Ninety-six per cent of the universe is in a form we can’t find or understand.
Observations of galaxies show they are rotating too fast to hold all their stars in place
The only explanation is that there is an extra gravitational pull from something unseen, holding them in place.
The unseen stuff is known as dark matter, and accounts for just under a quarter of the mass in the universe. But don’t be fooled, it isn’t real until it has been discovered. Currently, it’s just an idea.