The mystery of dark matter has been a challenge for scientists, who know that the substance must exist in our universe but have been unable to find a way to identify it. As it does not give out any kind of electromagnetic radiation, dark matter can only be detected due to its gravitational effects. Now two astronomers from the University of New South Wales, Australia and the Instituto de Astrofísica de Canarias, Spain, have come up with a method to “see” dark matter by looking at the distribution of starlight in galaxy clusters.
The astronomers used data from the Hubble telescope to look at a faint source of light called intracluster light, which is caused by the interactions of galaxies. When two galaxies interact, stars can be ripped away from their home galaxy and float freely within the cluster, giving off faint light. It is known from mathematical models of clusters that the majority of the mass of the cluster is made up of dark matter, and these free-floating stars end up in the same location that the dark matter is believed to be found. “These stars have an identical distribution to the dark matter, as far as our current technology allows us to study,” one of the researchers, Dr. Mireia Montes, explains.
This means that the intracluster light given off by these isolated stars could be used as an indicator for the location of dark matter as the stars follow the gravity of the cluster. This would be a much more efficient way of tracing dark matter than other methods like gravitational lensing as it only requires the use of deep imaging like that provided by Hubble.
In addition to providing a way to track dark matter, this work could also be useful in understanding what sort of substance it is. “If dark matter is self-interacting we could detect this as tiny departures in the dark matter distribution compared to this very faint stellar glow,” another researcher, Dr. Ignacio Trujillo says. If it is the case that dark matter self-interacts, that would be a significant step forward in our understanding of what it is and how it interacts with regular matter.
The next step for the researchers is to use the Hubble data to see if their method works for other clusters as well.