Researchers at Columbia University analyzed images taken by NASA's James Webb Space Telescope and found that galaxies in the early universe were often flat and elongated, like baguettes, and rarely round, like pizza dough.
The shape of a sample of distant galaxies as determined by the James Webb Space Telescope's Cosmic Evolution Early Release Science (CEERS) survey. Source: NASA, ESA, CSA, STScI, Steve Finkelstein (UTAustin), Micaela Bagley (UTAustin), Rebecca Larson (UTAustin)
"About 50 to 80 percent of the galaxies we studied appear to be flat in two dimensions," explained Viraj Pandya, a NASA Hubble researcher at Columbia University. "Galaxies that look like elongated breadsticks appear to have grown in size early on." "They are very common in the early universe, which is surprising because they are not common in galaxies in the present-day universe," he is the lead author of a new paper to be published in The Astrophysical Journal outlining the discovery.
The team focused on a large collection of near-infrared images provided by the Webb telescope, known as the Cosmic Evolution Early Release Science (CEERS) survey, to single out galaxies estimated to have existed when the universe was 600 million to 6 billion years old.
Most distant galaxies look like baguettes, while others are shaped like pizza slices and pizza dough balls. This group of galaxies appears to be the smallest type of galaxy and the least common. Pizza-shaped galaxies are as large as baguette-shaped galaxies on their longest axis. They are more common in the nearby universe, which is made up of older, more mature galaxies due to the expansion of the universe.
The past shape of the Milky Way and the evolution of galaxies
If we could turn back the clock billions of years ago, which category would the Milky Way belong to? "Our best guess is that it might have looked more like a breadstick," said co-author Haowen Zhang, a doctoral student at the University of Arizona in Tucson. "This hypothesis is based in part on new evidence from the Webb Telescope, which theorists have used to estimate the mass of the Milky Way billions of years ago, suggesting that it was likely to have been shaped like a breadstick in the distant past."
These distant galaxies are also much less massive than nearby spiral and elliptical galaxies - they are the precursors to more massive galaxies like ours. "In the early universe, galaxies had a much shorter time to grow," said co-author Kartheik Iyer of Columbia University and NASA Hubble Fellow. "Identifying other classes of early galaxies is exciting - there is now much more to analyse. We can now study the relationship between the shape of galaxies and their appearance, and better predict how they formed in greater detail."
The Hubble Space Telescope was launched in 1990 and is still collecting data today. "Hubble has long shown many elongated galaxies," explained Hubble co-author Marc Huertas-Company, a research scientist at the Institute of Astrophysics Canary Islands. But researchers still want to know: Will the Webb telescope, due to be launched in 2021, be better at showing more detail because it is more sensitive to infrared light? "Webb confirmed that Hubble did not miss any additional features in the galaxies they observed at the same time. In addition, Webb showed us many more distant galaxies with similar shapes, and all in great detail," said Huertas-Company.
Understanding the shapes of early galaxies
One question, of course, is why early galaxies tend to be so flat and elongated. One hypothesis, Pandya explained, is that the early universe may have been filled with dark matter filaments that formed a "skeletal background" or "cosmic highway" that directed gas and stars into it. These filaments are still present, but as the universe expanded, they became more dispersed, so they may be less likely to contribute to the formation of bread-shaped galaxies.
"Galaxies gone mad" and future research
The paper is called "Galaxies Going Bananas," another food analogy that came to the authors while studying the data. When the authors compared the aspect ratios of galaxies to the length of their longest axis, they found that the resulting graph looked a lot like bananas, a shape that mirrored their elongated ellipsoidal (i.e. breadstick) shape. "Banana is another way of saying that these essentially elongated galaxies appear to have been the dominant galaxies in the first 4 billion years of the universe," Pandya said.
Not only do researchers need a larger Webb sample size to further refine the properties and precise locations of distant galaxies, they also need to spend considerable time adjusting and updating their models to better reflect the precise geometries of distant galaxies. "These are just early results," said co-author Elizabeth McGrath, an associate professor at Colby College in Waterville, Maine. "We'll need to dig deeper into the data to figure out exactly what's going on, but we're very excited about these early trends."
Compiled source: ScitechDaily