{
  "id": "1801.05780",
  "version": "v1",
  "published": "2018-01-17T18:10:03.000Z",
  "updated": "2018-01-17T18:10:03.000Z",
  "title": "A New Type of Extreme-mass-ratio Inspirals Produced by Tidal Capture of Binary Black Holes",
  "authors": [
    "Xian Chen",
    "Wen-Biao Han"
  ],
  "comment": "5 pages, 2 figures",
  "categories": [
    "astro-ph.HE",
    "gr-qc"
  ],
  "abstract": "Extreme-mass-ratio inspiral (EMRI) is an important gravitational-wave (GW) source and it normally consists of one stellar-mass black hole (BH) whirling closely around a supermassive black hole (SMBH). In this Letter, we demonstrate that the small body, in fact, could be a BH binary (BHB). Our work is motived by previous numerical scatting experiments which show that SMBHs can tidally capture BHBs to bound orbits. Here we investigate the subsequent long-term evolution. We find that only those BHBs with a semi-major axis of $a\\lesssim5\\times10^{-3}$ AU can be captured to tightly-bound orbits such that they will successfully inspiral towards the central SMBHs without being scattered away by stellar relaxation processes. We estimate that these binary-EMRIs (b-EMRIs) could constitute at most a few percent of the EMRI population. Moreover, we show that when the eccentricity of a b-EMRI drops to about $0.85$, the two stellar BHs will quickly merge due to the tidal perturbation by the SMBH. The high-frequency ($\\sim10^2$ Hz) GWs generated during the coalescence coincide with the low-frequency ($\\sim10^{-3}$ Hz) waves from the b-EMRI, making this system an ideal target for future multi-band GW observations.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-01-17T18:10:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "binary black holes",
      "extreme-mass-ratio inspiral",
      "tidal capture",
      "subsequent long-term evolution",
      "stellar-mass black hole"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 5,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}