The Hourglass of an Ancient Galaxy: JWST Spots Maturity That Arrived Too Soon
Original: "Bar-driven secular evolution largely complete in a disk galaxy 7.6 billion years ago"
The James Webb Space Telescope has spotted a distant galaxy, UDS 12999, where already 7.6 billion years ago, a bar, nuclear disk, and X-shaped bulge had formed—hallmarks of a finished evolution that, it was thought, takes far longer.
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7.6 billion years ago, galaxy UDS 12999 was already flaunting a mature X-shaped bulge, as if its evolution had been run through a giant hourglass. The bar, like a neck, accelerated the inflow of matter, and in just 3.8–5.4 billion years it assembled the mass of the Milky Way. Now JWST will search for such “hourglasses” at even greater depths. The Universe is maturing faster than we thought—we’ll have to rewrite the chronology of galactic coming-of-age.
🎯 Stars in the X-shaped bulge move along orbits resembling an hourglass: they rise and fall, creating vertical streams that give the structure its “X” shape when seen edge-on.
\tau_\text{disk} + \tau_\text{bar} + \tau_\text{X} < 3.8-5.4 \text{ Gyr}
The sum of the formation times of the disk, bar, and X-bulge is bounded above by a period of 3.8 to 5.4 billion years.