The universe, an expanse of unimaginable scale, has always captivated human curiosity. A fundamental question is what is the farthest thing we can possibly see? This inquiry propels astronomers to push observational boundaries, continuously redefining what is considered “farthest.” New discoveries offer insights into the universe’s earliest moments and its ongoing evolution.
Discovering the Farthest Galaxies
The quest for the farthest individual object leads astronomers to distant galaxies and quasars. The current record holder is galaxy JADES-GS-z14-0, observed as it existed approximately 290 million years after the Big Bang. Discovered in May 2024 by the James Webb Space Telescope (JWST), its light traveled about 13.5 billion years to reach us.
Before JADES-GS-z14-0, JADES-GS-z13-0 held the record, confirmed in 2022 with a light-travel distance of 13.4 billion years, appearing 325 million years after the Big Bang. Another past candidate, HD1, identified in 2022, was initially estimated to be 13.5 billion light-years away, existing 330 million years after the Big Bang. Its distance, however, required further spectroscopic confirmation.
Previously, GN-z11, discovered in 2016 by the Hubble Space Telescope, was considered the most distant, seen 400 million years after the Big Bang. These faint objects represent the first generations of galaxies, forming stars and potentially hosting early supermassive black holes. Observing them provides a window into the “Cosmic Dawn,” when the universe’s first luminous structures emerged.
How Distances are Measured
Determining distances to remote cosmic objects relies on a phenomenon called redshift. As light travels through the expanding universe, its wavelengths stretch, shifting towards the red end of the electromagnetic spectrum. The greater an object’s redshift, the faster it moves away, and the farther away it is.
Hubble’s Law describes the relationship between an object’s distance and its recession velocity, a fundamental concept in cosmology. By analyzing spectral signatures within a galaxy’s light, astronomers precisely measure its redshift. This measurement calculates how long the light traveled to reach Earth, essentially looking back in time to its emission.
The James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) measures redshifts for faint, distant galaxies. Its ability to split light into component colors and identify spectral lines provides accurate distance measurements. These techniques help construct a timeline of the universe’s evolution, revealing when and where early structures formed.
The Farthest Light We Can See
While distant galaxies are the farthest individual objects we observe, the absolute farthest light originates from an earlier epoch: the Cosmic Microwave Background (CMB). Often described as the “afterglow” of the Big Bang, the CMB is pervasive radiation filling all space, not light from a specific object.
This ancient light was released when the universe was about 380,000 years old. At that time, the universe cooled enough for electrons to combine with atomic nuclei, forming neutral atoms. Before this, the universe was an opaque, hot plasma where light scattered. Once atoms formed, light traveled freely, and this “first light” has traveled across the cosmos since.
The initial radiation from this era stretched into microwaves due to the universe’s continuous expansion. Observing the CMB is like looking at the “surface of last scattering,” the edge of the observable universe in terms of light. It provides a snapshot of the universe in its infancy, supporting the Big Bang theory.
The Dynamic Universe and Our View
The concept of “farthest” is dynamic due to the universe’s ongoing expansion. While light from JADES-GS-z14-0 traveled about 13.5 billion years to reach us, the galaxy is now much farther away due to space expansion. This distinction between light-travel distance and current proper distance helps understand cosmic scales. For instance, JADES-GS-z13-0, whose light traveled 13.4 billion years, is now estimated at 33.6 billion light-years away.
Our ability to observe the universe is limited by the speed of light and its age, defining the observable universe. This spherical region around Earth is where light has had enough time to reach us. The universe itself is vastly larger than this observable portion, with its full extent unknown.
New generations of telescopes, like the James Webb Space Telescope, allow astronomers to peer further back in time and space, revealing previously undetectable objects. These advancements redefine observational boundaries. The dynamic nature of cosmic discovery means the “farthest thing” is a constantly evolving record, pushing our understanding of the universe’s origins and evolution.