ASTRO In the literature: open

Were the first black hole seeds light or heavy?

In plain words

The first black holes could have started as remnants of the first stars (tens to hundreds of solar masses) or as gas clouds collapsing directly into black holes of 10,000 to a million solar masses. Which happened sets everything that followed.

Precise statement

Determine the mass function of black hole seeds formed at $z \sim 15-30$: light seeds ($M \sim 10-10^{3}\,M_{\mathrm{sun}}$, Population III remnants), intermediate seeds from runaway mergers in dense star clusters ($M \sim 10^{3}-10^{4}\,M_{\mathrm{sun}}$), or heavy seeds from direct collapse of metal-free atomic-cooling gas ($M \sim 10^{4}-10^{6}\,M_{\mathrm{sun}}$). An answer is the seed mass function, or a demonstration that one channel dominates the progenitors of the $z > 6$ quasar and broad-line AGN population.

What would settle it

Detection and mass measurement of accreting black holes with $M_{\mathrm{BH}} \sim 10^{4}-10^{6} M_{\mathrm{sun}}$ at $z>10$ (JWST plus deep X-ray imaging), or the redshift and mass distribution of massive black hole mergers measured by the LISA gravitational-wave mission.

Status in the literature

Unverified note

The 2023-2024 X-ray detection of an AGN in UHZ1 at $z \sim 10.1$ with $M_{\mathrm{BH}}$ of approximately $4x10^7\,M_{\mathrm{sun}}$ was argued to favor heavy seeds, but light seeds with super-Eddington growth are not excluded.