Webb Unveils Millions of Stars in Centaurus A, Resolving a Galaxy Shaped by Cosmic Collision
Featured image: [Webb NIRCam and MIRI composite image of Centaurus A (NGC 5128), showing millions of individually resolved stars and the galaxy’s distinctive dust lane; credit: NASA/ESA/CSA/STScI]
The James Webb Space Telescope has resolved millions of individual stars in the dusty core of Centaurus A (NGC 5128), the closest active galaxy to Earth, the European Space Agency announced July 6. The images, released to mark Webb’s fourth anniversary of science operations, offer an unprecedented view of a galaxy still bearing the scars of a major collision roughly 2 billion years ago.
Centaurus A, located 11 million light-years away in the constellation Centaurus, is the most prominent radio galaxy in the sky. Its peculiar shape and dark dust lanes have long marked it as the product of a galactic merger. But visible-light observations from the Hubble Space Telescope could not penetrate the thick dust obscuring the core. Webb’s near-infrared camera (NIRCam) and mid-infrared instrument (MIRI) cut through that veil, revealing stellar populations never before seen individually in this region.
“Webb represents the most powerful step forward yet, opening a window into wavelengths and details never before accessible,” said Shawn Domagal-Goldman, Astrophysics Division Director at NASA Headquarters.
Galactic archaeology star by star
The infrared observations enable a kind of galactic archaeology : reconstructing Centaurus A’s timeline by analyzing the types, ages, and distribution of its stars. NIRCam resolved stars individually all the way to the galaxy’s core, distinguishing old populations formed before the merger from younger stars born during the collision and its aftermath.
MIRI’s mid-infrared view revealed a striking gray-white parallelogram-shaped dust band cutting across the galaxy’s center. Delicate loops and wispy ribbons of pink and lavender arc above and below the core in an S-shaped configuration. The origin of this feature is unknown; it may be linked to activity from the supermassive black hole or to merger-induced star formation.
Glowing red points in the images are identified as dust-rich stars or stellar nurseries : aging stars shedding material or new stars forming from gas stirred up by the merger.
The black hole connection
The supermassive black hole at Centaurus A’s center, estimated at roughly 100 million solar masses, plays a dual role in shaping the galaxy. Spectroscopic data from Webb reveals fast-moving ionized gas flowing outward, likely driven by the black hole, along with warmer molecular hydrogen in a warped rotating disk near the center.
“Centaurus A offers a rare, nearby view of this cosmic interplay,” the ESA stated, referring to the co-evolution of galaxies and their central black holes. The black hole can both trigger star formation : by compressing gas clouds : and limit it, by pushing material out of the galaxy.
A milestone for Webb’s fourth year
The Centaurus A observations are part of a broader set of results from Webb’s fourth year of operations. Other highlights include a planet candidate orbiting Alpha Centauri just 4 light-years away, the earliest known supernova at 730 million years after the Big Bang, and the most comprehensive view of Saturn combining Webb and Hubble.
Webb launched in December 2021 and began science operations in mid-2022. Europe’s contributions include the Ariane 5 launch vehicle, the NIRSpec spectrograph, and half of the MIRI instrument, built by a consortium led by European institutes in partnership with NASA’s Jet Propulsion Laboratory and the University of Arizona.