Astronomers have found an invisible object in the Universe weighing just a million Suns — for cosmic scales, that’s a mere trifle, a hundred times lighter than anything they’ve been able to “weigh” at such distances. The object itself doesn’t shine, but it gave itself away by bending the light from an even more distant galaxy. Massive bodies, as Einstein showed, warp spacetime and act like lenses: just as a transparent bead on a window distorts the outline of a streetlamp.
In this case, the invisible object became that bead.
It’s likely either a faint dwarf galaxy, almost devoid of stars, or a clump of dark matter — that enigmatic substance first suspected after the observations of Vera Rubin. Catching such invisible things means probing the hidden scaffolding of the Universe and understanding how giant galaxies like our Milky Way grew.
This object’s mass — roughly a million Suns — is a drop in the ocean by cosmic standards. For comparison, the Milky Way is a million times heavier, weighing in at about a trillion Suns.