Marked JWST image

Why do the circled galaxies seem to form long circular arcs that surround the white point at the center? And why do most of the galaxies in this image seem to be facing that same point? What is in that point?

  • 13
    $\begingroup$ Search term: "gravitational lensing" $\endgroup$
    – rob
    Jul 12 at 7:14
  • 3
    $\begingroup$ @rob or Einstein Ring, even. $\endgroup$
    – JEB
    Jul 12 at 7:57
  • $\begingroup$ I know about lensing, but does it mean that all the light in this picture is lensed around the mass in the center? $\endgroup$
    – bloop
    Jul 12 at 9:10
  • 3
    $\begingroup$ The light from objects behind the cluster is lensed, Other light isn't. $\endgroup$
    – John Doty
    Jul 12 at 16:47
  • 1
    $\begingroup$ Would be interesting to see this image separated into layers by distance $\endgroup$
    – bloop
    Jul 12 at 21:11

1 Answer 1


The image is that of distant galaxies being gravitationally lensed by a foreground (though still very distant) cluster of galaxies. The paths of the light from the distant galaxies are bent by the spacetime curvature caused by the mass in the foreground cluster.

The distorted images are those of the background galaxies. The distortions in their shapes tells you something about the distribution of mass in the foreground lensing object. In this case, the distortions are mostly tangential to a central point, which reveals (perhaps unsurprisingly) that the mass in the foreground object has a distribution that is roughly spherically symmetric and concentrated towards a central point, which is marked by a large, dominant, central elliptical galaxy in the image. Careful analysis of the shape and brightness of the distroted galaxies can reveal the relative distribution of "normal", luminous matter and dark matter in the foreground cluster.

  • 10
    $\begingroup$ Selecting an area which shows great gravitational lensing was definitely on purpose. It even helps to magnify or brighten some distant objects. The lensing effect of the foreground galaxy cluster (SMACS 0723) was already known. $\endgroup$
    – g.kertesz
    Jul 12 at 15:16
  • $\begingroup$ Do we know the angular size of that image? nasa.gov/image-feature/goddard/2022/… says "image covers a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground", but I don't know how to convert that to arcseconds. ;) jwst-docs.stsci.edu/jwst-observatory-characteristics/… appears to have some relevant info, but I guess we need more details. $\endgroup$
    – PM 2Ring
    Jul 14 at 3:24

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