4 mins read 12 Oct 2021

Ancient galaxies found shrouded in cosmic gas and dust

Obscured from view by cosmic gas and dust, two previously undiscovered ancient galaxies have been found by an international team of astronomers.

Distant galaxies imaged with ALMA, the Hubble Space Telescope, and the European Southern Observatory’s VISTA telescope. Green and orange colors represent radiations from ionized carbon atoms and dust particles (observed by ALMA). Blue is the near-infrared radiation (observed with VISTA and Hubble). REBELS-12-2 and REBELS-29-2 were not detected in the near-infrared suggesting that these galaxies are deeply buried in dust. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, ESO, Fudamoto et al.

Two ancient galaxies formed less than 1 billion years after the Big Bang, have been discovered in what had appeared to be empty regions of space, cloaked by cosmic gas and dust.  

As part of an international research collaboration called REBELS (Reionization-Era Bright Emission Line Survey), which includes two core team members from Swinburne University, the astronomers were analysing two distant galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.  They noticed unexpected strong emissions at millimeter wavelengths near their intended targets that seemed to be coming from an empty area of space. 

To understand where the emissions were coming from, the team started a detailed analysis which showed they were in fact separate ancient galaxies brimming with stars, overlooked and obscured by giant clouds of cosmic gas and dust. The discovery suggests that many more galaxies may still remain hidden in the early Universe, far more than researchers expected.

So how did ALMA find the galaxies when even the sensitive Hubble Space Telescope saw nothing at all? 

Dr. Yoshinobu Fudamoto (Waseda University and the National Astronomical Observatory of Japan) was the one who initially noticed the unexpected emissions and is the lead author of the study published in the journal Nature.

“These new galaxies were missed not because they are extremely rare, but only because they are completely dust-obscured.”

The Hubble Space Telescope studies the universe at shorter visible wavelengths while ALMA uses faint millimeter-wavelength light emitted by cosmic gas and dust used in star formations. ALMA can directly detect the emission of dust and carbon atoms in the gas surrounding the galaxies. These galaxies are not visible in the UV or visible wavelengths as they are almost completely obscured by cosmic dust.  

One of them represents the most distant dust-obscured galaxy discovered so far. 

On the left is a view of the region that the Hubble Space Telescope shows as empty however ALMA revealed an undiscovered galaxy obscured by cosmic gas and dust. The views of the galaxies on the right are artist’s impressions of the galaxies. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope.

“Studying these early times, when the Universe was very young and galaxies had just started to form stars, is one of the ultimate frontiers in astronomy,” says co-author of the study, Swinburne’s Dr Themiya Nanayakkara.

“It is essential for our understanding of the formation of all stars and galaxies and ultimately tells the story of our own origins.” 

Co-author Prof. Ivo Labbé (Swinburne University of Technology) says to find such dust-enshrouded galaxies this early in time, less than 1 billion years after the Big Bang, was completely unexpected.

“Cosmic soot is produced in stars that act as factories. It’s a kind of cosmic air pollution, really,“ says Prof. Labbé.

“Over time you eventually can’t see the stars anymore due to the thick smog.”

Prof. Labbé is a leader in the study of distant universes and was part of the international team that holds the world record for discovering the most distant galaxy ever observed at 13.4 billion light-years away.

“So that’s looking 13.4 billion years into the past and the universe is 13.8 billion years old today. So, we’re only talking about a few hundred million years after the big bang,” he says.

This discovery suggests that many more galaxies might still be hidden and our picture of the beginning of the Universe is far from complete.

James Webb Space Telescope

View of the golden James Webb Space Telescope from overhead, with its secondary mirror booms stowed. JWST's mirrors are covered in a microscopically thin layer of gold, which optimizes them for reflecting infrared light, which is the primary wavelength of light this telescope will observe. Credit: NASA/Goddard/Chris Gunn.

The James Webb Space Telescope (also called JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope. It has a longer wavelength coverage and greatly improved sensitivity. The longer wavelengths enable Webb to look much closer to the beginning of time and to hunt for the unobserved formation of the first galaxies, as well as to look inside dust clouds where stars and planetary systems are forming. 

“Completing our census of early galaxies with the currently missing dust-obscured galaxies, like the ones we found this time, will be one of the main objectives of JWST and ALMA surveys in the near future,” says co-author Prof. Pascal Oesch from the University of Geneva.

Webb is due to launch on 18 December 2021, via an Arianespace Ariane 5 rocket from Europe’s Spaceport in Kourou, French Guiana, northeastern coast of South America. Live coverage will air on NASA TV.