Seeing the Unseeable

The theory that birthed the concept of dark matter came to be out of necessity. Based on the matter we can see, our universe shouldn't be able to exist and operate as it does — this visible matter can't generate the gravity necessary to keep our galaxies held together. Dark matter is a way for scientists to account for this discrepancy. They posit that our universe must contain a kind matter that we cannot see, a kind that doesn't absorb, reflect, or emit light — a truly dark matter.

For our scientific models to hold true, dark matter must make up more than a quarter of all the matter in the universe. Still, what dark matter is actually made of remains a mystery, and finding evidence of something that cannot be seen is a daunting task. Previously, the gravitational effects of dark matter are the closest thing to proof that scientists have, but now, researchers from the University of Waterloo in Ontario, Canada, have something even better: a composite picture that proves that galaxies are indeed connected by dark matter.

Credit: S. Epps & M. Hudson / University of Waterloo

Using a technique known as weak gravitational lensing, the researchers combined images taken over the course of years to show the presence of dark matter. The composite was created using images from more than 23,000 galaxy pairs situated 4.5 billion light-years away.

The Missing Universe

We may not have greater insight as to exactly what this matter is composed of, but at least we now have a physical representation of its existence between galaxies.

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"For decades, researchers have been predicting the existence of dark-matter filaments between galaxies that act like a web-like superstructure connecting galaxies together," explained Mike Hudson, a professor of astronomy at Waterloo, in a press release from the Royal Astronomical Society. "This image moves us beyond predictions to something we can see and measure."

Indeed, the image is an important step toward legitimizing dark matter and dark energy at a time when other scientists are proposing models that would do away with the need for dark matter to exist entirely. It brings us closer to understanding dark matter and the role it plays in binding the universe together. Existence is an infinitely large puzzle comprising innumerable pieces. Any time we can find a way to connect those pieces we bring the big picture into greater focus and move one step closer to truly understanding the world in which we live.

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