The Mature Bar: How a Galaxy 7.6 Billion Years Ago Outpaced the Universe ✦
Using the James Webb Space Telescope, astronomers studied a galaxy at redshift 0.92 (its light traveled 7.6 billion years) and found a fully developed structure: an X-shaped bulge (a thickening at the center), a nuclear stellar disk, and an extended disk. Such geometry and bar size are indistinguishable from those of modern spiral galaxies like the Milky Way. This means that a key evolutionary stage—the formation of the bar and bulge—was completed when the universe was less than half its current age.
The potter’s wheel of the cosmos spins faster than we imagined. Look at galaxy UDS 12999: its light traveled 7.6 billion years, but James Webb discerned a perfectly cast X-shaped bulge already at its center. This is no mere pattern—it’s the fingerprint of a mighty stellar bar that, like a potter, stretched and molded the central region. The disk is still raw clay, while the bar is already a master, leaving its trademark monogram.
Back then, Edwin Hubble spotted bars in many spirals, and Vera Rubin proved their rotation is governed by unseen mass. Now spectroscopy and photometry with JWST have measured the redshift to five decimal places (z=0.92331) and reconstructed the star formation history. It turns out the galaxy amassed half its colossal mass (7.7×10^10 M☉) in the first billion years after the Big Bang, then the pace fizzled. Star birth in the X-bulge ceased 270 million years ago, while the disk kept smoldering like a cooling forge.
The timeline jolts us: from the formation of a cold disk to the emergence of a mature X-structure, no more than 3.8–5.4 billion years passed. This forces a shake-up of numerical simulations—in them, bars usually “ripen” only by z~0.5, when the Universe is twice as old. UDS 12999 shows that gravity can drive evolution at a gallop where we expected a stately stroll.
The discovery stitches together two worlds: mature systems at high redshifts in telescopes, and theoretical models that must now reproduce early X-bulges. Soon, Euclid and ELT will mount a deliberate hunt for these “early bloomers,” and their kinematics will reveal how durable bars are in the young Universe. The cosmic potter left us his creations—and they are older than we ever imagined. And perhaps the most astonishing thing isn’t that they exist, but how early the craftsman set to work.
🎯 Our own Milky Way also has an X-shaped bulge, discovered by the infrared telescope WISE; its formation likely wrapped up around 8 billion years ago.