Webb Peers Through the Dust of Centaurus A, Revealing Millions of Stars and a Galactic Collision’s Hidden History
Featured image: Webb NIRCam and MIRI composite of Centaurus A (NGC 5128); credit: NASA, ESA, CSA, STScI
The James Webb Space Telescope has turned its infrared gaze on Centaurus A (NGC 5128), the nearest active galaxy to Earth at just 11 million light-years away, and delivered a view that no telescope has ever produced before. Webb’s NIRCam and MIRI instruments cut through the dense dust lanes that have obscured the galaxy’s chaotic center since its discovery 200 years ago, revealing millions of individual stars and an S-shaped feature of unknown origin.
> “No single telescope tells the whole story. Discoveries build over time and new observatories expand on the foundations laid by earlier missions,” said Shawn Domagal-Goldman, Division Director for Astrophysics at NASA Headquarters. “Webb represents the most powerful step forward yet, opening a window into wavelengths and details never before accessible.”
A Galaxy Born from Collision
Centaurus A is not a typical elliptical galaxy. Roughly 2 billion years ago, it merged with a spiral galaxy, and that collision left scars visible across the electromagnetic spectrum. A warped parallelogram-shaped dust lane bisects the galactic center. Uniquely among elliptical galaxies, Cen A sprouted spiral arms after the merger. And at its heart sits a supermassive black hole of roughly 100 million solar masses, actively feeding and launching jets of relativistic plasma visible across the radio spectrum.
Hubble’s visible-light cameras could only hint at what lay behind the dust. Spitzer revealed warm dust but could not resolve individual stars. Webb’s near-infrared and mid-infrared vision changes that completely.
“With Webb’s view of Centaurus A, it becomes a case of galactic archaeology,” NASA said in its release marking Webb’s fourth science anniversary on July 6, 2026.
The S-Shaped Mystery
The most striking feature in Webb’s mid-infrared image is a glowing S-shaped structure near the galaxy’s core. Its origin is unknown, and NASA scientists have openly listed the questions it raises: “What created this shape? How does the black hole influence it? Is it influenced by merger-induced star formation?”
The structure appears prominently in MIRI’s view and may trace ionized gas or dust sculpted by the active galactic nucleus. The team behind the observations has not yet published a dedicated analysis, but the images were released as part of Webb’s anniversary portfolio.
Resolving the Unresolvable
Before Webb, telescopes could see Centaurus A’s dust lane but not the stars within it. The dust absorbs visible light, creating the dark band that has defined the galaxy’s appearance in every Hubble image. Webb’s infrared instruments see through that dust, detecting the heat of stars that have been hidden since the galaxy’s discovery by James Dunlop on August 4, 1826.
The glowing red points in the MIRI image represent dust-rich stars and stellar nurseries, the raw ingredients for future star formation. By cataloging these stars, astronomers can reconstruct a timeline of the galaxy’s life: ancient star formation, a slowdown, the collision-triggered starburst, and post-merger star formation.
Black Hole Feedback in Action
A companion spectroscopic study published in Astronomy & Astrophysics (A&A 699, A334, July 2025) using Webb’s MIRI MRS (Medium-Resolution Spectrometer) as part of the MICONIC GTO program has already begun unpicking the black hole’s influence. The study detected a fast ionized gas outflow confined within the central 6 parsecs, with velocities ranging from +1,000 to -1,400 kilometers per second.
The outflow is likely jet-driven. Cen A’s relativistic jet, traveling at roughly half the speed of light, expands into the interstellar medium and drives a bubble that pushes ionized gas outward at a rate of 1.6 to 2.9 solar masses per year. The geometry matters: because the jet is perpendicular to the galaxy’s disk, it has poor mechanical coupling with the molecular gas, which explains why no fast molecular hydrogen outflow was detected.
This makes Centaurus A a rare nearby laboratory for studying how supermassive black holes both trigger and suppress star formation, a process that shapes the evolution of all large galaxies.
Why It Matters
Centaurus A is the second-brightest extragalactic radio source in the sky, after Cygnus A. It is a radio galaxy, an active galactic nucleus, a post-merger system, and a starburst environment all in one object. Webb’s ability to resolve individual stars across 11 million light-years, in a galaxy where every previous telescope saw only a dust-obscured blur, represents a fundamental increase in observational power.
The full suite of Webb images and the companion spectroscopic data are available through the Space Telescope Science Institute. As NASA’s Domagal-Goldman noted, discoveries build over time. Centaurus A’s secrets are only beginning to emerge.