Looking for the first galaxies in the universe // Show me Mizzou // University of Missouri
January 11, 2023
Contact: Eric Stann, 573-882-3346, StannE@missouri.edu
In a new study, a team of astronomers led by Haojing Yan at the University of Missouri used data from NASA’s James Webb Space Telescope (JWST) Early Release Observations and discovered 87 galaxies that could be the first known galaxies in the universe.
The finding brings astronomers one step closer to finding out when galaxies first appeared in the universe, some 200-400 million years after the Big Bang, said Yan, associate professor of physics and astronomy at MU and lead author of the paper. study.
“Finding such a large number of galaxies in the early parts of the universe suggests that we might need to revise our previous understanding of galaxy formation,” Yan said. “Our finding gives us the first indication that many galaxies could have formed in the universe much earlier than previously thought.”
In the study, the astronomers searched for potential galaxies at “very high redshifts.” Yan said the concept of redshift in astronomy allows astronomers to measure how far away distant objects are in the universe, such as galaxies, by looking at how colors change in the light waves they emit.
“If a light-emitting source is moving towards us, the light is being ‘squeezed’ and that shorter wavelength is represented as blue light or blueshift,” Yan said. But if that source [of light] is moving away from us, the light it produces is ‘stretched’ and changes to a longer wavelength that is represented by red light or redshift”.
Yan said Edwin Hubble’s discovery in the late 1920s that our universe is constantly expanding is key to understanding how redshifts are used in astronomy.
“Hubble confirmed that galaxies outside our Milky Way are receding from us, and the more distant they are, the faster they are receding,” Yan said. “This relates to redshifts through the notion of distances: the higher the redshift an object, such as a galaxy, is at, the further away it is from us.”
Therefore, Yan said that the search for galaxies with very high redshifts gives astronomers a way to construct the early history of the universe.
“The speed of light is finite, so it takes time for light to travel a distance to reach us,” Yan said. “For example, when we look at the sun, we don’t see it as it looks today, but as it looked about eight minutes ago. That’s because that’s how long it takes radiation from the sun to reach us. So when we’re looking at galaxies that are very far away, we’re looking at their images from a long time ago.”
Using this concept, Yan’s team analyzed the infrared light captured by the JWST to identify the galaxies.
“The greater the redshift of a galaxy, the longer it takes for light to reach us, so a greater redshift corresponds to an earlier view of the universe,” Yan said. “Thus, by looking at galaxies with higher redshifts, we get earlier snapshots of what the universe looked like a long time ago.”
The JWST was critical to this discovery because objects in space such as galaxies that are at high redshifts (11 and above) can only be detected using infrared light, according to Yan. This is beyond what NASA’s Hubble Space Telescope can detect because the Hubble telescope only sees from ultraviolet to near-infrared light.
“JWST, the most powerful infrared telescope, has the sensitivity and resolution for the job,” Yan said. “Until these first JWST data sets were published [in mid-July 2022], most astronomers believed that the universe should have very few galaxies beyond redshift 11. At the very least, our results challenge this view. I think this discovery is just the tip of the iceberg because the data we used was only focused on a very small area of the universe. Following this, I anticipate that other teams of astronomers will find similar results elsewhere in the vast reaches of space as JWST continues to give us new insights into the deepest parts of our universe.”
“First batch of z ≈ 11–20 candidate objects revealed by James Webb Space Telescope early launch observations in SMACS 0723-73”, was published in The letters of the astrophysical journal. Co-authors are Chenxiaoji Ling at MU; Zhiyuan Ma at the University of Massachusetts-Amherst; and Cheng Cheng and Jia-Sheng Huang at the Astronomy Center of the Chinese Academy of Sciences of South America and the National Astronomical Observatories of China.