For decades, scientists have tracked hints of a thread-like structure that ties together galaxies across the universe. Theories, computer models, and indirect observations have indicated that there is a cosmic web of dark matter that connects galaxies and constitutes the large-scale structure of the cosmos. But while the filaments that make up this web are massive, dark matter is incredibly difficult to observe.
Now, researchers have produced what they say is the first composite image of a dark matter filament that connects galaxies together.
“This image moves us beyond predictions to something we can see and measure,” said Mike Hudson, a professor of astronomy at the University of Waterloo in Canada, co-author of a new study published in the Monthly Notices of the Royal Astronomical Society.
Dark matter, an elusive substance that is estimated to make up around 27 percent of the universe, doesn’t give off, reflect, or absorb light. This has made it virtually impossible to detect, except for its effects when it exerts a gravitational tug or when it warps the light of distant galaxies in what is called gravitational lensing.
For their work, Hudson and co-author Seth Epps, who was a master’s student at the University of Waterloo at the time of the research, employed a technique called weak gravitational lensing — a statistical measurement of the slight bends that occur in the path of light passing near mass. The effect produces illustrations of galaxies that appear slightly warped owing to the presence of celestial mass, such as dark matter.