The farthest galaxy from Earth is a moving target, tied directly to the fundamental physics of the cosmos. Because light travels at a finite speed, observing distant objects is equivalent to looking backward in time. The expansion of the universe continuously stretches the space light travels through, complicating the measurement of what “farthest” truly means. Therefore, the distance to these ancient objects is not a simple measure of miles, but a calculation based on how much the universe has expanded since their light began its journey.
The Current Farthest Galaxy
The current record for the most distant spectroscopically confirmed galaxy belongs to MoM-z14. This galaxy was confirmed using the James Webb Space Telescope (JWST) as part of the “Mirage or Miracle” (MoM) survey. Its extreme distance is quantified by its redshift value, denoted by the letter \(z\). MoM-z14 holds a confirmed redshift of \(z=14.44\), placing it as the most distant known galaxy at the time of its confirmation.
This high redshift means we are observing the galaxy as it existed less than 280 million years after the Big Bang. The record for the farthest galaxy is constantly being broken as new instruments, particularly JWST, push the limits of detection. The “farthest” designation is defined by the highest spectroscopically confirmed redshift, which corresponds precisely to the greatest lookback time.
Understanding Redshift and Cosmic Expansion
The primary method astronomers use to measure these cosmic distances is by analyzing cosmological redshift. This phenomenon occurs when light from a distant source is stretched to longer, redder wavelengths as the universe expands during the light’s journey. The value \(z\) represents the fractional increase in the wavelength of the galaxy’s light. A higher redshift number indicates that the light has been stretched more, signaling a greater distance and an earlier time in cosmic history.
It is helpful to distinguish this from the familiar Doppler effect, which describes the shift caused by an object moving through space. Cosmological redshift, by contrast, is caused by the expansion of space itself between the galaxy and the observer. Imagine a light wave traveling along a piece of stretching fabric; the wave itself is stretched as the fabric expands. Because the universe expands uniformly, the measured redshift provides a reliable way to calculate the total expansion that occurred during the light’s travel time.
Looking Back to the Cosmic Dawn
The observation of a galaxy like MoM-z14 is significant because it provides a direct view into the earliest moments of cosmic history. This era, known as the Cosmic Dawn, is the period when the first stars and galaxies began to form out of primordial hydrogen and helium gas. The light from these galaxies reveals the state of the universe when it was only about two percent of its current age. Studying these objects helps researchers understand how the first structures arose from the matter distributed after the Big Bang.
The existence of a galaxy this massive and luminous so early challenges existing theories of galaxy formation. The brightness of MoM-z14 suggests that star formation was highly efficient in the early universe. These early galaxies were also responsible for ending the “Dark Ages,” a period when the universe was filled with opaque, neutral hydrogen gas. The intense radiation from these first stars and galaxies ionized this gas, a process called the Epoch of Reionization, making the universe transparent to light.
The Technology Required for Detection
Detecting a galaxy with a redshift of \(z=14.44\) requires specialized instruments designed to capture the extremely stretched light. The light emitted by MoM-z14 was originally in the visible and ultraviolet spectrum, but cosmic expansion has shifted it far into the infrared region. The James Webb Space Telescope (JWST) was engineered specifically to observe this infrared light, which is invisible to the human eye and previous telescopes like Hubble.
JWST uses instruments like the Near-Infrared Spectrograph (NIRSpec) and the Near-Infrared Camera (NIRCam) to capture and analyze this faint, redshifted radiation. Spectroscopic confirmation, achieved by NIRSpec, is the definitive method for calculating the precise redshift. Astronomers also rely on gravitational lensing, where the gravity of a massive foreground galaxy acts as a magnifying glass. This technique amplifies the faint light from distant objects, making them bright enough for JWST to observe in detail.