It's puzzled scientists for decades: a region of space so obscured by the dust and gas at the core of the Milky Way galaxy that it's remained elusively impenetrable. This so-called Zone of Avoidance harbours a mystery. It's an anomaly known as the Great Attractor. The strong gravitational force, roughly 150 million to 250 million light-years away, appears to be coming from a mass up to tens of thousands of times that of the Milky Way galaxy. Even the Milky Way itself is being drawn in.
Scientists have been trying to get to the bottom of the Great Attractor since its discovery in the 1970s. Now, an Australian-led international team, seeing past all the dust and gas, might have discovered the answer. Their research has been published in the Astronomical Journal.
The team found 883 galaxies, a full third of which were new discoveries, using a special instrument -- a multibeam receiver -- outfitted to the Parkes radio telescope in Parkes, Australia. The Commonwealth Scientific and Industrial Research Organisation operates the dish.
"We don't actually understand what's causing this gravitational acceleration on the Milky Way or where it's coming from," said lead author Lister Staveley-Smith from The University of Western Australia node of the International Centre for Radio Astronomy Research.
"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 2 million kilometres per hour," Staveley-Smith said.
Astronomers were already aware of the Norma cluster, which can't on its own account for the strength of the gravitational force. The team, however, found three new clusters of galaxies in the galaxy wall filament that contains Norma. These have been named NW1, NW2 and NW3. The team also found two in the Centaurus Great Wall, which also borders the Zone of Avoidance, named CW1 and CW2.
Together, these clusters contain hundreds of new galaxies.
"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," said University of Cape Town astronomy professor Renée Kraan-Korteweg.
The newly discovered galaxies still don't entirely account for the Great Attractor's force, but they do indicate that there's a lot more to be discovered in the Zone of Avoidance. The team expects that more will be revealed in upcoming surveys using the Square Kilometre Array precursor telescopes.
"These surveys will together cover the whole sky and provide for the first time a deeper and well-resolved complete census of the large-scale structures in the sky, inclusive of the Milky Way," the study concludes.