Australian astroboffins reveal hundreds of hidden galaxies

Parkes telescope finds a million, billion suns behind the Milky Way

ICRAR visualisation of the hidden galaxies
Behind the Milky Way: ICRAR's visualisation of the "hidden galaxies"

Data collected by Australia's Parkes radio telescope from as far back as 1997 has led astronomers to declare they've discovered hundreds of galaxies hidden from telescopes by the Milky Way.

The result is exciting for astro-boffins, because the mass of the 300 newly-spotted galaxies, plus new and better information about 500 known galaxies, helps to explain what's called “The Great Attractor”.

The Great Attractor is a region that's drawing hundreds of thousands of galaxies – including our own – towards it “with a gravitational force equivalent to a million billion Suns”, says the International Centre for Radio Astronomy Research (ICRAR).

Astronomers have been interested in the attractor since the 1970s, when they first noticed that some galaxies weren't following the universal expansion of the rest of the universe.

Professor Lister Staveley-Smith (University of Western Australia) says “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”.

Smithsonian Magazine notes that the massive Norma Cluster anchors the region with thousands of galaxies: “But even that isn't massive enough to account for the Great Attractor's incredible pull”.

With two new galaxy clusters and three “galaxy concentrations” identified by the study, at least some of the Attractor's gravity can now be accounted for.

As collaborator Professor Renée Kraan-Korteweg from the University of Capetown put it: “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 21 cm wavelength receiver on the Parkes telescope, HIPASS, looks for H1 hydrogen (one proton, one electron), the most common isotope of the universal building block. Most of its data was collected between 1997 and 2002.

Professor Staveley-Smith told The Register today that finding and confirming the presence of these galaxies has needed years of analysis.

At the time HIPASS was collecting data, astronomers used the 21 cm multibeam receiver to run a “much deeper survey in a smaller region of the sky, because the Zone of Avoidance (the 'blind spot' caused by the Milky Way – El Reg) is so special”.

That separate survey went around 2.5 times deeper than HIPASS, to “take us to the mean redshift of the Great Attractor”.

“We've been analysing that data continuously since the observations,” he added.

The search for hidden galaxies is far from over. Australia's WALLABY – Widefield ASKAP L-band Legacy All-Sky Blind Survey – is on the hunt for half a million galaxies. ®

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