Pune: Researchers at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, have found that some of the earliest known galaxies were already surprisingly well organised less than a billion years after the Big Bang.
Event Context
Using deep images captured by the National Aeronautics and Space Administration’s (NASA) James Webb Space Telescope (JWST), the team discovered that these ancient galaxies obey a fundamental rule of galaxy structure known as the Kormendy relation—a scaling law that links the size of a spheroidal (rounded) galaxy to its surface brightness.
The study was published on July 2 this year in the IOP Science journal.
The finding pushes one of the cornerstones of galaxy evolution much further back in cosmic history than previously known, suggesting that the physical processes shaping galaxies were already at work during the Universe’s earliest stages.
Player Focus
The discovery suggests that the first spheroidal galaxies reached a surprising level of structural maturity much earlier than many theoretical models had predicted.
It also implies that the mechanisms responsible for organising galaxies into the familiar elliptical structures seen today emerged soon after the first generations of galaxies formed.
The findings provide a new benchmark for galaxy formation theories. Future computer simulations will now have to explain not only how the earliest massive galaxies formed so quickly, but also why they already followed the same structural laws that govern galaxies nearly 13 billion years later.
In other words, the study suggests the Universe learned the rules of galaxy building much earlier than astronomers had previously imagined.
Team Analysis
Astronomers have long believed that galaxies in the young Universe were clumpy, chaotic and rapidly evolving systems that had not yet settled into stable structures. To test this, the IUCAA team analysed publicly available JWST observations of hundreds of distant galaxies that existed when the Universe was just 400 million to 900 million years old (at redshifts greater than six).
By measuring how light is distributed across these galaxies, the researchers examined whether these “baby galaxies” followed the same structural relation observed in nearby spheroidal galaxies.
The Kormendy relation states that galaxies with brighter central surface brightness tend to be more compact. Astronomers have used this scaling relation for decades as a benchmark for understanding the structure and evolution of spheroidal galaxies.
Anshuman Borgohain, the study’s lead author and a post-doctoral fellow at IUCAA, said, “The unprecedented capabilities of JWST continue to reveal exciting findings about the earliest galaxies, challenging our current understanding of how they grew and evolved in the infant Universe. Our findings will help establish a new benchmark for understanding early galaxy assembly.”
Prof Kanak Saha, who supervised the project, said scaling relations such as the Kormendy relation serve as “fossil records” of galaxy evolution because they preserve the cumulative effects of gravity, star formation, mergers and gas dynamics over cosmic time.
Match Outlook
“Until the launch of JWST, astronomers could measure these relations only for relatively nearby galaxies or systems observed several billion years after the Big Bang. The first billion years remained largely inaccessible because earlier telescopes lacked the sensitivity and resolution to study such distant objects. JWST has now opened that frontier,” Saha said.
