New and detailed atlas of the skies

A new radio telescope in outback Western Australia has just created an atlas of the southern sky in record-breaking time, demonstrating that detailed all-sky surveys can now be done in weeks instead of years.

Over just 300 hours, CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP) mapped three million galaxies, one million of which we’d never seen before.

The survey covered 83% of the entire sky by stitching together 903 individual wide-field images – an impressive feat considering that existing survey telescopes need tens of thousands of images to achieve the same coverage. 

RACS is also twice as sensitive as previous comparable surveys. Each image contains 2000-4000 objects – mostly distant radio-bright galaxies, but also objects within the Milky Way like supernova remnants and pulsars.

The initial results of the survey, called the Rapid ASKAP Continuum Survey (RACS), are published in the journal Publications of the Astronomical Society of Australia. 

“For the first time, ASKAP has flexed its full muscles, building a map of the Universe in greater detail than ever before, and at record speed,” says lead author and CSIRO astronomer David McConnell. “We expect to find tens of millions of new galaxies in future surveys.”

Such broad snapshots of the sky will help astronomers statistically analyse huge populations of galaxies and thus answer questions about their origins, dynamics and evolution.

“This census of the Universe will be used by astronomers around the world to explore the unknown and study everything from star formation to how galaxies and their supermassive black holes evolve and interact,” McConnell says.

ASKAP’s key feature is its wide field of view, allowing it to take detailed panoramic images. Most radio receivers can only see a small part of the sky, so performing large-scale surveys is time-consuming. But by increasing the number of receivers and spacing them over a large area, radio telescopes can stitch together dozens of signals and therefore “see” a larger patch of sky. 

ASKAP comprises 36 antennas spread over of six kilometres in a remote, radio-quiet area. These antennas feed massive amounts of data to a supercomputing facility 700 kilometres away in Perth, which then reconstructs the images. 

With many receivers working as one, the telescope has a 30-square-degree view of the sky – about as large as the Southern Cross, and about 40 times larger than the area viewed by a traditional radio telescope.

This survey, RACS, will likely replace major existing all-sky surveys as a first reference point for astronomers, providing a baseline comparison for future studies to refer back to and determine what has changed.

But this this survey was just a test. ASKAP’s main scientific program will launch in 2021, performing several more in-depth surveys over five years. 

“Future ASKAP work, the surveys for which the telescope was designed, will take longer and see more deeply into the universe,” says McConnell.

These results will also be used to design projects for the Square Kilometre Array (SKA) – a massive, continent-spanning astronomy project that will become the world’s biggest radio telescope. Its low-frequency node will be hosted by the Murchison Radio-astronomy Observatory, where ASKAP is currently picking up whisper-quiet radio signals from the distant universe.