Astronomers Now Have An Image Of The Dark Matter Web They Always Thought Was There

Brilliance | Dec. 09, 2017

If something can't emit, reflect, or absorb light, how do you know it's there? That's the conundrum that surrounds dark matter, the elusive substance that scientists believe makes up a whopping 27 percent of the universe. In April 2017, we may have answered that question: researchers at the University of Waterloo created the first composite image of the dark matter that connects galaxies together. That little pink-and-purple graphic is what scientific breakthroughs are made of.

Pics Or It Didn't Happen

There's only one piece of evidence dark matter provides of its existence: gravity. That's what Waterloo researchers Mike Hudson and Seth Epps relied upon to create their image. See, gravity bends light. The more massive the object, the more gravity it exerts and the more the light behind it warps in a phenomenon called gravitational lensing. The team collected gravitational lensing data from a multi-year sky survey at the Canada-France-Hawaii Telescope, then they got another collection of data in the form of background source galaxies from the Sloan Digital Sky Survey that had accurate measurements of distance. Those galaxies were specifically bright, massive ones called luminous red galaxies, chosen because the astronomers expected their large mass to translate into a large dark-matter bridge.

Once they had the two data sets, they picked out 23,000 galaxy pairs that they knew were physically close to each other—rather than ones that only look that way in the sky—all located about 4.5 billion light-years away. After combining the lensing data with the background source data, they took an average of all 23,000 pairs to create a composite image that plainly shows the presence of dark matter between galaxies.

Chasing The Invisible Dragon

What does this mean for the future of astronomy? A lot. Ever since the existence of dark matter was proposed in the 1930s, scientists have been looking for clues that would help us know more about it. Even recently, as the team notes in their paper, dozens of scientists have attempted to measure the web of dark matter that was predicted to bridge galaxies. "This image moves us beyond predictions to something we can see and measure," Hudson said in a statement. The researchers' new technique could be the foundation for many more discoveries about dark matter.

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