Direct imaging of sub-parsec binary SMBHs in the central galaxy of the NGC 5044 group

@misc{ubertosi2026direct,
  title = {{Direct imaging of sub-parsec binary SMBHs in the central galaxy of the NGC 5044 group}},
  author = {Francesco Ubertosi and Gerrit Schellenberger and Ewan O'Sullivan and Laurence P. David and William Forman and Simona Giacintucci and Christine Jones and Kamlesh Rajpurohit and Tiziana Venturi and Jan Vrtilek},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.22433},
  eprint = {2609.22433},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.22433},
}

TY  - UNPB
TI  - Direct imaging of sub-parsec binary SMBHs in the central galaxy of the NGC 5044 group
AU  - Francesco Ubertosi
AU  - Gerrit Schellenberger
AU  - Ewan O'Sullivan
AU  - Laurence P. David
AU  - William Forman
AU  - Simona Giacintucci
AU  - Christine Jones
AU  - Kamlesh Rajpurohit
AU  - Tiziana Venturi
AU  - Jan Vrtilek
PY  - 2026
DA  - 2026/09/18
PB  - arXiv
DO  - 10.48550/arxiv.2609.22433
UR  - https://arxiv.org/abs/2609.22433
AB  - Binary active galactic nuclei (AGN) consist of two supermassive black holes (SMBHs) hosted in a single galaxy that are simultaneously accreting gas. These systems are key to understanding hierarchical galaxy evolution and represent prime targets for low-frequency gravitational wave (GW) experiments. However, binary AGN remain extremely rare: only a handful are confirmed at separations of a few hundred parsecs, and just one pc-scale binary - in an elliptical galaxy at the center of a galaxy cluster - has been securely and visually identified. Direct imaging of sub-parsec binary AGN, the final stage before the GW regime, has so far been missing. Here we report on Very Long Baseline Array (VLBA) observations of NGC 5044, the central galaxy of the X-ray brightest galaxy group. This galaxy is known to exhibit pc-scale radio jets nearly orthogonal to two older AGN outbursts. The 4.9, 8.4, 15.2, and 23.6 GHz VLBA images reveal two compact, flat-spectrum, and variable radio cores separated by just 0.38 parsec at the heart of the galaxy, forming the tightest directly imaged binary AGN known by an order of magnitude. This discovery suggests that the older outbursts may have been powered by jets from the secondary core, without invoking any reorientation of the primary jet axis. More broadly, comparison with other systems points to massive, cluster-central elliptical galaxies being promising targets to search for binary SMBHs.
ER  -