Speaker
Description
We report the discovery of a candidate binary black hole system at redshift z~7.46, identified through high resolution spectroscopy of the Mg II λ2796,2803 doublet. The spectrum reveals a composite Mg II emission profile with two resolved doublets at closely spaced redshifts, z=7.454 and z=7.463. The intrinsically stronger Mg II λ2796 line shows suppression toward a near 1:1 flux ratio, consistent with absorption in optically thick gas typical of broad line regions (BLRs). Both doublets persist across multiple epochs, and their correlated short timescale variability with the continuum independently supports a BLR origin rather than association with the more extended narrow line region. The secondary doublet, displaced by ∼330 km s⁻¹ at z=7.463 together with the primary doublet at z=7.454, indicates a bound binary black hole system with two distinct BLRs. The velocity offset and dual BLR signatures align with hydrodynamical simulations of circumbinary accretion, in which each black hole sustains a mini disk and surrounding BLR. These observations provide evidence for the first binary black hole system identified in the early universe, offering new constraints on black hole growth and merger dynamics at cosmic dawn.
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