title: Limits on the cosmological abundance of supermassive compact objects from a search for multiple imaging in compact radio sources.
abstract: Using very long baseline interferometry we have searched a sample of 300 compact radio sources for examples of multiple imaging produced by gravitational 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 the cosmological abundance of intergalactic supermassive compact objects in the mass range approximately 10(6)M( middle dot in circle) to approximately 10(8)M( middle dot in circle); such objects cannot make up more than approximately 1% of the closure density ( 95% confidence). A uniformly distributed population of supermassive black holes forming soon after the big bang does not, therefore, contribute significantly to the dark matter content of the Universe.
authors.affiliation: University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, United Kingdom.
authors.forename: P N
authors.initials: PN
authors.lastname: Wilkinson
authors.forename: D R
authors.initials: DR
authors.lastname: Henstock
authors.forename: I W
authors.initials: IW
authors.lastname: Browne
authors.forename: A G
authors.initials: AG
authors.lastname: Polatidis
authors.forename: P
authors.initials: P
authors.lastname: Augusto
authors.forename: A C
authors.initials: AC
authors.lastname: Readhead
authors.forename: T J
authors.initials: TJ
authors.lastname: Pearson
authors.forename: W
authors.initials: W
authors.lastname: Xu
authors.forename: G B
authors.initials: GB
authors.lastname: Taylor
authors.forename: R C
authors.initials: RC
authors.lastname: Vermeulen