Dark matter is one of the most mysterious things in existence. We can't see it or feel it, and yet it is threaded through the structure of the Universe, making up around 85 per cent of its mass.
It’s the sheer quantity of dark matter woven through the cosmos that allows astronomers to detect the presence of this otherwise invisible substance.
While it doesn’t interact with light, the gravitational pull of all that dark matter affects the matter we can see, like stars and gas. In fact, its gravity is one of the most important ingredients in making galaxies and prevents them from spinning themselves apart.
It’s such an important ingredient that it could be possible for a galaxy to be made entirely of dark matter. It sounds like a bonkers theory, but astronomers think these ‘dark galaxies’ exist. What’s more, they could be the key to unlocking just what this mysterious matter is.
One of the big successes of the cold dark matter concept is that it's so simple to model - Image credit: NASA/ESA
