hidden galaxies
February 9, 2016

Astronomers have discovered hundreds of hidden galaxies behind the Milky Way

Hundreds of hidden galaxies located extremely close to the Milky Way, but long obscured by our galaxy itself, have been observed for the first time by an international team of researchers using a specially-equipped radio telescope, according to a new Astronomical Journal study.

At a distance of 250 million light years from Earth (very close in astronomical terms), the galaxies previously avoided detection due to dense clouds of dust in the Milky Way, lead author Professor Lister Staveley-Smith of the University of Western Australia branch of the International Centre for Radio Astronomy Research (ICRAR) explained.

“The dust clouds in the plane of our own Milky Way are so dense that not even large infrared and space telescopes can peer through them to see on the ‘other side’ of our galaxy,” Staveley-Smith told redOrbit via email. “Only a large radio telescope with a sensitive wide-field receiver can see these objects. Even then, it required many months of mapping the sky!”

He and a team of colleagues from the US, Australia, South Africa and the Netherlands outfitted the Parkes radio telescope at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) facility in New South Wales with the innovative receiver that allowed them to peer into the dust cloud and observe a previously unexplored part of the universe.

hidden galaxies

This is an annotated artist's impression showing radio waves traveling from the new galaxies, then passing through the Milky Way and arriving at the Parkes radio telescope on Earth (not to scale). (Credit: ICRAR)

Discovery could explain Milky Way’s movement, the Great Attractor

In all, Staveley-Smith’s team said they discovered 883 galaxies on the other side of the Milky Way dust cloud, one-third of which had never previously been seen. As Professor Renée Kraan-Korteweg, an astronomer at the University of Cape Town, explained, scientists have tried to map the distribution of galaxies behind the Milky Way for several decades.

“We've used a range of techniques but only radio observations have really succeeded in allowing us to see through the thickest foreground layer of dust and stars,” she said in a statement. “An average galaxy contains 100 billion stars, so finding hundreds of new galaxies hidden behind the Milky Way points to a lot of mass we didn't know about until now.”

The discovery could also provide new insight into the Great Attractor, an extremely massive and gravitationally strong region of intergalactic space which the researchers said seems to be pulling on several hundred thousand galaxies (including the Milky Way) with as much force as a million billion suns. It could also help explain the movement of the Milky Way itself.

“Knowledge of the positions and properties of the new galaxies allow us to better map the structure of the local Universe, and better assess what is responsible for the motion of the Milky Way and other nearby galaxies,” Staveley-Smith said. “It will also enable us to assess whether our knowledge of how the Universe evolves is correct. In the best cosmology model, gravitational acceleration is not predicted to arise from very distant structures. So finding the distance of the Great Attractor is very important.”

Currently, the study authors note that experts don’t fully understand what causes gravitational acceleration on the Milky Way, nor are they certain what the source of this acceleration is. But our galaxy is currently moving towards a few large clusters or superclusters of galaxy at speeds of more than two million kilometers per hour, and several new structures identified in this new study could help explain why.


This is an artist's impression of the galaxies found in the "Zone of Avoidance" behind the Milky Way. This scene has been created using the actual positional data of the new galaxies and randomly populating the region with galaxies of different sizes, types and colors. (Credit: ICRAR)