Solving a mystery

Credit: NASA, ESA, E. Jullo (JPL/LAM), P. Natara­jan (Yale) and J-P. Kneib (LAM).

Some­times what we can’t see is as impor­tant as what we can. Using new tech­niques, astronomers are help­ing solve the big mys­tery of dark energy in the Uni­verse and per­haps its ulti­mate fate.

Explore the image of Abell 1689 from NASA’s Hub­ble Space Tele­scope. The pur­ple area is the sci­en­tists’ lay­out of grav­i­ta­tional lens made up of both vis­i­ble mat­ter and dark mat­ter. The pur­ple haze is a visu­al­iza­tion. Sci­en­tists use this sort of visual over­lay to help us see what is there but not vis­i­ble. Light from the dis­tant galax­ies is bent by the dark mat­ter in the clus­ter pro­duc­ing arcs and other dis­torted views of the galaxies.

The mas­sive galaxy clus­ter, about 2.2 bil­lion light years from Earth, warps the light of back­ground galax­ies, curv­ing and dis­tort­ing their light. Astronomers call this grav­i­ta­tional lens­ing. Grav­i­ta­tional lens­ing is sim­i­lar to the way a mag­ni­fy­ing lens dis­torts how we see an object. The immense grav­ity from this clus­ter is so strong, it bends the beams of light com­ing from dis­tant galax­ies. The warp­ing of space is a con­fir­ma­tion of Albert Einstein’s the­ory of gen­eral rel­a­tiv­ity. Astronomers were able to study the light from these bent, dim galax­ies. They could recon­struct the path the light takes between the far-off galax­ies before finally reach­ing Earth. Study­ing these paths and the way objects are bent by the galaxy clus­ter offers clues into the geom­e­try of space and any effects from stuff we can­not see, such as dark energy.