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For more than a century, astronomers have categorized galaxies near and far, both by comparing their shapes by eye and precisely measuring their properties with data known as spectra. For example, Edwin Hubble created the Hubble Tuning Fork in 1926 to begin to sort the shapes and sizes of nearby galaxies, showing that many are spirals and ellipticals.
As telescopes’ instruments have become increasingly more sensitive, it is easier to more accurately classify their shapes. New data from the James Webb Space Telescope have added nuances to astronomers’ classifications. Since Webb observes in infrared light, many more extremely distant galaxies appear in its images. Plus, the images are finely detailed, allowing researchers to identify if there are additional areas of star formation – or confirm they aren’t present.
A team led by Viraj Pandya, a NASA Hubble Fellow at Columbia University in New York, recently analyzed hundreds of distant galaxies in Webb’s Cosmic Evolution Early Release Science (CEERS) Survey. CEERS intentionally covers much of the same area as the Hubble Space Telescope’s Extended Groth Strip, which was one of the five fields used to create the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This allowed them to double-check Webb’s results where the telescopes’ observations overlap.
“Our analysis of Webb’s galaxies was very consistent with galaxies in the Hubble Space Telescope catalog,” Pandya confirmed. “Two sets of data allowed us to fully vet our models as we ran our analysis, and better understand and categorize galaxies that only Webb detected.” The team began their analysis by sorting the galaxies into broad classes based on similar characteristics. (They did not classify each galaxy’s individual appearance since that would require detailed information from data known as spectra.)
They found an array of odd shapes when the universe was 600 million to 6 billion years old. The galaxy shapes that dominate look flat and elongated, like pool noodles or surfboards. These two galaxy types make up approximately 50 to 80% of all the distant galaxies they studied – a surprise, since these shapes are rare closer to home.
Other galaxies Webb detected appear round but also flattened, like frisbees. The least populated category is made up of galaxies that are shaped like spheres or volleyballs.
Webb’s data also resolved a riddle that was introduced by the Hubble Space Telescope’s observations decades ago. Why do so many distant galaxies appear like long lines? Was there more to the galaxies that didn’t appear in its images? Webb answered this in short order: Hubble hasn’t missed anything.
“Webb confirmed what Hubble has long shown us, but in greater detail in infrared light,” Pandya said. “Their combined observations show that in the early universe, many more galaxies appear flat and elongated. This has profound implications, since we usually assume that galaxies like our own Milky Way started out as disks, but that may not be the case.”
Why do galaxies have such different shapes early in the history of the universe? This question remains unanswered for now, but research is underway to better understand how galaxies evolved over all of cosmic time.
