Small clouds of dark matter pass through Earth on a regular basis, suggest new calculations. The clouds may be remnants of the first structures to form after the big bang and could be detected by future space missions.
Dark matter interacts gravitationally with normal matter and appears to be seven times more abundant in the universe. But physicists do not know what the mysterious matter is made of or exactly how it is distributed through space.
Nonetheless, they have devised a number of hypothetical dark matter particles that were created in the big bang. These particles formed the universe’s first structures, where mysterious “quantum seeds” caused matter to clump more densely in certain spots. Dark matter slid into these spots which grew into structures that merged to become giant clouds – or haloes – with millions or trillions times more mass than the Sun.
For their study, they used the leading candidate for dark matter, a particle called a neutralino which has the mass of about 100 protons and interacts only weakly with normal matter. Their predicted energies and motions made them settle into structures about 30 million years after the big bang. The structures took the shape of flattened spheres or cigars with diameters about 4000 times the distance between the Earth and Sun.
“We estimate that lots of these small clumps can still survive in the Milky Way,” says Diemand. Perhaps a million billion of them drift around the large dark matter halo that is thought to enclose our galaxy. Such a cloud may float through Earth every 10,000 years in an encounter lasting about 50 years.
But the phantom clouds do not affect the Earth, says Diemand. Their relatively wispy densities mean they could only nudge our planet out of its normal orbit by less than a millionth of a metre per second…