First Detection of an Overmassive Black Hole Galaxy UHZ1: Evidence for Heavy Black Hole Seed Formation from Direct Collapse

Abstract

The recent Chandra-JWST discovery of a quasar in the z ≈ 10.1 galaxy UHZ1 reveals that accreting supermassive black holes were already in place 470 million years after the Big Bang. The Chandra X-ray source detected in UHZ1 is a Compton-thick quasar with a bolometric luminosity of L bol ∼ 5 × 1045 erg s−1, which corresponds to an estimated black hole (BH) mass of ∼4 × 107 M ⊙, assuming accretion at the Eddington rate. JWST NIRCAM and NIRSpec data yield a stellar mass estimate for UHZ1 comparable to its BH mass. These characteristics are in excellent agreement with prior theoretical predictions for a unique class of transient, high-redshift objects, overmassive black hole galaxies (OBGs) by Natarajan et al., that harbor a heavy initial black hole seed that likely formed from the direct collapse of the gas. Given the excellent agreement between the observed multiwavelength properties of UHZ1 and theoretical model template predictions, we suggest that UHZ1 is the first detected OBG candidate. Our assertion rests on multiple lines of concordant evidence between model predictions and the following observed properties of UHZ1: its X-ray detection and the estimated ratio of the X-ray flux to the IR flux, which is consistent with theoretical expectations for a heavy initial BH seed; its high measured redshift of z ≈ 10.1, as predicted for the transient OBG stage (9 < z < 12); the amplitude and shape of the detected JWST spectral energy distribution (SED) between 1 and 5 μm, which is in very good agreement with simulated template SEDs for OBGs; and the extended JWST morphology of UHZ1, which is suggestive of a recent merge and is also expected for the formation of transient OBGs. As the first OBG candidate, UHZ1 provides compelling evidence for the formation of heavy initial seeds from direct collapse in the early Universe.

Overmassive Black Holes at Cosmic Noon: Linking the Local and the High-redshift Universe

“…It is conceivable that these extremely bright sources are preferentially overmassive. It has been argued persuasively at least in the case of the z = 10.1 source UHZ1 that this system was likely seeded with a massive seed of 10 4 -10 5 M e causing it to be overmassive (Bogdán et al 2024;Natarajan et al 2024). So, heavy seeding coupled with feedback physics as noted by Pacucci & Loeb (2024) might be implicated in these extremely high-redshift sources.…”

“…Other possibilities include early super-Eddington growth (Volonteri & Rees 2005), stellar mergers in early nuclear stellar clusters (e.g., Portegies Zwart et al 1999;Devecchi & Volonteri 2009), rapid growth of light seeds via wind-fed accretion in early nuclear star clusters (Alexander & Natarajan 2014), and primordial BHs (e.g., Cappelluti et al 2022;Ziegler & Freese 2022). There is growing evidence that the recent detection of 10 6 -10 7 M e BHs at z > 8 favors the heavy seeding scenario, as lighter seeds would require periods of super-Eddington accretion (e.g., Pacucci & Loeb 2022;Bogdán et al 2024;Larson et al 2023;Maiolino et al 2024;Natarajan et al 2024).…”

The Redshift Evolution of the M •–M ⋆ Relation for JWST’s Supermassive Black Holes at z > 4

“…Second, it may inform us of the seeding mechanism that formed the central black hole in the first place. In fact, several studies have shown that a high ratio M • /M å may be indicative of the formation of a heavy seed (see, e.g., Agarwal et al 2013;Natarajan et al 2017;Visbal & Haiman 2018;Scoggins et al 2023;Natarajan et al 2024) at z > 20. The study of the properties of central SMBHs and their hosts at high-z, as well as the detection of extremely massive, and rare SMBHs at z > 10, will determine if heavy seed formation channels were active in the high-z Universe (Pacucci & Loeb 2022).…”

Detectability of Supermassive Dark Stars with the Roman Space Telescope

“…If one insists on explaining the UHZ1 data with this, "low" mass seeds, such as those generated by the BHs formed by the collapse of 10-1000 M e Population III unrealistic sustained super-Eddington accretion rates, are necessary (see for, e.g., Figure 4 of Bogdan et al 2023, where a radiative efficiency of η ; 0.1 is assumed). 12 Therefore, the need for heavy, or even SMBH, seeds becomes evident when attempting to explain the mass of the SMBHs powering the most distant quasars (Natarajan et al 2023). Supermassive dark stars are ideal candidates for such massive BH seeds.…”

“…12 A lower radiative efficiency would lead to larger mass of the BH, given the same amount of time and starting with the same seed; we note that η ; 0.1 is the standard value in the literature. 13 We mention here an alternative supermassive BH seed: direct collapse to black holes of very metal-poor low angular momentum gas clouds via dynamical instabilities (Loeb & Rasio 1994;Begelman et al 2006;Lodato & Natarajan 2006;Natarajan et al 2023).…”