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Old October 16th 19, 04:49 AM posted to sci.astro.research
Jos Bergervoet
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Posts: 126
Default Is the Universe Younger than We Thought?

On 19/10/15 10:17 PM, Steve Willner wrote:
In article ,
"Jonathan Thornburg [remove -animal to reply]"
writes:

The preprint is 1909.06712


Two additional preprints are at
https://arxiv.org/abs/1907.04869 and
https://arxiv.org/abs/1910.06306

...
...
One other note from the talk: it takes an expert modeler about 8 months
to a year to model a single lens system. Shajib and others are trying
to automate the modeling,


You obviously do not mean that they do it by pencil and paper at this
moment. So why is modeling labor-intensive? Isn't it just putting a
point mass in front of the observed object, which only requires fitting
the precise position and distance of the point mass using the observed
image? (And if so, is the actual imaging with the point mass in some
place the difficult part?) Or is the problem that the lensing object
may be more extended than a point mass? (Or is it something worse!?)

--
Jos

[[Mod. note -- In these cases the lensing object is a galaxy (definitely
not a point mass!). For precise results a nontrivial model of the
galaxy's mass distribution (here parameterized by the (anisotropic)
velocity dispersion of stars in the lensing galaxy's central region)
is needed, which is the tricky (& hence labor-intensive) part.
-- jt]]