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Thread: Gravitational lensing => cosmological parameters

  1. #1
    Join Date
    Aug 2003
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    Gravitational lensing => cosmological parameters

    Gaia recently found 12 new Einstein crosses. The article also notes that:

    “Quasars are intrinsically variable objects, and because the light in each lensed image has crossed different paths in the Universe, fluctuations in the quasar’s light show up in the images at different times. From this it is possible to estimate the Hubble-Lemaître constant.”

    If I ever did, I have forgotten the logic behind estimating the Hubble constant based on strong gravitational lensing. What's the thumbnail explanation for how to do this?
    Everyone is entitled to his own opinion, but not his own facts.

  2. #2
    Join Date
    Jul 2005
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    20,558
    You need three things--the angular separation of two lensed images, the light-travel time delay between those two lensed images, and the velocity dispersion of stars in the lensing galaxy.
    The last item, providing an estimate of the mass of the lensing galaxy, allows you to calculate a geometrical relationship between separation angles and time delays which scales with the distance of the lensing galaxy. Then you check that against the measured values, and read off a distance. Then you compare this distance (specifically, it's the angular diameter distance) with the redshift.

    Grant Hutchison
    Last edited by grant hutchison; 2021-Apr-13 at 06:56 PM.

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