The James Webb Space Telescope witnesses the dawn of starlight

Leading notes by James Webb Space Telescope Results of early galaxy mergers indicate stars formed faster and more efficiently than previously known, revealing complex star clusters and challenging current cosmological theories.

• Galaxies and stars evolved faster yet the great explosion Than expected.
• Detailed images of one of the first galaxies show that growth was much faster than we thought.

An international research team has made unprecedented detailed observations of the first galaxy merger ever. They suggest that stars evolved faster and more efficiently than we thought.

They used the James Webb Space Telescope (JWST) to observe the massive object as it existed 510 million years after the Big Bang – about 13 billion years ago.

“When we made these observations, this galaxy was 10 times larger than any other galaxy discovered in the early universe,” says Dr Kit Boyett, ASTRO 3D Research Fellow in Early Galaxies, from the University of Melbourne. He is the lead author of a paper recently published in Nature astronomy. The paper includes 27 authors from 19 institutions in Australia, Thailand, Italy, USA, Japan, Denmark and China.

The James Webb Space Telescope, launched in 2021, allows astronomers to view the early universe in ways that were previously impossible. Objects that appeared as single points of light through previous telescopes e.g Hubble Space Telescopereveals its complexity.

The James Webb Space Telescope shows details of a massive galaxy merger 13 billion years ago. Credit: Astro 3D

“It is amazing to see the power of the James Webb Space Telescope to provide a detailed view of galaxies at the edge of the observable universe, thus going back in time,” says Professor Michel Trinity, ASTRO 3D First Galaxies subject leader and contract leader at the University of Melbourne. Professor Trinity adds: “This space observatory changes our understanding of early galaxy formation.”

The observations in the current paper show a galaxy consisting of several clusters with two components in the main cluster and a long tail, indicating an ongoing merger of two galaxies into a larger galaxy.

“The merger is not over yet. We can tell that by the fact that we can still see two objects. The long tail is likely the result of some material being thrown aside during the merging process. When two objects fuse, they get rid of some matter,” says Dr. Boyett. “This tells us that there is a merger and this is the farthest merger ever.”

These and other observations using the James Webb Space Telescope are prompting astrophysicists to revise their models of the universe's early years.

“With James Webb, we see more objects in the early universe than we expect to see, and these objects are more massive than we thought, too,” says Dr. Boyett. “Our cosmology is not necessarily wrong, but our understanding of how quickly galaxies form may be, because they are larger in size than we thought possible.”

Other ancient galaxies. Credit: Astro 3D

The findings by Dr. Boyett's team show that these galaxies were able to accumulate mass very quickly by merging.

But it's not just the size of the galaxies and the speed at which they grow that surprised Dr. Boyett. His paper describes for the first time the number of stars that make up the merging galaxies, another detail made possible by the James Webb Space Telescope.

“When we compared our spectroscopic analysis with our imaging, we found two things that were different. The image told us that the number of stars was small, but the spectroscopy spoke of very old stars. But it turns out that both are true,” Boyett says. Because we have not one group of stars, but two.”

“The old residents have been there for a long time and what we think is happening is that the merging of galaxies is producing new stars and that's what we see in the imaging – new stars on top of the old residents.”

Most studies of these distant objects show very young stars, but this is because younger stars are brighter and so their light dominates the imaging data. However, the James Webb Space Telescope allows for such detailed observations that the two groups can be distinguished.

“The fact is that spectroscopy is so detailed that we can see the subtle features of ancient stars that actually tell us that there is more out there than we think,” says Dr. Boyett.

“This is not entirely surprising, as we know that throughout the history of the universe there are peaks of new star formation for various reasons, and this leads to multiple populations.

“But this is the first time we've really seen them at this distance.”

The paper has major implications for current modeling.

“Our simulations could produce an object similar to the one we observed, roughly the same age as the universe, and with roughly the same mass. However, it is extremely rare. Very rare, there is only one of them in the entire model. The chance of observing “Our observations suggest we're either very lucky or our simulations are wrong, and this kind of thing is more common than we think.”

“The thing we think we're missing is that stars were forming more efficiently, and that might be what we need to change in our models.”

Reference: “A massive interacting galaxy 510 million years after the Big Bang” by Kristan Boyett, Michele Trinti, Nisha Lithokawalit, Antonello Calabro, Benjamin Metha, Guido Roberts Borsani, Niccolò Dalmaso, Lilan Yang, Paola Santini, Tommaso Trio, Tucker Jones. Alaina Henry, Charlotte A. Mason, Takahiro Morishita, Themia Nanayakkara, Namrata Roy, Chen Wang, Adriano Fontana, Emiliano Merlin, Marco Castellano, Diego Paris, Marusha Bradac, Matt Malkan, Danilo Marchesini, Sara Mascia, Karl Glezbrook, Laura Pinterici. , Eros Vanzella and Benedetta Vulcani, March 7, 2024, Nature astronomy.
doi: 10.1038/s41550-024-02218-7