Unknown galaxies discovered lurking behind the Milky Way
In recent radio telescope studies, many hundreds of previously undiscovered galaxies have been found to exist in an area in which an enormous magnetic abnormality known as the "Great Attractor" is located. The new research may help shed light on why our galaxy, along with hundreds of thousands of others, is being inextricably pulled in that direction.
Using an advanced multibeam receiver on the CSIRO Parkes radio telescope in Australia (the instrument recently used as part of the search for extraterrestrial intelligence), researchers from Australia, South Africa, the US and the Netherlands were able to penetrate the stars and dust of the Milky Way that blocked the direct view of the other side of the galaxy, and peer into a region of which very little is known. In so doing, the team identified some 883 galaxies, where around one third had never been previously identified.
"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," said Professor Lister Staveley-Smith, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR).
The discovery may help to explain the Great Attractor region, which appears to be drawing the Milky Way and other galaxies towards it with a gravitational force equivalent to a million billion Suns. Sited at a relatively close distance to Earth in astronomical terms, and known as "The Zone of Avoidance" due to its hidden nature, the area is around 250 million light years away. According to Professor Staveley-Smith, the Great Attractor has been a constant source of speculation and research from the time when extreme aberrations in expected universal expansion were discovered in the area almost 50 years ago.
"We don't actually understand what's causing this gravitational acceleration on the Milky Way or where it's coming from," he said. "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."
Another astronomer participating in the study, Prof. Renée Kraan-Korteweg of the University of Cape Town concurred that researchers have been attempting to chart the galaxies suspected of being obscured behind the Milky Way for many years now.
"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," said Professor Kraan-Korteweg. "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 Great Attractor – also known as the Norma Cluster – has a mass equivalent to that of thousands of galaxies and, whilst it is huge, its size still doesn't fully account for the enormous pull being measured. It seems that the Great Attractor and galaxies surrounding it (including our own) are hurtling toward something even bigger. Dubbed the Shapley Supercluster, this conglomeration of more than 8,000 galaxies has an incredible mass of more than ten million billion of our suns, and every galaxy in our region of the Universe is heading toward it.
Of the many newly-identified structures revealed by the research, three new galaxy concentrations (NW1, NW2, and NW3) and two new clusters (CW1 and CW2, one of which forms part of the striking 180° long filament that dominates the southern sky), may be key in helping explain the movement of the Milky Way and other galaxies towards the Great Attractor region.
Much of this research has been made possible with the use of new technology being fitted to radio astronomical devices such as the Parkes Radio Telescope that, according to researchers, is enabling much faster surveying and recording of large swathes of the heavens. As a result, more details of areas such as that of the Zone of Avoidance may be more quickly gleaned, and further light shed on the reasons so many galaxies are being attracted to it.
"With the 21-cm multibeam receiver on Parkes we're able to map the sky 13 times faster than we could before and make new discoveries at a much greater rate," said Dr. Bärbel Koribalski of CSIRO Astronomy and Space Science.
The findings were recently published in the Astronomical Journal.