Dark matter: The mysterious substance that makes up 27% of the universe that scientists cannot confirm
Dark matter is a hypothetical substance said to make up roughly 27 per cent of the universe.
The enigmatic material is invisible because it does not reflect light, and has never been directly observed by scientists.
Astronomers know it to be out there because of its gravitational effects on known matter.
The European Space Agency says: 'Shine a torch in a completely dark room, and you will see only what the torch illuminates.
'That does not mean that the room around you does not exist.
'Similarly we know dark matter exists but have never observed it directly.'
The material is thought to be the gravitational 'glue' that holds the galaxies together.
Calculations show that many galaxies would be torn apart instead of rotating if they weren't held together by a large amount of dark matter.
Just five per cent the observable universe consists of known matter such as atoms and subatomic particles.