Milky Way contains a disk of 'dark matter', say scientists

London, September 17 : An international team of scientists has predicted that our galaxy, the Milky Way, contains a disk of 'dark matter'.

The team includes astronomers Dr Justin Read, Professor George Lake and Oscar Agertz of the University of Zurich, and Dr Victor Debattista of the University of Central Lancashire, who have used the results of a supercomputer simulation to deduce the presence of this disk.

They have explained how the simulation could allow physicists to directly detect and identify the nature of dark matter for the first time.

Unlike the familiar 'normal' matter that makes up stars, gas and dust, 'dark' matter is invisible but its presence can be inferred through its gravitational influence on its surroundings.

Physicists believe that it makes up 22 per cent of the mass of the Universe, compared with the 4 per cent of normal matter and 74 per cent comprising the mysterious 'dark energy'.

But, despite its pervasive influence, no one is sure what dark matter consists of.

Prior to this work, it was thought that dark matter forms in roughly spherical lumps called 'halos', one of which envelopes the Milky Way.

But, this 'standard' theory is based on supercomputer simulations that model the gravitational influence of the dark matter alone.

The new work includes the gravitational influence of the stars and gas that also make up our Galaxy.

Stars and gas are thought to have settled into disks very early on in the life of the Universe and this affected how smaller dark matter halos formed.

The team's results suggest that most lumps of dark matter in our locality merged to form a halo around the Milky Way, but the largest lumps were preferentially dragged towards the galactic disk and were then torn apart, creating a disk of dark matter within the Galaxy.

"The dark disk only has about half of the density of the dark matter halo, which is why no one has spotted it before," said lead author Justin Read.

"However, despite its low density, if the disk exists it has dramatic implications for the detection of dark matter here on Earth," he added.

The 'wind' from the dark disk is much slower than from the halo because the disk co-rotates with the Earth.

This abundance of low-speed dark matter particles could be a real boon for researchers because they are more likely to excite a response in dark matter detectors than fast-moving particles.

This new research raises the exciting prospect that the dark disk - and dark matter - could be directly detected in the very near future.

ANI