A projected image of the galaxy JD1 (inset), which is located behind the galaxy cluster Abell 2744. Image credit: Guido Roberts-Borsani, UCLA / NASA / ESA / CSA / Swinburne University of Technology / University of Pittsburgh / STScI.
The first billion years of the Universe’s life were a crucial period in its evolution.
After the Big Bang, approximately 13.8 billion years ago, the early Universe expanded and cooled sufficiently for hydrogen atoms to form.
Hydrogen atoms absorb ultraviolet photons from young stars; however, until the birth of the first stars and galaxies, the Universe became dark and entered a period known as the cosmic dark ages.
The appearance of the first stars and galaxies a few hundred million years later bathed the Universe in energetic ultraviolet light which began burning, or ionizing, the hydrogen fog. That, in turn, enabled photons to travel through space, rendering the Universe transparent.
Determining the types of galaxies that dominated that era — dubbed the epoch of reionization — is a major goal in astronomy today, but until the development of the NASA/ESA/CSA James Webb Space Telescope, astronomers lacked the sensitive infrared instruments required to study the first generation of galaxies.
“Most of the galaxies found with Webb so far are bright galaxies that are rare and not thought to be particularly representative of the young galaxies that populated the early Universe,” said Dr. Guido Roberts-Borsani, a postdoctoral researcher at the University of California, Los Angeles.
“As such, while important, they are not thought to be the main agents that burned through all of that hydrogen fog.”
“Ultra-faint galaxies such as JD1, on the other hand, are far more numerous, which is why we believe they are more representative of the galaxies that conducted the reionization process, allowing ultraviolet light to travel unimpeded through space and time.”
Abell 2744 is about 4 billion light-years away, some 350 million light-years across, and has a mass equivalent to more than 4 trillion solar masses.
The cluster combined gravitational strength bends and amplifies the light from JD1, making the faint galaxy appear larger and 13 times brighter than it otherwise would.
“Because light takes time to travel to Earth, JD1 is seen as it was approximately 13.3 billion years ago, when the Universe was only about 4% of its present age,” they explained.
The authors used the new data to trace JD1’s light back to its original source and shape, revealing a compact galaxy just a fraction of the size of older galaxies like the Milky Way.
“Before Webb switched on, just a year ago, we could not even dream of confirming such a faint galaxy,” said Professor Tommaso Treu, an astronomer at the University of California, Los Angeles.
“The combination of Webb and the magnifying power of gravitational lensing is a revolution.”
“We are rewriting the book on how galaxies formed and evolved in the immediate aftermath of the Big Bang.”
Source: Sci News