Observations of the oldest galaxies ever discovered by the James Webb Space Telescope have been confirmed, scientists have announced. Stephen Charlotte, a researcher at the Paris Institute of Astrophysics and co-author of the discovery, explains.
The four galaxies described in the works published before you online were revealed last Friday NASA And thisESA ?
Stephen Charlotte : Named JADES-GS-z13-0 and 33 billion light-years away (1 light year = 9.461 x 1012 KM, Editor’s note), the oldest of these early galaxies was 300 million years after the Big Bang, when the Universe was only 2% of its current age. The other three (JADES-GS-z12-0, -z11-0 and -z10-0), spread after a hundred million years. By comparison, the oldest known galaxy so far, GN-z11, discovered by the Hubble Space Telescope in 2016, dates back 400 million years after the Big Bang. Our work defines a new frontier in the study of galaxy formation!
Why is it important to find ancient galaxies?
CS To understand the most distant period in the history of the primitive universe: the “cosmic dawn”, when the universe emerged from darkness illuminated by the brightness of the first stars. To date, we know that after the Big Bang, about 13.7 billion years ago, the expanding universe cooled and experienced a long period of darkness. Then about 100 million years later, as a result of gravity, the material would have condensed in some places and formed the first stars in the formation of the first galaxies. But exactly under what physical conditions did these first stars form? How did they assemble into galaxies? When and for how long did their intense radiation ionize the universe’s atoms, triggering “reionization,” another important period in the early universe? Observing the first objects that lit up the universe—the holy grail of cosmology—will help solve these puzzles. Hence, trace the history of the first moments of the universe and, therefore, the origin of our world.
The JWST Advanced Deep Extragalactic Survey (JADES) focuses on and around the Hubble Space Telescope’s extreme deep field and precisely measures the redshift (z) of each galaxy.
How did you find the above four constellations?
CS Thanks to the exploitation of the first images taken by the US James Webb Space Telescope from July 2022. Developed by the US space agency NASA in collaboration with the European (ESA) and Canadian (CSA) space agencies and launched in December 2021 by an Ariane rocket from Courou (French Guiana), the device is specially designed to detect the light of the first stars in the universe. Let us mention here that light reaching us from a very distant star sends back the image it had when it emitted this light, which sometimes takes billions of years to reach us. Due to the expansion of the universe, this light is stretched into the longer and redder wavelengths of the light spectrum; This is called the “red shift”. Also, the light of the first stars and galaxies has become much redder. Consequently, to detect it, you need a telescope capable of seeing in the infrared… This is precisely the case with James Webb, which, unlike its predecessor, the Hubble Space Telescope (which focused on visible light), specialized in infrared observations. .
But James Webb had already published galaxies as old as you describe them, right?
SC Not exactly… It’s true that in the summer of 2022, several groups, including ours at the Paris Institute of Astrophysics, analyzed James Webb’s first images and reported finding galaxies there. Almost 250 million years after the Big Bang. But, more importantly, these are only “candidate possible ancient galaxies” and hence hypotheses. Their seniority relative to the Big Bang was confirmed by direct measurements of their redshifts. The Jades collaboration is now complete!
A view of part of the Large Magellanic Cloud, a satellite region of the Milky Way, by the James Webb Telescope’s NIRSpec spectrograph and NIRCam camera.
What is this jades collaboration?
CS A consortium of more than eighty astronomers from ten countries (of which I am the only French), began meeting in 2015 to propose an ambitious project of the same name. It aims to provide an unprecedented view of the early universe in terms of depth and detail. To do this, he was allocated more than a month of the telescope’s observation time over two years. Subsequently, Jades scientists spearheaded the development of two of the four most powerful instruments aboard the James Webb.
What are these two tools?
CS NIRCam (Near Infrared Camera), an infrared camera built by the University of Arizona and US defense and security company Lockheed Martin, is capable of capturing the heat emitted by a bumblebee at a distance of nearly 400,000 km. and the infrared spectrometer NIRSpec (“near infrared spectrometer”) developed by ESA and Airbus and is capable of collecting the light spectra of about 250 galaxies simultaneously. It was these two instruments that were able to confirm the ages of the four galaxies in question here.
Sure, how did you proceed?
CS Using NIRCam, we observed a small patch of sky in and around a region called “Hubble’s ultra-deep field” for ten days, in nine different infrared wavelength ranges. and 2004 by the Hubble Space Telescope. Although this area is very small (Human size as seen from a distance of 1.6 km, NASA, editor’s note), the NIRCam data found nearly 100,000 galaxies there. Of these, we selected those that were not very bright at the longest infrared wavelengths and were completely invisible below the critical wavelength; A distinctive feature of galaxies in the early universe. We used the NIRSpec instrument to precisely measure the redshift of each galaxy. This is where we found that some of the galaxies studied date back less than 400 million years to the Big Bang.
The JWST NIRSpec spectrograph is the European instrument behind this confirmation.
Your data made it possible to describe – a little – these galaxies…
CS Yes. Measurements by the NIRCam camera show that these cosmic structures are about one percent the size of our galaxy, the Milky Way, and as bright. The modeling application led to the conclusion that each of them already contains a hundred million solar-mass stars. According to NIRSpec measurements, they suggest that these galaxies are about a hundred times less enriched in metals (elements heavier than helium, forged by stars) than the Milky Way; Another sign that they are only at the beginning of their evolution.
What does this information show about the beginning of the universe?
CS Taken together, they say that the first generations of galaxies formed faster than we thought!
Hubble’s Deepest Field photograph observed between September 24, 2003 and January 16, 2004.
About your next tracking campaigns?
CS Our Jades project will continue in 2023 with a search for other ancient galaxies in another part of the sky: Hubble’s iconic Deep Field, photographed in 1995 and located in the Ursa Major galaxy. We will observe it again at the end of 2023, when the region of the celestial vault on which our recent work focused is once again visible in the sky. In fact, NIRCam observations indicate the existence of galaxies that are even older than what is now confirmed. But this requires confirmation by spectroscopic measurements.
What are your hopes for the future?
CS I hope to be able to go back as far as possible in the history of the first moments of the universe; In theory, James Webb could observe objects that appeared 100 million years after the Big Bang. If we succeed in this challenge, we will make discoveries that will forever challenge what we know so far about the formation of stars and galaxies in the first moments of the universe. ♦