Hundreds of hidden galaxies spotted behind the Milky Way


On a clear night, our own galaxy is a brilliant streak of stars across the sky. But it’s a right pain for astronomers trying to explore what lies beyond – until now. Belinda Smith reports.


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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.
ICRAR

Our galaxy is hurtling through space at two million kilometres per hour, inexorably drawn to a mysterious region with a gravitational force equivalent to a million billion Suns.

The problem is astronomers’ telescopes can’t see this so-called “Great Attractor” as the Milky Way is blocking the view. And they can’t shove the stars and dust aside, nor wait the hundreds of millions of years for our part of the spiral galaxy to swing round to the other side.

So astronomers led by the University of Western Australia’s Lister Staveley-Smith used a special receiver on the Parkes radio telescope to filter out foreground stars and dust.

They spotted 883 galaxies, a third of which had never been seen before – and may help explain the Great Attractor dragging us, along with hundreds of thousands of other galaxies, towards it.

"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," Staveley-Smith said.

"We don't actually understand what's causing this gravitational acceleration on the Milky Way or where it's coming from"

Astrophysicists have been trying to get to the bottom of the Great Attractor since hints of its existence cropped up in the 1970s, when they saw the motion of galaxies across hundreds of millions of light-years seemed to be moving towards one region – not expanding like they should.

"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."

The work, which involved taking hundreds of radiowave snapshots of each patch of Milky-Way-obscured sky over the course of three years to filter out foreground dust and stars, identified three galaxy concentrations (named NW1, NW2 and NW3) and two new clusters (named CW1 and CW2).

These may help explain our galaxy's movement.

"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," says University of Cape Town astronomer Renée Kraan-Korteweg, who was also involved with the study.

The work was published in the Astronomical Journal.

  1. http://iopscience.iop.org/article/10.3847/0004-6256/151/3/52
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