Kavli Affiliate: Debora Sijacki
| First 5 Authors: Roberto Maiolino, Roberto Maiolino, , ,
| Summary:
The recent discovery of a large number of massive black holes within the
first two billion years after the Big Bang, as well as their peculiar
properties, have been largely unexpected based on the extrapolation of the
properties of luminous quasars. These findings have prompted the development of
several theoretical models for the early formation and growth of black holes,
which are, however, difficult to differentiate. We report the metallicity
measurement around a gravitationally lensed massive black hole at redshift 7.04
(classified as a Little Red Dot), hosted in a galaxy with very low dynamical
mass. The weakness of the [OIII]5007 emission line relative to the narrow
H$beta$ emission indicates extremely low metallicity, less than $10^-2$
solar. We argue that such properties cannot be uncommon among accreting black
holes around this early cosmic epoch. Explaining such a low chemical enrichment
in a system that has developed a massive black hole is challenging for most
theories. Models assuming heavy black hole seeds (such as Direct Collapse Black
Holes) or super-Eddington accretion scenarios struggle to explain the
observations, although they can potentially reproduce the observed properties
in some cases. Models invoking "primordial black holes" (i.e. putative black
holes formed shortly after the Big Bang) may potentially explain the low
chemical enrichment associated with this black hole, although this class of
models also requires further developments for proper testing.
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