A young massive stellar population around the intermediate-mass black hole ESO 243-49 HLX-1

S. A. Farrell, M. Servillat, Janine Pforr, Thomas J. Maccarone, C. Knigge, O. Godet, Claudia Maraston, N. A. Webb, D. Barret, A. J. Gosling, R. Belmont, K. Wiersema

Research output: Contribution to journalArticlepeer-review


We present Hubble Space Telescope and simultaneous Swift X-ray Telescope observations of the strongest candidate intermediate-mass black hole (IMBH) ESO 243-49 HLX-1. Fitting the spectral energy distribution from X-ray to near-infrared wavelengths showed that the broadband spectrum is not consistent with simple and irradiated disk models, but is well described by a model comprised of an irradiated accretion disk plus a ~106 M stellar population. The age of the population cannot be uniquely constrained, with both young and old stellar populations allowed. However, the old solution requires excessive disk reprocessing and an extremely small disk, so we favor the young solution (~13 Myr). In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy suggest that a gas-rich minor merger may have taken place less than ~200 Myr ago. Such a merger event would explain the presence of the IMBH and the young stellar population.
Original languageEnglish
Article numberL13
Pages (from-to)L13
JournalAstrophysical Journal Letters
Issue number1
Early online date15 Feb 2012
Publication statusPublished - 1 Mar 2012


  • accretion, accretion disks
  • galaxies: interactions
  • galaxies: star clusters: general
  • globular clusters: general
  • X-rays: binaries
  • X-rays: individual (ESO 243-49 HLX-1)


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