Astronomers just found more than 70 'invisible' galaxies lurking in the deepest, darkest patch of the night sky

NASA/ESA/IPAC/Caltech/STScI/Arizona State UniversityNine years’ worth of observations by the Hubble Space Telescope revealed about 10,000 galaxies.
  • The Hubble Ultra Deep Field image is one of the most detailed photos of the darkest corners of the universe.
  • The image, built over more than a decade with hundreds of long exposures, has revealed 10,000 galaxies.
  • However, a large ground-based telescope recently found 72 galaxies that are invisible in Hubble’s best image.
  • The new images also reveal the chemical makeup of many galaxies and some of their strange, haloed structures.

Over the past two decades, the Hubble telescope has stared at a dim corner of the universe to create the Hubble Ultra Deep Field image, where astronomers have found about 10,000 galaxies hiding in the void.

But a new stare-down of this meticulously studied patch of night sky has added close to 100 previously undetected galaxies to the tally, among other amazing discoveries.

The patch astronomers looked at is less than 1% the size of the full moon, and it is one of the darkest regions in the night sky.

Hubble began photographing it consecutively in the mid-1990s, leading to the space-based observatory’s first deep-field images. They’re labelled “deep” because light has a finite speed yet the universe is expanding, so the farther away one sees an object, the deeper back in time it is. (Parts of the HUDF image show galaxies 13.2 billion years ago – just a few hundred million years after the Big Bang.)

Imaging techniques improved Hubble’s photo resolution, and the installation of a new camera in 2009 spurred NASA, the ESA, the Space Telescope Science Institute, and other collaborators to perform a new staring contest. Hundreds of new photos, including those in near-infrared and ultraviolet, were combined to create the latest deep-field image that NASA released in 2014.

Yet from 2014 to 2016, a group of astronomers used the Very Large Telescope in the mountains of Chile to study the location anew. In particular, they used a telescope instrument called MUSE – short for Multi Unit Spectroscopic Explorer – to photograph it for a total of 137 hours.

“MUSE can do something that Hubble can’t – it splits up the light from every point in the image into its component colours to create a spectrum,” Roland Bacon, a researcher at the Lyon Astrophysics Research Center in France, said in a press release. “This allows us to measure the distance, colours and other properties of all the galaxies we can see – including some that are invisible to Hubble itself.”

MUSE’s new look at Hubble’s famous patch of night sky led to the publication of 10 new studies in the journal Astronomy & Astrophysics on Wednesday.

Some of the studies describe the techniques used, but others reveal 72 previously undetected galaxies, which were each about 100 times fainter than those found in other surveys. The new batch of research also details the chemical make-up of very young galaxies, some of which had strange halos of gas – findings that will help cosmologists better understand how the universe evolved over billions of years.

More deep-field discoveries are almost certainly on the way. Astronomers have only examined a sixth of the galaxies in the HUDF region, and MUSE received a major, laser-powered upgrade in August.

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