We can observe nearby regions of the Milky Way and find orgies of star birth. The closest region is in the Orion nebula, where astronomers have identified more than 700 young stars. They range from just 100,000 years, from mere childhood for a start, to over a million years.

But we are now more than 13 billion years after the Big Bang. What was star formation like when, when conditions in the Universe were so different?

The JWST was conceived, designed and launched to answer questions about the early Universe. The JWST Advanced Deep Extragalactic Survey (JADES) program is a deep-field spectroscopic and imaging survey of galaxies from about z~12 to z~2, about 370 million to 3.3 billion years after the Big Bang. Its goal is to understand the formation and evolution of those galaxies and their stars in the early days of the Universe, one of the big questions of astronomy.

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“Previously, the first galaxies we could see just looked like small specks. Yet those spots represent millions or even billions of stars at the beginning of the universe.

Kevin Hainline, University of Arizona at Tucson

JADES is revisiting a region of the sky familiar to astronomy enthusiasts: the Hubble Ultra Deep Field (HUDF). Space telescope to capture. It contains about 10,000 galaxies, and the smallest and reddest date back to when the Universe was only about 800 million years old.

The JADES program uses two of the JWST’s tools together: NIRSpec (Near-Infrared Spectrograph) and NIRCam (Near-Infrared Camera) to revisit the region in and around the HUDF in greater depth and detail. The effort required 770 hours of observation. The JADES team has already identified hundreds of galaxies from when the Universe was less than 600 million years old. Some of them are alive with multitudes of hot, young stars.

Marcia Rieke of the University of Arizona in Tucson is the co-chair of the JADES program. “With JADES, we want to answer many questions, such as: how did the first galaxies assemble? How fast did stars form? Why do some galaxies stop forming stars? Rieke said.

The background to these questions is the Epoch of Reionization of the Universe (EOR).

EOR occurred within a billion years after the Big Bang. Before it, the Universe was filled with neutral hydrogen, an opaque gas that was impervious to light for hundreds of millions of years. Only when stars formed and reionized hydrogen did the Universe become transparent.

This diagram of the evolution of the universe from the big bang to the present shows the epoch of reionization.  Credit: NASA, ESA and A. Feild (STScI)
This diagram of the evolution of the universe from the big bang to the present shows the epoch of reionization. Credit: NASA, ESA and A. Feild (STScI)

Part of JADES focuses on galaxies that existed 500 to 850 million years after the Big Bang and during EOR. Ryan Endsley of the University of Texas at Austin led the investigation. Endsley and his colleagues used JWST’s NIRSpec instrument to look for signs of star formation in those galaxies. They found it in abundance.

“Nearly every single galaxy we’re finding shows these unusually strong emission line signatures that indicate intense recent star formation. These early galaxies were very good at making hot, massive stars,” Endsley said.

Massive stars burn hot and emit powerful UV radiation. The radiation ionized the hydrogen atoms, removing the electron and leading to EOR. The Universe is now composed mostly of low-density ionized hydrogen and remains transparent and open to observation with our telescopes. Because the earliest galaxies in the Universe contained large numbers of hot, massive stars, they likely drove the reionization process.

The JADES team has created an interactive tool to explore images of the JWST.  Lose yourself as you observe some of the first galaxies ever to form in the Universe.  Image Credit: JADES
The JADES team has created an interactive tool to explore images of the JWST. Lose yourself as you observe some of the first galaxies ever to form in the Universe. Image Credit: JADES

Endsley also discovered that these galaxies had periods of intense star formation and periods of weak star formation. Star formation could have increased dramatically as galaxies consumed clouds of star-forming gas. And the periods of depressed star formation may have been the result of massive stars themselves. Massive stars quickly burn up their fuel and explode as supernovae, which can inject energy into the surrounding gas, heating it up and preventing it from condensing and forming new stars.

To understand the early Universe, astronomers must observe it. This is the JWST’s forte. Part of JADES focuses on galaxies that existed when the Universe was less than 400 million years old. These galaxies may help answer the question of how different star formation was then than it is today. The light from those galaxies is redshifted due to the expansion of the Universe, and astronomers measure the redshift to know a galaxy’s age and distance. A redshift of 8 indicates that a galaxy existed when the Universe was less than 650 million years old, only about a couple hundred million years after the first stars and galaxies formed.

