Webb Observations Indicate Early Galaxies Had Extended and Elongated Shapes, Challenging Disk and Spherical Models

January 17, 2024

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Conducted by researches from Columbia University

A recent study by Columbia University researchers that has analyzed images from NASA's James Webb Space Telescope revealed that galaxies in the early universe are predominantly flat and elongated, as opposed to round.

'Between 50 to 80% of the galaxies we researched appear to be two-dimensionally flattened,' said Viraj Pandya, a NASA Hubble Fellow at Columbia University, and the lead researcher of a new paper showcasing these findings, which will be published in The Astrophysical Journal.

'Extended, slender galaxies, much like a breadstick, were prevalent in the early universe, unforeseen considering their scarcity among the galaxies in the contemporary universe.'

The research group harvested galaxies from the vast near-infrared image repository provided by Webb's Cosmic Evolution Early Release Science (CEERS) Survey, from a period when the universe was between 600 million and 6 billion years old.

Studied galaxies revealed shapes ranging from breadstick-like to that of pizza pies and spheres. The least frequently identified were spherical galaxies, similar in size to a ball of pizza dough. These were found to be the smallest types of galaxies. The long axis of pizza pie-shaped galaxies was measured to be similar in length to the breadstick-shaped galaxies. 'They are more noticeable in the closer universe, which contains older and more developed galaxies due to the universe's continued expansion.'

What form would our Milky Way galaxy have assumed if we could travel billions of years back in time? 'Our best guess is that it would have resembled a breadstick,' suggested co-researcher Haowen Zhang, a Ph.D. candidate at the University of Arizona in Tucson. This theory is based partly on new data from the Webb telescope, which was used to estimate the mass of the Milky Way billions of years ago, hinting at a possible elongated appearance in ancient times.

These distant galaxies are significantly less substantial than neighboring spirals and ellipticals—they serve as precursors to more massive galaxies like ours. 'In the early universe, galaxies had less time to grow,' noted Kartheik Iyer, another NASA Hubble Fellow from Columbia University.

'The identification of additional early galaxy shapes is fascinating, providing us with more data to evaluate. We are now in a position to understand how galaxies' shapes relate to their appearance and can predict how they originated in greater detail.'

Marc Huertas-Company, a faculty research scientist from the Institute of Astrophysics on the Canary Islands and another collaborator on the study pointed out that the Hubble Space Telescope, which was launched in 1990 and continues to collect data, has long revealed an overrepresentation of elongated galaxies. The team wondered if using the Webb telescope, launched in 2021, would provide additional details due to its sensitivity to infrared light.

'The Webb telescope confirmed that Hubble didn't miss any additional features in the galaxies they both observed. Moreover, Webb displayed many more similar-shaped distant galaxies in high detail,' Huertas-Company stated.

One theory, according to Pandya, is that elongation and flatness of early galaxies could be attributed to skeletal networks of dark matter in the early universe that formed 'cosmic highways,' guiding the formation of gas and stars. These filaments remain, although they have become sparser due to the universe's expansion, making the formation of breadstick-shaped galaxies less likely.

The researchers humorously titled the paper 'Galaxies Going Bananas.' When they graphed galaxies' aspect ratios against their longest axis length, they discovered that the resulting diagrams resembled bananas, a shape that mirrors their elongated, breadstick-like form.

'To use the banana analogy, these intrinsically elongated galaxies seem to have been the prevalent type in the first 4 billion years of the universe,' added Pandya.

Despite these findings, some uncertainties remain. To further demystify the properties and exact locations of these distant galaxies, researchers need a larger sample size from the Webb telescope and must devote considerable time to refine their models to reflect the precise geometries of these distant galaxies more accurately.

'These are early results,' said co-author Elizabeth McGrath, an associate professor at Colby College in Waterville, Maine. 'We need to delve more deeply into the data to figure out what's going on, but we're very excited about these early trends.'

Provided by Columbia University