A recent study led by Filippo Mannucci (INAF/Osservatorio Astrofisico di Arcetri) reported observations by the Large Binocular Telescope and Hubble Space Telescope confirming candidates for multiple supermassive black holes at small angular separation.

These objects, identified as active galactic nuclei based on the radiative signature of matter accreting onto the central compact object, were selected as potential multiple systems based on measurements from the Gaia satellite suggesting the presence of more than one peak in the light distribution seen on the sky. The LBT and HST delivered high angular resolution images allowing the sources to be seen as distinct pairs or multiple sources for the first time.

Dual supermassive black holes are of interest as candidates for merging systems that will ultimately spiral together while releasing huge amounts of energy in gravitational waves. Models tracing the formation and development of galaxies, along with their central black holes, predict the occurrence of such mergers as they evolve over cosmic time.

Multiple systems can alternatively represent images of a single active galactic nucleus, produced through the bending of light by a massive object at intermediate distance, through a process known as gravitational lensing. Gravitational lenses provide a novel means for tracing the distribution of dark matter and measuring cosmological parameters.

The LBT measurements made use of the LUCI1 infrared camera assisted by the SOUL implementation of natural guide-star, single conjugate adaptive optics.

The results are published in Mannucci et al. (2022),Nature Astronomy, 6, 1185