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@ARTICLE{Ryu:617689,
      author       = {Ryu, Taeho and Seoane, Pau Amaro and Taylor, Andrew and
                      Ohlmann, Sebastian T.},
      title        = {{C}ollisions of red giants in galactic nuclei},
      journal      = {Monthly notices of the Royal Astronomical Society},
      volume       = {528},
      number       = {4},
      issn         = {0035-8711},
      address      = {Oxford},
      publisher    = {Oxford Univ. Press},
      reportid     = {PUBDB-2024-06980, arXiv:2307.07338},
      pages        = {6193-6209},
      year         = {2024},
      note         = {16 pages, 14 figures, 2 tables, accepted for publication in
                      MNRAS, comments welcome, movies here:
                      $https://www.youtube.com/playlist?list=PLxLK3qI02cQd9lyIo6DIqm1tQnx_-G3Ut$},
      abstract     = {In stellar-dense environments, stars can collide with each
                      other. For collisions close to a supermassive black hole
                      (SMBH), the collisional kinetic energy can be so large that
                      the colliding stars can be destroyed, potentially releasing
                      an amount of energy comparable to that of a supernova. These
                      black hole-driven disruptive collisions have been examined
                      mostly analytically, with the non-linear hydrodynamical
                      effects being left largely unstudied. Using the moving-mesh
                      hydrodynamics code arepo, we investigate high-velocity
                      $(>10^3$ km $s^−1)$ collisions between 1 $M_⊙$ giants
                      with varying radii, impact parameters, and initial
                      approaching velocities, and estimate their observables. Very
                      strong shocks across the collision surface efficiently
                      convert |${\gtrsim} 10~{{\ \rm per\ cent}}$| of the initial
                      kinetic energy into radiation energy. The outcome is a gas
                      cloud expanding supersonically, homologously, and
                      quasi-spherically, generating a flare with a peak luminosity
                      ≃10^41–10^44 erg s^−1 in the extreme ultraviolet band
                      (≃10 eV). The luminosity decreases approximately following
                      a power law of t^−0.7 initially, then t^−0.4 after t ≃
                      10 d at which point it would be bright in the optical band
                      (≲1eV). Subsequent, and possibly even brighter, emission
                      would be generated due to the accretion of the gas cloud on
                      to the nearby SMBH, possibly lasting up to multiyear
                      time-scales. This inevitable BH–collision product
                      interaction can contribute to the growth of BHs at all mass
                      scales, in particular, seed BHs at high redshifts.
                      Furthermore, the proximity of the events to the central BH
                      makes them a potential tool for probing the existence of
                      dormant BHs, even very massive ones which cannot be probed
                      by tidal disruption events.},
      keywords     = {hydrodynamics (autogen) / stars: kinematics and dynamics
                      (autogen) / Galaxy: nucleus (autogen) / quasars:
                      supermassive black holes (autogen) / Transients (autogen)},
      cin          = {$Z_THAT$},
      ddc          = {520},
      cid          = {$I:(DE-H253)Z_THAT-20210408$},
      pnm          = {613 - Matter and Radiation from the Universe (POF4-613) /
                      DFG project G:(GEPRIS)440719683 -
                      Hochleistungscompute-Cluster (440719683)},
      pid          = {G:(DE-HGF)POF4-613 / G:(GEPRIS)440719683},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)16},
      eprint       = {2307.07338},
      howpublished = {arXiv:2307.07338},
      archivePrefix = {arXiv},
      SLACcitation = {$\%\%CITATION$ = $arXiv:2307.07338;\%\%$},
      UT           = {WOS:001165257000007},
      doi          = {10.1093/mnras/stae396},
      url          = {https://bib-pubdb1.desy.de/record/617689},
}