Milky Way by Matt Dieterich

Great Attractor Revealed? Galaxies Found Lurking Behind the Milky Way

Article Updated: 18 Mar , 2016

Hundreds of galaxies hidden from sight by our own Milky Way galaxy have been studied for the first time. Though only 250 million light years away—which isn’t that far for galaxies—they have been obscured by the gas and dust of the Milky Way. These galaxies may be a tantalizing clue to the nature of The Great Attractor.

On February 9th, an international team of scientists published a paper detailing the results of their study of these galaxies using the Commonwealth Scientific and Industrial Research Organization’s (CSIRO) Parkes radio telescope, a 64 meter telescope in Australia. The ‘scope is equipped with an innovative new multi-beam receiver, which made it possible to peer through the Milky Way into the galaxies behind it.

The area around the Milky Way that is obscured to us is called the Zone of Avoidance (ZOA). This study focused on the southern portion of the ZOA, since the telescope is in Australia. (The northern portion of the ZOA is currently being studied by the Arecibo radio telescope, also equipped with the new multi-beam receiver.) The significance of their work is not that they found hundreds of new galaxies. There was no reason to suspect that galactic distribution would be any different in the ZOA than anywhere else. What’s significant is what it will tell us about The Great Attractor.

The Great Attractor is a feature of the large-scale structure of the Universe. It is drawing our Milky Way galaxy, and hundreds of thousands of other galaxies, towards it with the gravitational force of a million billion suns. The Great Attractor is an anomaly, because it deviates from our understanding of the universal expansion of the universe. “We don’t actually understand what’s causing this gravitational acceleration on the Milky Way or where it’s coming from,” said Professor Lister Staveley-Smith of The University of Western Australia, the lead author of the study.

“We know that in this region there are a few very large collections of galaxies we call clusters or superclusters, and our whole Milky Way is moving towards them at more than two million kilometres per hour.”

The core of the Milky Way seen in Infrared. Seeing through this has been a real challenge. Credit: NASA/Spitzer

The core of the Milky Way seen in Infrared. Seeing through this has been a real challenge. Credit: NASA/Spitzer

Professor Staveley-Smith and his team reported that they found 883 galaxies, of which over one third have never been seen before. “The Milky Way is very beautiful of course and it’s very interesting to study our own galaxy but it completely blocks out the view of the more distant galaxies behind it,” he said.

The team identified new structures in the ZOA that could help explain the movement of The Milky Way, and other galaxies, towards The Great Attractor, at speeds of up to 200 million kilometres per hour. These include three galaxy concentrations, named NW1, NW2, and NW3, and two new clusters, named CW1 and CW2.

University of Cape Town astronomer Professor Renée Kraan-Korteweg, a member of the team who did this work, says “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.”

How exactly these new galaxies affect The Great Attractor will have to wait for further quantitative analysis in a future study, according to the paper. The data from the Arecibo scope will show us the northern hemisphere of the ZOA, which will also help build our understanding. But for now, just knowing that there are hundreds of new galaxies in our region of space sheds some light on the large-scale structure of our neighbourhood in the universe.


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