Astronomers have just confirmed the oldest galaxies ever observed

When a bunch of photons hit the near-flawless mirrors of the James Webb Space Telescope earlier this year, they had been traveling through the void for 13.4 billion years. The light was emitted from distant galaxies at a time when the birth of everything we know and see was still, in a cosmic sense, recent history. Ancient doesn’t really do it justice.

Webb’s first deep-field images: infrared recordings of tiny patches of sky, full of galaxies.caused a revolt among astronomers to find the oldest galaxies in sight. The Hubble Space Telescope held the existing record with observations of a galaxy from when the universe was only 400 million years old. Webb’s larger mirrors and the ability to see the infrared parts of the spectrum were designed to do this better.

On Friday, the telescope proved its worth when a team of scientists, collectively known as JADES, a collaboration between the builders of two of Webb’s instruments, NIRcam and NIRspec, announced that they had confirmed observations of the oldest galaxies Bye now.

“For the first time, we have discovered galaxies just 350 million years after the Big Bang, and we can be absolutely sure of their fantastic distances.” said Brant Robertson of the University of California Santa Cruz, a member of the NIRCam science team and co-author of a recent paper on the work.

Astronomers began compiling a list of candidates by analyzing data from Webb’s NIRcam instrument, an exquisitely sensitive infrared camera. Almost immediately after the first Webb images became public, stories of extremely old galaxies hit the web.

But while the NIRcam observations revealed a rich population of targets worthy of a closer look, official confirmation required detailed spectroscopic analysis.

“It is quite possible that the nearest galaxies are masquerading as very distant galaxies,” said astronomer and co-author Emma Curtis-Lake of the University of Hertfordshire in the United Kingdom.

Thanks to NIRspec, in two recent studies (here i here), the teams were able to conduct spectroscopic analyses, the gold standard for confirming the distance and age of these incredibly faint early galaxies, for a number of candidates. Although neither study has yet been peer-reviewed, the findings likely beat Hubble’s record.

Renske Smit of Liverpool John Moores University, the patch of sky observed is about the size of the Queen’s eye “on a pound coin held at arm’s length”. said the BBC. Within this eye are nearly 100,000 galaxies, each captured at a time billions of years ago.

To measure the age of a galaxy near the beginning of the universe, scientists measure its “redshift.” As light travels, the expansion of the universe lengthens its wavelength, docking it in the redder parts of the spectrum. Some of the oldest light has stretched out of the visible spectrum and into the infrared, Webb’s specialty.

Older galaxies are not only visible in the infrared, but their spectrum is also cut off at a specific point due to the scattering of intergalactic hydrogen. Faint infrared galaxies exhibiting this cutoff, moving at higher redshift, filled out a group of candidates. The team then spent 28 hours observing 250 of these with NIRspec. This detailed spectroscopic analysis included specific atomic signatures and pinpointed the redshift.

Four galaxies turned out to be exceptionally old, with redshifts greater than 10. Two showed redshifts at 13 years, from a time when the universe was only 330 million years old. The team says these galaxies are small, only a hundred million solar masses, and made up of young stars less than 100 million years old. By comparison, the Milky Way is thought to have at least 100 billion stars and the Sun is about 4.6 billion years old. Despite their small size, the team says these early galaxies produced stars at a prodigious rate, up to 10 times faster than the closest galaxies of similar size today.

These galaxies now appear to hold the record for the oldest spectroscopically confirmed, but the title may not last long. Although they are still awaiting confirmation, scientists have estimated that some galaxies already captured by Webb are even older, and Webb was designed to see light from times as early as 100 million years after the Big Bang.

By studying the first stars and galaxies, scientists I hope to learn more on the formation of galaxies and to determine a period in the evolution of the universe known as reionization, when the strong light from the first stars ionized the surrounding gas by removing electrons from hydrogen and helium. Since the stars in these four galaxies may have started forming up to 100 million years earlier, this first generation of stars can be dated to about 230 million years after the Big Bang.

“With these measurements, we can learn the intrinsic brightness of galaxies and find out how many stars they have,” Robertson said. “Now we can start to really pick out how galaxies combine over time.”

Image Credit: NASA, ESA, CSA and STScI