How the James Webb Space Telescope is changing astronomy

Overview

The James Webb Space Telescope (JWST) is a highly advanced space observatory launched by NASA in December 2021, designed to enhance our understanding of the universe. With a primary mirror measuring 21.3 feet (6.5 meters) across, the JWST is the most powerful telescope ever sent into space, capable of detecting infrared light. The wavelength range covered by Webb's scientific instruments spans approximately 0.6 μm to 28 μm — from visible to mid-infrared light — compared to the Hubble Space Telescope, which observes at 0.1–2.5 microns. Webb has a segmented primary mirror that collects almost six times more light than the Hubble Space Telescope, and a five-layer sunshield that protects it from the infrared radiation of the Sun, Earth, and Moon. Unlike Hubble, it does not orbit Earth; instead, it orbits the Sun 1.5 million kilometers (1 million miles) away at what is called the second Lagrange point, or L2.

Probing the Cosmic Dawn

One of JWST's most transformative contributions has been its ability to observe the universe's earliest epochs. One of JWST's primary objectives is to study the universe's origin and evolution by detecting light from the first stars and galaxies formed approximately 180 million years after the Big Bang. Its infrared vision enables it to look further back in time than any previous telescope, providing insights into early galaxy formation, stellar birth, and the behavior of black holes.

Over the last two years, scientists have used the JWST to explore what astronomers refer to as "Cosmic Dawn" — the period in the first few hundred million years after the Big Bang when the first galaxies were born. These galaxies provide vital insight into the ways in which gas, stars, and black holes were changing when the universe was very young. The scale of these findings has stunned researchers: the first few years of JWST observations have revealed a significantly more vigorous early universe than anticipated from extrapolations of lower-redshift studies, with many findings challenging the canonical picture of galaxy formation and evolution.

Unexpected Galaxy Discoveries

JWST has repeatedly surprised astronomers with discoveries that challenge existing models. Back in December 2022 — less than six months after the JWST came online — the telescope revealed a new cosmic phenomenon: numerous small and mysterious red objects nicknamed "Little Red Dots," thought to be a new class of galaxy. Astronomers compiled a massive catalog of these objects, all dating back to the first 1.5 billion years after the Big Bang, finding that a large proportion appear to contain supermassive black holes that are actively growing. Physicist Dale Kocevski of Colby College remarked, "We're confounded by this new population of objects that Webb has found."

In another striking finding, astronomers using the James Webb Space Telescope spotted something that arguably should not exist: a massive galaxy, formed less than 2 billion years after the Big Bang, that appears to have no rotation at all — a trait usually seen only in much older, evolved galaxies. This challenges current theories that young galaxies should still be spinning from their formation.

Exoplanet Atmospheres and the Search for Life

The James Webb Space Telescope has ushered in a new era in exoplanet research. To learn about the diversity of exoplanets and their atmospheres, Webb is studying a range of worlds, from hot Jupiters to small rocky planets, deepening understanding of how planetary atmospheres form and evolve over time. Exciting discoveries of molecules such as methane on the exoplanet K2-18 further the discussion of potentially habitable worlds.

The largest and most complex space telescope ever launched, JWST is the result of an international collaboration including NASA, the European Space Agency, and the Canadian Space Agency. Its sensitivity continues to astonish scientists; as one astronomer noted, "We were so used to looking at noisy data with large error bars, where you can't really tell what you're looking at. With JWST data, often we're still blown away."

The Hubble Tension Crisis

JWST has also weighed in on one of cosmology's most pressing controversies. Once JWST started imaging the cosmos, it promptly began breaking existing models of the universe. It rapidly confirmed the Hubble tension — the discrepancy between the universe's expansion rates depending on where and what astronomers measure. In 2023, researchers used the more accurate JWST to confirm that, for the first few "rungs" of the cosmic distance ladder, their Hubble measurements were correct — meaning the tension with measurements derived from the early universe's cosmic microwave background is real, and not a consequence of measurement error. This has led some physicists to describe the situation not as a tension, but as a genuine crisis demanding new physics.

Broader Impact on Astronomy

JWST has made groundbreaking contributions to the study of exoplanet atmospheres by analyzing the chemical compositions of planets orbiting other stars, opening possibilities for identifying potentially habitable worlds and understanding planetary system formation, contributing to the broader search for life beyond Earth. JWST surpasses other telescopes mainly through its mirror size and infrared capability. Unlike Hubble, which is optimized for visible light, JWST's infrared sensitivity allows it to see through cosmic dust and detect the earliest galaxies and stellar events. By reaching where no telescope has gone before — both in distance and in wavelength — JWST is fundamentally rewriting the textbooks of modern astrophysics.