A mysterious 'void' is pushing the Milky Way through the universe at 1.2 million miles per hour

The force that propels the Milky Way's race through space has been a mystery
It used to be thought a dense collection of galaxies was pulling on our own
But a new study has found an extragalactic void is also pushing us away

Published: 11:00 EST, 30 January 2017 | Updated: 11:35 EST, 30 January 2017

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You may not realise it, but you can never stay still – we live on a planet that spins on its axis, orbiting a star that itself is orbiting a galaxy that moves at an immense speed.

It used to be thought our galaxy moved so quickly because it was being pulled towards a dense region of the universe, by that region's gravity.

But a new study has shown the Milky Way is also being pushed through the universe by an extragalactic void, in a kind of galactic tug-of-war.

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By 3D mapping the flow of galaxies through space, the researchers showed that the Milky Way is simultaneously repelled by a region called the Dipole Repeller, and attracted by the Shapley Concentration

MOVING THROUGH SPACE

The Earth spins on its axis at 994 mph (1,600 km/h) and it orbits around the sun at 62,000 mph (100,000 km/h).

Meanwhile, the sun orbits our Milky Way galaxy at 530,000 mph (850,000 km/h), and the galaxy itself moves with respect to the universe at around 1.2 million miles per hour (2 million km/h).

The force propelling the Milky Way through space has been a mystery to scientists for decades - but now a new 3D map has shed light on the mystery.

Previously it was thought a dense region of the universe was pulling us toward it, through the sheer might of its gravity - with a gravitational force equivalent to a million billion suns.

This initial suspect was called the Great Attractor, a region of clusters of galaxies 150 million light years from the Milky Way.

Now researchers at the Hebrew University of Jerusalem report that our galaxy is not only being pulled, but also pushed.

A new study has shown the Milky Way is also being pushed through the universe by an extragalactic void, in a kind of galactic tug-of-war

In a new study published in Nature Astronomy, the researchers describe a previously unknown, very large region in our extragalactic neighbourhood.

Largely empty of galaxies, this 'void' exerts a repelling force on our Local Group of galaxies, the researchers say.

'By 3D mapping the flow of galaxies through space, we found that our Milky Way galaxy is speeding away from a large, previously unidentified region of low density,' said Professor Yehuda Hoffman, lead author of the paper.

As well as being pulled towards the known Shapley Concentration, galaxies including Laniakea, Perseus-Pisces and our own Milky Way are also being pushed away from the newly discovered Dipole Repeller

THE GREAT ATTRACTOR

Somewhere in the far reaches of space lies an object that is pulling everything, including our galaxy, towards it with a gravitational force equivalent to a million billion suns.

When it was discovered in 1970 it was named the 'great attractor' because of its effect on everything nearby, although exactly what it is made of has remained a mystery because the disk of our own galaxy blocks our view to it.

The great attractor is not an object but a instead point in the centre of the supercluster of galaxies in which our Milky Way sits, Dr Paul Sutter, an astrophysicist at Ohio State University, said.

'Because it repels rather than attracts, we call this region the Dipole Repeller.

'In addition to being pulled towards the known Shapley Concentration, we are also being pushed away from the newly discovered Dipole Repeller.

'Thus it has become apparent that push and pull are of comparable importance at our location.'

The presence of a low density region has been suggested previously, but confirming the absence of galaxies by observation has proved challenging.

Using powerful telescopes, including the Hubble Space Telescope, the researchers created a 3D map of the universe.

The scientists studied the velocities of galaxies around the Milky Way, and inferred the underlying mass distribution of dark matter and luminous galaxies.

This 3D map was used to identify the Dipole Repeller, so the researchers were able to reconcile both the direction of the Milky Way's motion.

Using powerful telescopes, including the Hubble Space Telescope, the researchers created this 3D map of the universe. Using this map, the researchers were able to identify the Dipole Repeller, allowing them to reconcile both the direction of the Milky Way's motion