Astrophysicist Renske Smit reacts to seeing 'furthest corner of known Universe'.

The most distant corners of the Universe have been seen by human eyes for the first time, scientists have confirmed. 

The farthest galaxies from Earth – 13.4 billion light years away – were discerned in images taken by NASA’s James Webb Space Telescope - the most powerful telescope ever launched.

Earlier data from Webb had provided candidates for such infant galaxies and these have now been confirmed by scientists in the US and Europe using long spectroscopic observations.

Two papers in Nature, published this week, revealing the characteristic and distinctive patterns in the rainbows of light coming from these incredibly faint galaxies.

“The light we are measuring with has been travelling 13.4 billion years to get to us – an astonishing distance that makes even the most seasoned astronomer’s mind boggle,” said Dr Renske Smit, a researcher from Liverpool John Moores University’s Astrophysics Research Institute.

“That light emanates from a moment when the Universe was just 2% of its current age, the very infancy of the Universe!”

Dr Smit is part of a large team, including the universities of Hertfordshire and Cambridge, who have been analysing data from instruments onboard JWST, the Near-Infrared Camera (University of Arizona/Lockheed Martin) and ESA’s Near-Infrared Spectrograph. 

Together they run the Advanced Deep Extragalactic Survey (JADES) to provide a view of the early Universe unprecedented in both depth and detail.

The first round of JADES observations have focused on the area in and around the Hubble Ultra Deep Field.  For over 20 years, this small patch of sky has been the target of nearly all large telescopes, building an exceptionally sensitive data set spanning the full electromagnetic spectrum.  Now JWST is adding its unique view, providing the faintest and sharpest images yet obtained.

One image, although only the angular size of a human viewed from a mile away, the image teems with nearly 100,000 galaxies, each caught at some moment in their history, billions of years in the past.

For Renske and her colleagues, it is beyond exciting. She says: “It was my responsibility to lead the first data analysis, obtaining the first detailed distance measurements using LJMU’s high performance computing facility, Prospero.

“This analysis rejected some of the less robust galaxy candidates as ‘interlopers’, but confirmed others as, indeed, being the most distant sources ever seen and confirmed.

“There was a moment where I was looking at my screen at the results, being very much aware and thrilled that I was one of the first people to ever see these sources at the very edge of the Universe.”

Colleague Brant Robertson from University of California Santa Cruz, a member of the Near-Infrared Camera science team, echoed this: "The images from this telescope are breathtaking.  One sees the full span of galactic history: distant young galaxies and nearby more mature ones.  And JWST reveals such a beautiful complexity of each,” he said.

The team were able to age the galaxies by searching for faint galaxies that are visible in the infrared but whose spectra abruptly cut off at some critical wavelength. Those from the early Universe can be distinguished by a tell-tale aspect of their multi-band colours.  Ultraviolet light with wavelengths shorter than 121 nanometers travels very poorly through intergalactic space; it is scattered by the omnipresent fog of hydrogen atoms and doesn't reach us. 

But light is stretched in wavelength as the Universe expands and the light from these youngest galaxies has been stretched by a factor of up to 14, so that the threshold for the light to survive to reach us has shifted out to 1.7 microns. 

Additionally, the team collected the light from 250 faint galaxies and spreads the light into a rainbow – using the Near Spectrograph, separating hundreds of distinct wavelengths in each galaxy.  From this, astronomers can see the characteristic patterns from the atoms in each spectrum, allowing a precise measurement of the redshift and revealing the properties of the gas and stars in the galaxy.

"These are by far the faintest infrared spectra ever taken.”, says astronomer Stefano Carniani from Scuola Normale Superiore in Italy.  “And they reveal what we hoped to see: a precise measurement of the cutoff wavelength of light due to the scattering of intergalactic hydrogen."

Four of the galaxies are particularly special, revealed to be at an unprecedentedly early epoch: these are extremely faint because of their great distance from us and because the stretching of the wavelength of their light by expansion of the universe, but scientists can now explore their properties, owing to the acute sensitivity of JWST.

Astronomer Sandro Tacchella from University of Cambridge, said the findings opened the door on new understanding: "It is hard to understand galaxies without understanding the initial periods of their development.  Much as with humans, so much of what happens later depends on the impact of these early generations of stars.  So many questions in about galaxies have been waiting for the transformative opportunity of JWST.”

So could we find even older, more distant galaxies and stars?

The likelihood is yes, given the team have two more years of data collection from James Webb.  “One of the most exciting results from this discovery is how bright some of these early galaxies already are. This could suggest that these galaxies are forming very rapidly but in essence, it means that we are just scratching the surface of the discoveries that JWST has to offer and we will be hunting galaxies even more distant than the ones we have seen here,” added Dr Smit.

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