I am looking into the effects of gravitational lensing of gravitational waves. I know that gravitons travel along null geodesics, just as photons, and so they will suffer the same deflection angle by a massive close to their paths

I think I know what microlensing is, with the impact parameter, Einstein angle, and amplification factor. However, I have read that weak lensing is likely to be a problem for advanced gravitational wave detectors.

Is weak lensing just the statistical, overall effect of many different microlensing events, or is it something else?


2 Answers 2


Weak Lensing, Strong Lensing and Microlensing are all forms of gravitational lensing---in which observed images of a distant object are affected by the gravitational field of an intervening, more nearby object.

Strong Lensing: Is when the lensing is pronounced enough that multiple images, or an Einstein ring is apparent.

Weak Lensing: is when the image shape or position is noticeably altered, but there is still only one image (often in practice this means that the lensed image can be considered as a perturbation to the un-lensed image).

Microlensing: is when only the magnitude of light is altered (i.e. it is a photometric, instead of an astrometric effect).

Strong Lensing----In this case, a single galaxy has been distorted into an almost complete Einstein ring.


Weak Lensing---In this simulated example, the shape of many objects is noticeably altered by the foreground (not shown) mass distribution.

enter image description here

Microlensing---This schematic is meant to illustrate that only the apparent brightness of the object is effected, while its apparent position and shape (in general such an object would be unresolved) remain the same.

enter image description here


A great example of microlensing allowing us to view an otherwise invisible star. The Star Icarus after microlensing

From Popular Science: "The blue giant star is about twice as hot as the Sun and was only visible because all the stars aligned. No, really. This star’s light was already magnified about 600 times by a cluster galaxy positioned between the star and the Hubble telescope. But when a star about the size of our sun within that galaxy passed between the object and Hubble, the magnification skyrocketed. It now appeared 2000 times brighter than it normally would, a phenomenon known as microlensing. The astronomers nicknamed the early star Icarus."

  • $\begingroup$ I'm confused. Is the lensed star the big blue one, or the one pointed to? It seems like it would be the latter, but that's not what the description says. $\endgroup$
    – Javier
    Apr 3, 2018 at 17:35
  • $\begingroup$ @Javier The quote is from an article, not a caption on the photo. "The blue giant star" is the faintly visible, lensed item. The large blue star toward the bottom of the photo is not associated. $\endgroup$
    – BowlOfRed
    Apr 3, 2018 at 17:40
  • $\begingroup$ The blue star with the colorful diffraction spikes is probably a foreground star, within the Milky Way The object of interest here, whose blue color is not visible in the greyscale inset images, is at the location indicated by the arrow. $\endgroup$
    – rob
    Apr 3, 2018 at 17:41
  • $\begingroup$ @BowlOfRed Thanks, that makes sense. The word "giant" confused me, I thought they meant that it looks giant in the picture. $\endgroup$
    – Javier
    Apr 3, 2018 at 17:44
  • $\begingroup$ It's the one pointed to by the arrow. Not visible in 2011 but suddenly visible in 2016. All because another star passed in front and microlensed the image to make it 2000 time brighter. And it all happened some 9 billion years ago. $\endgroup$ Apr 3, 2018 at 17:44

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