Pn. Wilkinson et al., Limits on the cosmological abundance of supermassive compact objects from a search for multiple imaging in compact radio sources, PHYS REV L, 86(4), 2001, pp. 584-587
Using very long baseline interferometry we have searched a sample of 300 co
mpact radio sources for examples of multiple imaging produced by gravitatio
nal lensing; no multiple images were found with separations in the angular
range 1.5-50 milliarcsec. This null result allows us to place a limit on th
e cosmological abundance of intergalactic supermassive compact objects in t
he mass range similar to 10(6)M. to similar to 10(8)M.; such objects cannot
make up more than similar to1% of the closure density (95% confidence). A
uniformly distributed population of supermassive black holes forming soon a
fter the big bang does not, therefore, contribute significantly to the dark
matter content of the Universe.