The earliest galaxies in the universe are thought to have formed around 400 million years after the Big Bang, during a period known as “cosmic dawn.” These early galaxies were small and faint, and they were primarily composed of hydrogen and helium. They likely formed through the collapse of small density fluctuations in the early universe, which led to the formation of the first stars and galaxies. The study of these early galaxies can help us understand the processes that led to the formation and evolution of the universe as we know it today. The James Webb Space Telescope, set to launch in 2021, will be able to study these early galaxies in more detail.
Astronomers used data from NASA’s James Webb Space Telescope (JWST) Early Release Observations to discover 87 galaxies that may be the universe’s earliest known galaxies. The discovery brings astronomers one step closer to determining when galaxies first appeared in the universe, which is estimated to be 200-400 million years after the Big Bang.
A team of astronomers led by Haojing Yan at the University of Missouri discovered 87 galaxies that could be the universe’s earliest known galaxies using data from NASA’s James Webb Space Telescope (JWST) Early Release Observations in a new study.
The finding moves astronomers one step closer to finding out when galaxies first appeared in the universe – about 200-400 million years after the Big Bang, said Yan, associate professor of physics and astronomy at MU and lead author on the 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. Our finding gives us the first indication that a lot of galaxies could have been formed in the universe much earlier than previously thought.Haojing Yan
“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 a lot of galaxies could have been formed in the universe much earlier than previously thought.”
The astronomers looked for potential galaxies at “very high redshifts” in the study. According to Yan, the concept of redshifts in astronomy allows astronomers to measure how far away distant objects in the universe, such as galaxies, are by looking at how the colors change in the waves of light that they emit.
“When a light-emitting source moves toward us, the light is ‘squeezed,’ and the shorter wavelength is represented by blue light, or blueshift,” Yan explained. “However, if that source [of light] moves away from us, the light it produces is ‘stretched,’ changing to a longer wavelength represented by red light, or redshift.”
Yan said Edwin Hubble’s discovery in the late 1920s that our universe is ever-expanding is key to understanding how redshifts are used in astronomy.
“Hubble confirmed that galaxies external to our Milky Way galaxy are moving away from us, and the more distant they are, the faster they are moving away,” Yan said. “This relates to redshifts through the notion of distances — the higher the redshift an object is at, such as a galaxy, the further away it is from us.”
Therefore, Yan said the search for galaxies at 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 over a distance to reach us,” Yan said. “For example, when we look at the sun, we aren’t looking at it as what it looks like in the present, but rather what it looked like some eight minutes ago. That’s because that’s how long it takes for the sun’s radiation to reach us. So, when we are looking at galaxies which are very far away, we are looking at their images from a long time ago.”
Yan’s team used this concept to identify the galaxies by analyzing infrared light captured by the JWST. “The higher a galaxy’s redshift, the longer it takes for light to reach us, so a higher redshift corresponds to an earlier view of the universe,” Yan explained. “As a result, we are getting earlier snapshots of what the universe looked like a long time ago by looking at galaxies at higher redshifts.”
According to Yan, the JWST was critical to this discovery because objects in space, such as galaxies at high redshifts (11 and above), can only be detected by infrared light. This is beyond the capabilities of NASA’s Hubble Space Telescope, which only sees light in the ultraviolet to near-infrared range.
“The most powerful infrared telescope, JWST, has the sensitivity and resolution for the job,” Yan explained. “Most astronomers believed that the universe should have very few galaxies beyond redshift 11 until the first JWST data sets were released [in mid-July 2022]. At the very least, our findings call this viewpoint into question. I believe this is just the tip of the iceberg because the data we used was limited to a very small portion of the universe. Following this, I expect other teams of astronomers to find similar results elsewhere in the vast reaches of space as JWST continues to provide us with a new perspective on the deepest parts of our universe.”