Researchers at the University of Waterloo in Waterloo, Ontario, claim to have obtained the first composite image of something that, although being discussed by astronomers for decades, has remained unseen and, in fact, undetected. It’s thought to be an image of dark matter, a link in the enormous cosmic web in which our universe’s billions of galaxies are thought to be embedded. The new work was published in the peer-reviewed Monthly Notices of the Royal Astronomical Society, said in an statement:
Dark matter filaments bridge the space between galaxies in this false-color map. The white regions depict the locations of bright galaxies, while the presence of a dark matter filament spanning the galaxies is shown in red. Image via RAS/ S. Epps & M. Hudson / University of Waterloo.
The composite image, which combines several individual photographs, confirms expectations that galaxies around the universe are connected by a cosmic network connected by dark matter that was previously unobservable.
If this research is accepted – and replicated – by other astronomers, then it flies in the face of other astronomers’ suggestions that perhaps dark matter doesn’t exist, or doesn’t exist in the way we think it exists, after all.
Why do astronomers believe in dark matter? After all, prior to this image, no one has ever claimed to have observed it directly, much less captured its image. Yet dark matter has an honored place in astronomical theory; it’s an integral part of the Lambda Cold Dark Matter model, also known as the standard model of Big Bang cosmology, which is a widely accepted model of how our universe works and agrees well with what astronomers believe they see when they look out into deep space.
Some astronomers think that we either don’t understand dark matter or that it doesn’t exist at all. For example, physicist Erik Verlinde at University of Amsterdam released the latest installment of his new theory of gravity, in which he said he doesn’t need dark matter to explain the motions of stars in galaxies.
Soon after, a team led by astronomer Margot Brouwer of the Leiden Observatory in the Netherlands tested Verlinde’s theory by investigating the gravity lensing effect of over 33,000 galaxies. Her team concluded that Verlinde’s theory “agrees well” with the observations.
That sort of one-two punch is often seen in astronomy. A theory implies something, and observations support it (or not). Of course, the theories and observations are always flawed and imperfect. What else could they be? Scientists would have to be gods to comprehend the workings of the universe perfectly.
And so what you’re likely to see in the weeks and months and years ahead are other astronomers either agreeing or disagreeing that this image represents what researchers at the University of Waterloo say it represents.
According to the most accepted theories of the universe, dark energy is thought to contribute 73 percent of all the mass and energy in the universe. Another 23% is dark matter, leaving only 4% of the universe made up of normal matter like stars, planets, and people. Pie chart via NASA.
In the meantime, know that – according to the most popular models of the universe – dark matter comprises about a quarter of the “stuff” of our universe. This mysterious substance doesn’t shine, absorb or reflect light, although its effects are thought to be recognizable via the workings of gravity.
According to these hypotheses, dark matter is essential in the formation of the cosmic web, the fundamental structure of our universe. This enormous web, in reality, is assumed to be a network of dark matter filaments. Mike Hudson, the University of Waterloo astronomy professor who led this research said of his team’s work:
For decades, researchers have been predicting the existence of dark-matter filaments between galaxies that act like a web-like superstructure connecting galaxies together. This image shifts us away from predictions and toward something we can see and measure.
This often-seen image is an artist’s illustration of a honeycomb-like structure, sometimes called the “cosmic web.” The bright areas are galaxy clusters and groups, with sparsely populated regions devoid of galaxies in between. Because astronomers now believe that galaxies are formed by dark matter merging and clumping together, and because dark matter is thought to be far more abundant in our universe than the type of matter that composes stars and galaxies (and planets like Earth, and people like you and me), dark matter is what is thought to drive the cosmic web’s structure. Image via Volker Springel, Virgo Consortium.
How did the astronomers at the University of Waterloo obtain their image of dark matter? Hudson and co-author Seth Epps, a master’s student at the time, utilized a technique known as weak gravitational lensing, which allows images of distant galaxies to warp slightly due to the influence of an unseen mass such as a planet, a black hole, or – in this case – dark matter. They claimed to have measured the effect in photos from a multi-year sky survey at Mauna Kea’s Canada-France-Hawaii Telescope.
They combined lensing photos from over 23,000 galaxy pairs 4.5 billion light-years apart to create this composite image or map, which they claim shows the presence of dark matter between the two galaxies. In other words, it’s a dark matter bridge, according to these astronomers. Their results suggest that the dark matter filament bridge is strongest across systems distant by fewer than 40 million light years. Epps said:
By using this technique, we’re not only able to see that these dark matter filaments in the universe exist, we’re able to see the extent to which these filaments connect galaxies together.
Let us now examine if other astronomers can replicate these findings and if others concur. If they do, wow … it’s amazing!