Definition:
gravitationally collapsed objects that preclude escape from
their surface
Mass:
~ 100 million solar masses
Size:
less than the solar system
Location:
the nuclei of many galaxies, both active and dormant
Identification:
via the rapid motion of radiating matter tightly orbiting around
the black hole as revealed by optical, radio and X-ray spectral line features,
especially definitive with upcoming X-ray missions
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What is their origin?
A problem:
The mass characteristic of the earliest gravitationally
bound "seed" objects is much too small.
A plausible solution:
initial radiationless rapid growth via the smothering accretion
of amply available ambient matter, ended by a likely X-radiating phase
of slower growth.
An experiment:
investigate the faintest individual sources of the presently unresolved
residual cosmic X-ray background for evidence of a large new population
signaling the birth of supermassive black hole galactic nuclei.
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