JWST exhibits how the early universe frantically shaped stars

We can peer into regions in our vicinity to the Milky Way and witness orgies of star formation. The closest region is in the Orion Nebula, where astronomers have identified more than 700 young stars. They range from just 100,000 years – still in its infancy for a star – to over a million years.

But we are now more than 13 billion years after the Big Bang. What did star formation look like back when the conditions in the universe were still 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 imaging and spectroscopic survey of galaxies from about z~12 to z~2, about 370 million to 3.3 billion years after the Big Bang. His goal is to understand the formation and evolution of these galaxies and their stars in the early days of the universe, one of the great questions in astronomy.

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“In the past, the earliest galaxies we could see just looked like little blobs. And yet these spots represent millions or even billions of stars at the beginning of the universe.”

Kevin Hainline, University of Arizona at Tucson

JADES revisits a region of the sky familiar to astronomy fans: the Hubble Ultra Deep Field (HUDF). The HUDF is a low-field image of a small region of sky taken over 11 observing days over months by the Hubble Space Telescope capture. It contains about 10,000 galaxies, and the smallest and reddest are from when the Universe was only about 800 million years old.

The JADES program uses two of the JWST’s instruments together – NIRSpec (Near-Infrared Spectrograph) and NIRCam (Near-Infrared Camera) – to study the region in and around the HUDF in more detail and detail. The experiment required 770 hours of observation time. The JADES team has already identified hundreds of galaxies from when the Universe was less than 600 million years old. Some of them are full of hot young stars.

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

The background to these questions concerns the epoch of reionization (EOR) of the universe.

The EOR occurred within a billion years of the Big Bang. Previously, 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 the hydrogen reionized 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. Image credits: 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 the EOR. Ryan Endsley of the University of Texas at Austin led this research. Endsley and his colleagues used JWST’s NIRSpec instrument to look for signs of star formation in these galaxies. They found it in abundance.

“Almost every single galaxy we find has these unusually strong emission line signatures, which indicate intense recent star formation. “These early galaxies were very good at making hot, massive stars,” Endsley said.

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

The JADES team created an interactive tool to explore the imagery of the JWST. Lose yourself in it and marvel at some of the first galaxies ever to form in the universe. Photo credit: JADES

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

To understand the early Universe, astronomers must observe it. This is the strength of the JWST. Part of JADES focuses on galaxies that existed when the Universe was less than 400 million years old. These galaxies can help answer the question of how different star formation was then compared to now. The light from these galaxies is redshifted due to the expansion of the universe, and astronomers measure redshift to determine 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 few hundred million years after the first stars and galaxies formed.

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

Before JADES, astronomers had only identified a few dozen galaxies from this period, but the JWST has now found almost a thousand of them. This came as a surprise to astronomers who had no idea there were so many early galaxies. In fact, JADES has found 717 galaxies from when the Universe was between 370 million and 650 years old, although many of them require further confirmation. Also found was the furthest human-observed galaxy 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 it find them, but JWST’s view of 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

“In the past, the earliest galaxies we could see just looked like little splotches. And yet these 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 the redshifts of galaxies. “Now we can see that some of them are actually extended objects with visible structure. We can see clusters of stars forming just a few hundred million years after time began.”

Kevin Hainline presented some of the findings from JADES at this week’s AAS 242 meeting. His lecture begins at 5:00 p.m. He talks about the first 600 million years after the Big Bang. “It’s amazing that we can even talk about this thanks to JWST,” Hainline said. “Over 93% of the sources in this study have never been seen before.”

What view does the JWST share with astronomers about these early stars? “We find that star formation in the early universe is much more complicated than we thought,” added Rieke.

One of the surprising results from JADES is a galaxy at rest just 730 million years after the Big Bang. Dormant galaxies stop forming stars when they run out of gas. How could that happen so quickly?

What about black holes? What effect did they have on early galaxies? JADES will help find active galactic nuclei (AGN) that glow brightly as a galaxy’s black hole accumulates material. What role did black hole feedback play in the early universe? “Finding the link between galaxy growth and black hole growth is an important factor that we hope to elucidate as our samples become more complete,” the JADES team writes.

The universe’s first stars and galaxies made it what it is today. 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, hot stars compared to today? The first galaxies may have consisted mostly of dark matter, but not 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 combined created the complexity we see around us today. We have a long list of questions about what happened and how things got where they are today.

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

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


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