Angular diameters as a probe of a cosmological constant and Ω

Lawrance M. Krauss, David N. Schramm

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The lensing effect of curved space, which can cause the angular diameter of a fixed reference length seen on the sky to reach a minimum and then increase with redshift, has recently been claimed to provide evidence, using compact radio sources, for a q0 = 1/2 expansion. We show here that this relation, in particular the position of the observed minimum, depends sensitively on the value of the cosmological constant, Λ, in a flat universe. The sensitivity to a nonzero Λ in a flat universe is compared to the sensitivity to q0 in an open universe without a cosmological constant. The reported results could provide the strongest available limit on the cosmological constant in a flat universe (and on Ω in an open universe) and so we explore how uncertainties in distance measures and evolution of the sources can affect the results. Evolution of less than 30% in source size for z ≤ 2 can completely alter the results, and so must be convincingly ruled out if this technique is to provide a new tool for cosmology.

Original languageEnglish (US)
Pages (from-to)L43-L46
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - Mar 10 1993
Externally publishedYes


  • Cosmology: theory

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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