Thin Disks of Galaxies Already Existed in the Young Universe ⚡ экспресс
Disks of spiral galaxies contain both a thin and a thicker component, but when did these thick disks form? Using a new method on JWST images, scientists measured the true thickness of ancient galaxies, avoiding past errors from tilted views. They found that 11–12 billion years ago, galaxies had thin disks with scale heights around 0.25 kpc, much like the Milky Way today—about 1.6 times flatter than earlier estimates. Surprisingly, any thick disk present must be very faint, suggesting thick disks are built gradually over billions of years.
The James Webb Space Telescope peered 11 billion years back in time and spotted galaxies turned edge-on toward us. To measure their thickness, scientists devised a clever method: they calculated it the same way you'd measure the thickness of a slightly tilted pancake, not a perfectly flat one. Previous estimates were imprecise because they assumed an ideal angle.
It turns out those ancient stellar pancakes are nearly as thin as our Milky Way's disk: their diameter is about eight times their thickness. This discovery flips the script: thin disks aren't the end result of long evolution, but the natural state of young galaxies in an era when the Universe was expanding rapidly. And what's more, no noticeable thick layer was found in them.
So, the thick disks we see in nearby galaxies piled on later—probably when their stellar populations got "shaken up" by collisions. Here's an unexpected twist: our own Milky Way was just as slim in its youth; its current bulk is a scar of a turbulent history.
🎯 If you shrunk the disk of our Milky Way to the size of a vinyl record, its thickness would be comparable to a sheet of paper.