Our galaxy moves through space

What moves the Milky Way

The Milky Way is not only attracted to a huge collection of galaxies, but also repelled by a gigantic empty region. This is shown by the most extensive and precise analysis of galaxy movements in our cosmic environment by an international team of researchers to date. The empty region is about 600 million light years away and 400 million light years in size. Together with the Shapley supercluster 700 million light years away, the empty region produces a dipole field similar to a magnet in which the galaxies move, the scientists write in the journal "Nature Astronomy".

Galaxy movement

“Our local group of galaxies moves relative to the cosmic background radiation at a speed of 630 kilometers per second,” explain Yehuda Hoffman from the Hebrew University of Jerusalem and his colleagues. “This galaxy flow stretches for more than 800 million light years.” The main cause of this joint movement of the galaxies has long been viewed by astronomers as the “Great Attractor”, a collection of galaxy clusters 150 million light years away.

Then the sky researchers discovered an even larger structure behind the Great Attractor, the Shapley Supercluster, 700 million light-years away, which contains over two dozen large galaxy clusters. But even with this cosmic superstructure, the motion of the Milky Way and its neighboring galaxies could not be satisfactorily explained. Researchers have long suspected that a large region in which there are hardly any galaxies also plays a role. However, the detection of such a "void" has so far proven to be far more difficult than the detection of large collections of galaxies.

Hoffman and his colleagues therefore took a different approach: instead of looking for galaxies directly and mapping their density, they examined the cosmic velocity field of the galaxies with great accuracy. Because this flow field is created by the force of gravity of the surrounding accumulations of matter and thus reflects the distribution of the matter and thus also of the galaxies. In this way, Hoffman and his colleagues were able to deduce the existence of a large empty space from the flow field, which lies opposite the Shapley attractor and forms a kind of dipole with it. Hoffman and his colleagues hope that extremely sensitive sky surveys in the optical, infrared and radio range will also be able to directly demonstrate this great void in a few years.