Astronomers Detect Smallest Known Clump of Pure Dark Matter Using Gravitational Lensing

Astronomers have found what could be the smallest clump of pure dark matter yet detected. The object has about one million times the mass of our Sun, yet emits no light. It lies roughly 10 billion light-years away and was spotted through a tiny gravitational distortion in an Einstein ring (a ring-shaped gravitational lens) around a more distant galaxy. Its apparent lack of stars suggests a “pure” dark matter clump without any luminous matter.

Gravitational lensing reveals hidden mass

According to two separate papers, the Einstein ring was imaged into unprecedented detail with a global array of radio telescopes used by astronomers. Detailed algorithms were then used to create a gravity map of the lensing image and exposed a small notch in the radio emission of the ring. Such a small distortion can not be induced by anything that is not visible and its mass is approximately one million solar masses. That is approximately 100 times lighter than the lightest object observed by this method.

New directions for dark matter research

The fact that the object does not emit any light makes astronomers prefer a dark-matter clump explanation to an ordinary galaxy. Assuming this, it would represent the smallest such dark-matter halo so far revealed - more than 100 times lighter than the lightest known. Cold dark matter models have slowly moving particles capable of forming small starless halos.

The discovery of this single clump is not surprising as per theory: the identification is which the authors of the study, Devon Powell, explained that they expect that more should be discovered by astronomers. According to Chris Fassnacht, a member of the team, the discovery of low-mass objects plays a crucial role in learning the nature of the dark matter.