Hubble’s greatest discoveries: dark matter

Something is hiding in our Universe, and the Hubble Space Telescope could help us find it.

Hubble allowed scientists to create this 3D map of dark matter – the distance from Earth increases from left to right © NASA, ESA and R. Massey (California Institute of Technology)
Hubble allowed scientists to create this 3D map of dark matter – the distance from Earth increases from left to right © NASA, ESA and R. Massey (California Institute of Technology)

This picture reveals the presence of something we can’t see: ‘dark matter’. The galaxies, stars and planets that we can see make up just 15 per cent of the Universe’s matter. The rest – the other 85 per cent – is dark matter and it neither emits nor absorbs any known wavelength of light.

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“With this map, we saw for the first time where dark matteris,” says Durham University physicist Dr Richard Massey. To construct it, half a million galaxies were observed by the Hubble Space Telescope and ground-based telescopes.

“When light travels across the Universe, it passes through all the intervening dark matter on its way to us, leaving a tell-tale imprint of its journey. You can’t see such faraway, faint galaxies from Earth because the atmosphere blurs the detail. This is why we needed Hubble,” explains Massey.

The dark matter bends the light in a ‘gravitational lensing’ effect, making the galaxies appear distorted. By observing this, it’s possible to deduce where dark matter lies. Such a map is fundamental to understanding the Universe’s structure, as dark matter acts as ‘scaffolding’, along which galaxies are assembled.

“When the first explorers reached the American West, they sat on a ridge and tried to understand the lie of the land. We were doing the same thing on a new frontier,” says Massey.

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