Thin Disks of Galaxies Already Existed in the Young Universe ⚡ экспресс
The thickness of galactic disks constrains formation scenarios: whether thick components arise from early turbulence or later dynamical heating. A new methodology for edge-on galaxies fits a full 3D model, correcting for slight inclinations that biased previous single-disc fits upward. Applied to JWST data of 10^9–10^10 M⊙ galaxies at redshifts 1–3, it yields median scale height z₀ = 0.25 ± 0.14 kpc and axial ratio h_r/z₀ = 8.4 ± 3.7 — consistent with the Milky Way’s thin disk and ~1.6× thinner than local estimates. Thus, thin disks were already in place at z ~ 3. A hypothetical thick disk contributing 10% of the thin disk’s luminosity would be detected, implying any thick component must be fainter, supporting a scenario where thick disks form progressively through dynamical heating at z < 1.
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.