A research team has used gravitational lensing of the MGJ0414+0534 system observed by ALMA to map the distribution of dark matter in unprecedented detail, confirming the theory of cold dark matter and paving the way for further discoveries of the dominant but elusive component of the universe.

Dark matter fluctuations in lens system MGJ0414+0534. The blue and white colors represent the gravitational lensing images observed by ALMA. The calculated distribution of dark matter is shown in orange; lighter areas indicate higher concentrations of dark matter, and darker orange areas indicate lower concentrations. Source: ALMA (ESO/NAOJ/NRAO), K.T.Inoueetal.

New research reveals the distribution of dark matter in unprecedented detail, down to a minimum scale of 30,000 light-years. The observed distribution fluctuations provide better constraints on the properties of dark matter.

The mysterious dark matter makes up most of the matter in the universe. Dark matter is invisible and its existence is only known through gravitational effects. Dark matter has never been isolated in a laboratory, so researchers must rely on "natural experiments" to study it.

Gravitational lensing is a type of natural experiment. Sometimes, by random chance, two objects at different distances in the universe will be on the same line of sight as seen from Earth. When this happens, the curvature of space caused by the material surrounding the foreground object acts like a lens, bending the light paths of the background object, creating a lensed image. However, it is difficult to achieve high resolution in natural experiments to detect dark matter clumps with masses smaller than galaxies, so the exact nature of dark matter has not been well confirmed.

Concept diagram of the gravitational lensing system MGJ0414+0534. Dark matter associated with lensed galaxies appears in pale blue and white. Dark matter in intergalactic space is shown in orange. The solid line shows the actual path of a radio wave bent by gravity. The dashed line indicates the apparent observation location of the lens image. Image source: NAOJ, K.T.Inoue

A Japanese research team led by Kaiki Taro Inoue, a professor at Keiyo University in Japan, used ALMA (Atacama Large Millimeter/submillimeter Array) to study a gravitational lensing system called MGJ0414+0534 in the direction of Taurus. In this system, due to the gravitational effect of the massive galaxy on the light, the foreground object forms not one, but four background objects. Using the bending effect and new data analysis methods, the research team was able to detect fluctuations in the distribution of dark matter along the line of sight with unprecedented high resolution, down to a minimum scale of 30,000 light-years.

The new constraints provided by our observed distribution of dark matter are consistent with models of slow-moving or "cold" dark matter particles. In the future, the research team plans to further constrain the properties of dark matter through more observations.