Astronomers have created the largest ever 3D map of 1 million distant galaxies otherwise obscured by the Milky Way’s neighboring dwarf galaxies, the Magellanic Clouds.
The Magellanic Clouds are irregularly shaped galaxies which are a stunning feature of the Southern Hemisphere sky visible to the naked eye. But the brightness of these dwarf galaxies, combined with the fact that they occupy a large area of the night sky, means that Milky Wayour neighbors block our view of many, many more distant galaxies. So when astronomers observe the billions of galaxies in the universethey tend to avoid that part of the sky.
“The Magellanic Clouds are beautiful galactic companions, but they unfortunately block some of our view of objects further away,” Keele University astronomer and map team member Jessica Craig said in declaration (opens in new tab). “Our work helps overcome this and in the process helps fill in the gaps in our map of the universe.”
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Craig and her colleagues tackled this problem by photographing the Magellanic Clouds at such high resolution that they could see through the gaps between stars that make up these galaxies. To make these images, the team turned to the Visible and Infrared Telescope for Astronomy (VISTA), based at the Paranal Observatory in Chile.
But these increasingly distant “hidden” galaxies are particularly difficult to see because they appear fainter and redder than they are due to the dust in the Magellanic Clouds. To account for this effect, the team turned to a radio telescope, the Galactic Australian Square Kilometer Array Pathfinder Survey (GASKAP), which can peer through the dust between Earth and distant galaxies. The GASKAP data allowed the scientists to create a detailed map of the gas and dust in the Magellanic Clouds and thereby account for the degree of “reddening” that these factors cause the galaxies they obscure.
The Small Magellanic Cloud obscures galaxies in the southern hemisphere. (Image: ESA/Hubble and Digitized Sky Survey 2)
Due to the large number of light sources in images of the Magellanic Clouds, the human eye alone cannot distinguish distant galaxies from closer objects. But stars shift in position while distant galaxies stay in the same place, so the team was able to use star mapping data Gaia Observatory to correctly categorize each light source.
Astronomers used a second technique to confirm the distinction between distant galaxies and relatively nearby stars. As the universe expands, as distant galaxies move away from Earth, the wavelength of light from those galaxies is stretched. The longer wavelengths of visible light are red, so astronomers call this elongation redshift.
The more distant an object is, the faster it is moving away and therefore the redder its light appears, so distant galaxies are redder than stars. By taking color into account, the team can further eliminate stars from their data.
Finally, the astronomers applied machine learning and artificial intelligence to line up the galaxies and create a 3D map of about 1 million galaxies.
Craig presented the team’s findings in mid-July at the National Astronomy Meeting held at the University of Warwick in the United Kingdom
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