The Emergence of Little Red Dots from Binary Massive Black Holes
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| Format: | Preprint |
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2025
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| _version_ | 1866908996158357504 |
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| author | Inayoshi, Kohei Shangguan, Jinyi Chen, Xian Ho, Luis C. Haiman, Zoltan |
| author_facet | Inayoshi, Kohei Shangguan, Jinyi Chen, Xian Ho, Luis C. Haiman, Zoltan |
| contents | Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGN) with a distinctive v-shape spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of $z\sim6-8$ and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, where each black hole is surrounded by a mini-disk and embedded in a larger circum-binary disk. With a binary separation of $\lesssim 10^3$ Schwarzschild radii, the Wien tail of a $T\simeq 5000~{\rm K}$ blackbody spectrum at the inner edge of the circum-binary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circum-binary disk and mini-disks, setting the turnover wavelength of the v-shaped spectrum around the Balmer limit. This scenario naturally reproduces LRD spectra requiring only modest dust attenuation ($A_V\lesssim 1$ mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Soltan argument. This model predicts a distinct spectral evolution as the binary orbit decays through binary-disk interactions and gravitational waves (GWs), linking early-stage "proto-LRD" binaries to the broader AGN population and late-stage "LRD-descendants" to coalescing binaries detectable in GW experiments. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2505_05322 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Emergence of Little Red Dots from Binary Massive Black Holes Inayoshi, Kohei Shangguan, Jinyi Chen, Xian Ho, Luis C. Haiman, Zoltan High Energy Astrophysical Phenomena Astrophysics of Galaxies Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGN) with a distinctive v-shape spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of $z\sim6-8$ and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, where each black hole is surrounded by a mini-disk and embedded in a larger circum-binary disk. With a binary separation of $\lesssim 10^3$ Schwarzschild radii, the Wien tail of a $T\simeq 5000~{\rm K}$ blackbody spectrum at the inner edge of the circum-binary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circum-binary disk and mini-disks, setting the turnover wavelength of the v-shaped spectrum around the Balmer limit. This scenario naturally reproduces LRD spectra requiring only modest dust attenuation ($A_V\lesssim 1$ mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Soltan argument. This model predicts a distinct spectral evolution as the binary orbit decays through binary-disk interactions and gravitational waves (GWs), linking early-stage "proto-LRD" binaries to the broader AGN population and late-stage "LRD-descendants" to coalescing binaries detectable in GW experiments. |
| title | The Emergence of Little Red Dots from Binary Massive Black Holes |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2505.05322 |