The galaxy whose light has traveled nearly 13.5 billion years to reach us has been confirmed to be the oldest galaxy found to date.
By studying the galaxy’s oxygen content using the Atacama Large Millimeter/Subarray Array (ALMA), astronomers have precisely dated it to just 367 million years after the Big Bang, a time when the first lights in the universe were still on and beginning to spread freely through space. .
The result confirms observations made by the JWST, and provides new information about the early universe that tells us about the origins of the elements.
“The first images from the James Webb Space Telescope revealed so many early galaxies that we felt we had to test its results with the best observatory on Earth,” says astronomer Tom Bax of Nagoya University in Japan.
“It was a very exciting time to be an observational astronomer, and we could track the status of the observations that will test the JWST results in real time.”
The galaxy, named GHZ2/GLASS-z12, was first spotted by JWST in July of last year, shortly after the telescope opened its fragmented golden eye to the infrared light of the universe.
A research paper published in November details the discovery, dating the galaxy to roughly 350 million years after the Big Bang, which occurred about 13.8 billion years ago.
This is truly amazing, but any astronomical discovery is significantly more powerful if it can be confirmed with an independent instrument.
So a team led by Bax and astronomer Jorge Zavala of the National Astronomical Observatory of Japan turned to the ALMA radio telescope to learn more about the fledgling galaxy.
They switched ALMA to the direction of GHZ2/GLASS-z12 and began looking for an emission signature on the oxygen-related radio spectrum.
Because oxygen takes a relatively short time to form, it is commonly used to learn more about galaxies in the early universe. As the light enters the oxygen, it is re-emitted in a specific wavelength range, which results in a brighter line on that part of the spectrum.
Each of the 12- and 12-m radio antennas that make up the ALMA were turned on, eventually leading to the detection of an oxygen emission line near the position of GHZ2/GLASS-z12. Follow-up analyzes and statistical tests determined that the signal was real and related to the galaxy.
“We were initially concerned about the slight difference in position between the detected oxygen emission line and the galaxy Webb saw,” Buck explains.
“But we did detailed tests on the observations to confirm that this is a really strong detection, and it is very difficult to explain it through any other explanation.”
The very small distance between the galaxy and the oxygen emission could indicate that explosions or violent interactions stripped the galaxy of a great deal of its gas, causing it to fly into intergalactic space.
The team dated their observations to a more precise 367 million years after the Big Bang. Based on the brightness of the emission line, they were able to deduce that the galaxy formed large amounts of elements heavier than hydrogen and helium relatively quickly.
This is very interesting. The early universe, before stars appeared, was composed mostly of hydrogen with less helium. Then the stars formed. In their hot, dense cores, they began to smash atoms together, forming heavier elements.
But these elements were confined inside the stars. It wasn’t until stars died, exploding in spectacular supernovae, that heavier elements could spread through interstellar space.
This early presence of oxygen in the universe gives us some clues about the timing and evolution of these first stars, which we are not yet able to see directly.
“These deep ALMA observations provide strong evidence for the existence of galaxies during the first few hundred million years after the Big Bang, and confirm the surprising findings from Webb’s observations,” Zavala says.
“JWST’s work is just beginning, but we are already adjusting our models of how galaxies formed in the early universe to match these observations. The combined power of Webb and the ALMA radio telescope array gives us the confidence to push our cosmic horizons closer to the dawn of the universe.”
Research published in Monthly Notices of the Royal Astronomical Society.