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I know that gravitational lensing is a geometric effect that occurs when light changes direction because a massive object causes space-time to warp and consequently the radiation rays change the path they are taking. And I also know that thanks to Gaia it is possible to predict gravitational microlensing events, but what would be the objective of predicting this type of event?

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The objective is to calculate the mass of the lensing object.

Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of the lens and the unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Source: Prediction of astrometric microlensing events from Gaia DR2 proper motions

By predicting future lensing events you can be prepared to make careful measurements during the period of gravitational lensing. This allows you to find the mass of the lensing star, which is one of the fundamental properties of a star, but one which can be hard to determine by other methods.

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  • $\begingroup$ Can you cite any evidence of a microlensing event specifically that was predicted? There are predictions of lensing events discussed in Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image? but that's not microlensing. $\endgroup$
    – uhoh
    Jun 21 at 22:58
  • $\begingroup$ I wonder if you looked at my source, or even the first sentence of my quote. "Astrometric gravitational microlensing ..." However here is a specific example of observations of a predicted and observed lensing event ui.adsabs.harvard.edu/abs/2018MNRAS.480..236Z/abstract observations of a microlensing event in which proxima lensed a background star. $\endgroup$
    – James K
    Jun 22 at 4:48
  • $\begingroup$ No, if the source discusses prediction then that bit should be quoted. I've added its title and some key bits to show you what I mean. A Stack Exchange answer should not require folks to go off-site to get the answer if not necessary. $\endgroup$
    – uhoh
    Jun 22 at 7:38
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    $\begingroup$ and you haven't read the question. The question was not "have microlensing events been predicted" but "And I also know that thanks to Gaia it is possible to predict gravitational microlensing events, but what would be the objective of predicting this type of event?" And the answer is written in the answer "To determine the mass of the lensing star". All you have done is copied a mass of additional material to the answer, which is not directly relevant. So I'm reverting. $\endgroup$
    – James K
    Jun 22 at 16:45

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