Growth of “inside-out” galaxies observed in the early universe

Astronomers used the NASA/ESA James Webb Space Telescope (JWST) to observe the “inside-out” growth of galaxies in the early Universe, just 700 million years after the Big Bang.

This galaxy is 100 times smaller than the Milky Way, but it is surprisingly mature for such an early universe. Similar to large cities, the center of this galaxy has a high density of stars, but the “outskirts” of the galaxy have a lower density of stars. And just like any big city, this galaxy is starting to expand, with star formation accelerating in its suburbs.

This is the earliest detection in history of the inside-out growth of a galaxy. Until Webb, it had been impossible to study the growth of galaxies this early in the universe’s history.

Although the images obtained with the Webb represent a snapshot in time, by studying similar galaxies, researchers led by the University of Cambridge have determined how galaxies evolved from gas clouds to the complex structures observed today. He says that this could be useful in understanding how things change. Results will be reported in a journal natural astronomy.

“The question of how galaxies evolve over cosmic time is an important question in astrophysics,” said co-lead author Dr. Sandro Tacella of the Cavendish Laboratory at the University of Cambridge.

“We’ve had a lot of great data about galaxies over the past 10 million years and in our remote corners of the universe, and now we can use the Web to take observations from billions of years ago and explore the first billion years of the universe. History brings up all sorts of new questions.”

The galaxies we observe today grow by two main mechanisms. It either draws in or accretes gas to form new stars, or it grows by merging with smaller galaxies. Whether different mechanisms were at work in the early universe is an open question that astronomers hope to address with Webb.

“We expect galaxies to start small as gas clouds collapse under their own gravity, forming very dense stellar nuclei and possibly black holes,” Tacchera said.

“As galaxies grow and star formation increases, it’s like a spinning figure skater. When the skater pulls back on his arm, he gains momentum and spins faster and faster. The longer distances cause the galaxies to rotate, which is why they often form spirals or disk shapes.

This galaxy was observed as part of the JADES (JWST Advanced Extragalactic Exploration) joint research, and is actively forming stars in the early Universe. This galaxy has a very dense core, similar in density to modern giant elliptical galaxies with 1,000 times as many stars, despite its relatively young age. Most star formation occurs further away from the center, with star-forming “clumps” further out.

Star formation activity is strongly increasing toward the periphery, and star formation is spreading and the galaxy is growing larger. This kind of growth was predicted by theoretical models, but using Webb it is now possible to observe it.

“One of the many reasons why Webb was such a game changer for us astronomers is that it allowed us to observe things that were previously predicted through modeling,” said co-author Dr. William Baker. states. Cavendish student. “It’s like being able to check your homework.”

Researchers used the Webb to extract information from the light emitted by galaxies at different wavelengths and used it to estimate the number of young and old stars, determine stellar mass and star formation. I converted it into a speed estimate.

Because galaxies are so compact, individual images of galaxies were “forward modeled” to account for instrumental effects. Using stellar population modeling, including prescriptions for gas outflow and dust uptake, the researchers found that while there are old stars in the core, very active star formation is occurring in the surrounding disk. I discovered that there is.

The galaxy doubles the mass of its outlying stars approximately every 10 million years, which is extremely rapid. The Milky Way’s mass doubles every 10 billion years.

The density of the galactic nucleus and high star formation rate suggest that this young galaxy is rich in the gas needed to form new stars, which may reflect different conditions in the early Universe. There is a gender.

“Of course, this is just one galaxy, so we need to know what other galaxies were doing at the time,” Tatchera says.

“Are all galaxies like this? We are currently analyzing similar data from other galaxies. By observing different galaxies across cosmic time, we can reconstruct the growth cycle.” “We may be able to demonstrate how galaxies grow to their final size today.”