This slide from an AAS presentation highlights the JWST Advanced Deep Extragalactic Survey (JADES) study region.  This area is in and around the Ultra Deep Field of the Hubble Space Telescope.  JWST images are both bigger and deeper.  The scientists used Webb's NIRCam instrument to observe the field in nine different infrared wavelength ranges.  From these images, the team looked for faint galaxies that are visible in the infrared but whose spectra break off abruptly at a critical wavelength.  Image Credit: Kevin Hainline/JADES
This slide from an AAS presentation highlights the JWST Advanced Deep Extragalactic Survey (JADES) study region. This area is in and around the Ultra Deep Field of the Hubble Space Telescope. JWST images are both bigger and deeper. The scientists used Webb’s NIRCam instrument to observe the field in nine different infrared wavelength ranges. From these images, the team looked for faint galaxies that are visible in the infrared but whose spectra break off abruptly at a critical wavelength. Image Credit: Kevin Hainline/JADES

Prior to JADES, astronomers had identified only a few dozen galaxies from this period, but JWST has now found nearly a thousand. This came as a surprise to astronomers because they had no idea there were so many early galaxies. In fact, JADES has found 717 galaxies since the universe was between 370 million and 650 years old, though many of them need further confirmation. He also found the most distant galaxy seen by humans to date, JADES-GS-z13-0, which has a redshift of 13.2 and a light travel time of 13.395 billion years. Not only did he find them, but JWST’s take on them is far more detailed than any previous observations.

“Over 93% of the sources in this study have never been seen before.”

Kevin Hainline, JADES, University of Arizona at Tucson

“Previously, the first galaxies we could see just looked like small specks. Yet those spots represent millions or even billions of stars at the beginning of the universe,” said Kevin Hainline, part of the team that used JWST’s NIRCam to measure redshifts of galaxies. “Now we can see that some of they are actually extended objects with visible structure. We can see clusters of stars being born only a few hundred million years after the beginning of time.”

Kevin Hainline presented some of JADES’ findings at this week’s AAS 242 meeting. His presentation starts at 17:00. He talks about the first 600 million years after the Big Bang. “It’s an amazing thing that we can even talk about it, thanks to the JWST,” Hainline said. “Over 93% of the sources in this study have never been seen before.”

What is the JWST’s view on these early stars telling astronomers? “We’re finding that star formation in the early universe is much more complicated than we thought,” added Rieke.

One of JADES’ surprising results is a quiescent galaxy just 730 million years after the Big Bang. Quiescent galaxies no longer form stars after they run out of gas. How could this happen so soon?

What about black holes? What effect did they have on the first galaxies? JADES will help find active galactic nuclei (AGN) that are highly luminous when accreting material from a galaxy’s black hole. What role did black hole feedback play in the early Universe? “Finding the connection between galaxy growth and black hole growth is a key factor, which we hope to clarify when our samples are more complete,” writes the JADES team.

The first stars and galaxies in the Universe shaped the Universe into what it is now. By reionizing hydrogen, the first stars triggered the transition from opaque to transparent during the Epoch of Reionization, ending the Dark Ages of the Universe. But there are things we don’t know.

When exactly did the first stars form? Why were there so many massive and hot stars compared to now? Early galaxies may have consisted mostly of dark matter, but not in halos around modern galaxies. Instead, it was mixed with normal matter. What role did it play?

The early Universe consisted of hydrogen, helium and light. Somehow, these three things have combined to create the complexity we see all around us today. We have a long list of questions about what happened and how things became what they are today.

Astronomers don’t have answers to all these questions and for a long time the observational evidence was scarce and it was left mostly to theory to figure it all out. The venerable Hubble Space Telescope helped, but now we have the JWST, our most powerful tool for studying the early Universe. It is not yet certain whether JADES can generate answers to these questions. But don’t bet against it.

The JADES team is publishing 14 new papers and these papers are helping astronomers find answers.

Moreover:

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