University of Waterloo

The first image of a dark matter "bridge", believed to form the links between galaxies, has been captured by astrophysicists in Canada.

Researchers at the University of Waterloo used a technique known as weak gravitational lensing to create a composite image of the bridge. Gravitational lensing is an effect that causes the images of distant galaxies to warp slightly under the influence of an unseen mass, such as a planet, a black hole, or in this case, dark matter.


Universe's dark matter skeleton spotted for the first time Filaments Universe's dark matter skeleton spotted for the first time

Their composite image was made up of a combination of combined lensing images taken of more than 23,000 galaxy pairs, spotted 4.5 billion light-years away. This effect was measured from a multi-year sky survey at the Canada-France-Hawaii Telescope.

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These results show that the dark matter filament bridge is strongest between systems less than 40 million light years apart, and confirms predictions that galaxies across the Universe are tied together through a cosmic web of the elusive substance.

Dark matter is known as "dark" because it doesn't shine, absorb or reflect light, which has traditionally made it largely undetectable, except through gravity and gravitational lensing. Evidence for the existence of this form of matter comes, among other things, from the astrophysical observation of galaxies, which rotate far too rapidly to be held together only by the gravitational pull of the visible matter.


Astrophysics has long proposed the Universe's web of stars and galaxies is supported by a "cosmic scaffolding" made up of fine threads of this invisible dark matter. These threadlike strands formed just after the Big Bang when denser portions of the Universe drew in dark matter until it collapsed and formed flat disks, which featured fine filaments of dark matter at their joins. At the cross-section of these filaments, galaxies formed.

University of Waterloo

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

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"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," said co-author Seth Epps.

What is dark matter? Dark matter is an invisible form of matter which, until now, has only revealed itself through its gravitational effects. Evidence for the existence of this form of matter comes, among other things, from the astrophysical observation of galaxies, which rotate far too rapidly to be held together only by the gravitational pull of the visible matter. High-precision measurements using the European satellite Planck show that almost 85 percent of the entire mass of the universe consists of dark matter. All the stars, planets, nebulae and other objects in space that are made of conventional matter account for no more than 15 percent of the mass of the universe. The unknown form of matter can either consist of comparatively few, but very heavy particles, or of a large number of light ones.

One of the possible candidates for dark matter is a particle called the axion, first proposed in 1977. It appears in some extensions of the Standard Model of particle physics. Astronomers believe that if axions make up dark matter, they could be detected through gravitational waves. This is because axions accelerated by a black hole would give off gravitational waves, just as electrons give off electromagnetic waves.

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As a result, instruments like Ligo – and the upcoming Advanced Ligo (Ligo) –

may be able to see gravitational waves (GWs) from thousands of black hole (BH) mergers which would mark the beginning of a new precision tool for physics.

Physicists have a general idea about what the dark matter particle looks like but are struggling to build a clear picture. They can track the distribution of dark matter throughout the galaxy by examining how galaxies move, but can't pinpoint its exact location or design.

Earlier this year, Priyamvada Natarajan, a professor of astrophysics at Yale University, and her team brought the search for dark matter a step forward by creating the most detailed map of dark matter ever created. The map looks like an alien landscape, with uneven peaks and troughs scattered throughout. There are gentle mounds, on top of which sharp peaks arise, like the inside of a cave covered in stalactites.