What does a walk in the woods have to do with dark matter?

If you take a walk through the woods this fall you will probably notice mushrooms appearing around fallen logs. If you look a little closer, you might also be lucky enough to spot a slime mold. Slime molds, fungi-like organisms that aren’t fungi, are unicellular organisms with some very descriptive names such as dog’s vomit (see image below) and have helped astronomers refine their search for dark matter.













Dark matter, as its name implies, is matter we can’t see in the electromagnetic spectrum, but it has mass and it has a gravitational effect. So, if we can’t see it, why do astronomers think it exists? Because without it, theories about the structure of the universe don’t match observations.

Astronomers use a combination of observations, theory and experimentation to study the universe. As they’ve expanded their understanding of how the universe works, they realized that their observations and the theory do not always agree. An example of this is the speed with which stars move at the edge of a spinning, spiral galaxy. Based on visible matter, the stars at the centre of a galaxy should move much faster than those at the outer edge, but they don’t! If you add more mass, increasing the gravitational influence on objects, then the observation and the theory agree. This added mass, matter we can’t see, is what astronomers call dark matter, and it is important in shaping the large-scale structure of the cosmos.

But back to slime molds and that surprising connection to dark matter and the large-scale structure of the universe. Astronomers noticed the similarity between the behaviour of slime mold as it builds filaments to capture new food and how gravity shapes the cosmic web strands between galaxies and galaxy clusters. The cosmic web consists mostly of dark matter and gas, which becomes the fuel from which new stars develop. They applied the positions of 37000 galaxies to a computer algorithm inspired by slime mold behaviour to produce a three-dimensional map of the intricate filamentary network that makes up the cosmic web.

Our playlist this month is more focused on great background materials to help you deepen your understanding of dark matter. Although there aren’t a lot of hands-on activities related to dark matter, maybe you can use what you’ve learned to inspire a fun costume for International Dark Matter Day, October 31. Send us a photo—we’d love to see what you come up with!


Grow your own slime molds. Read about slime molds and then follow the directions under the “finding wild slime molds” link to grow your own.

Ask yourself: Keep a journal documenting the growth of your slime mold. What surprises you about slime molds?


Read this collection of articles about dark matter.

Ask yourself: After reading the articles what questions do you have about dark matter?


Watch this short video about a recent discovery using images from the Hubble Space Telescope.

Ask yourself: Imagine a more powerful telescope than Hubble. When the James Web Space Telescope becomes operational, how do you think it might change our understanding of the universe?


Read this article to learn more about how astronomers are using slime molds to study dark matter.

Ask yourself: How important do you think creativity is in scientific research?



Curious about the next steps astronomers are taking to detect dark matter? Have a look at this website.

Ask yourself: Which approach to dark matter experiments, direct detection or indirect detection, do you think will be the most successful?