Doppler-boost hypothesis due to discrepancies in the measured vs. recovered values of the binary mass and optical spectral slope. The second source, which we nickname Spikey, is the rare case of an active galactic nucleus (AGN) identified in Kepler’s high-quality, high-cadence photometric data. For this source, we find a model, consisting of a combination of Doppler modulation and a narrow symmetric lensing spike, consistent with an eccentric SMBHB with mass Mtot = 3 × 107M⊙, rest-frame orbital period T = 418 days, eccentricity e = 0.5, and seen at an inclination 8○ from edge-on. This interpretation can be tested by monitoring Spikey for periodic behavior and recurring flares in the next few years. In preparation for such monitoring we present the first X-ray observations of this object taken by the Neil Gehrels Swift observatory. 

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