Gravitational Lensing

What you are seeing: a point-mass gravitational lens at the origin bends light rays. Choose "lensed image" to see a striped pattern pulled back through the inverse lens map, with yellow dots marking the discrete image positions of a point source. Switch to "extended source" to visualize how a finite-size circular galaxy gets stretched and magnified into arcs or a complete Einstein ring when source and lens align. Drag the canvas to move the source

Figure 1. Image-plane lensed view of a stripe pattern. The yellow points are the two solved point-mass images of the source (red dot). The dashed ring is the Einstein radius. Method: closed-form point-mass lens equation; numerical Jacobian for magnification field.

β_x0.30

β_y0.10

viewlensed

source radius0.08

u_min0.20

shear γ0.25

WHAT TO TRY

Drag the source position beta toward the lens: the two images stretch and brighten, and at perfect alignment they merge into a full Einstein ring. The magnification readout spikes.
Switch to the extended-source view: a finite source is sheared into arcs, the giant luminous arcs that galaxy clusters produce from background galaxies.
Add external shear gamma: the ring distorts into an ellipse and the images shift, the effect of the surrounding mass distribution that lens modelling must fit.