The Bicycle Dynamo in Space: How Collapsar Jets Are Born ⚡ экспресс
For the first time, three-dimensional general relativistic magnetohydrodynamic simulations of collapsars have been performed with an initial toroidal magnetic field taken from pre-collapse stellar models. Once dynamically significant, the toroidal field triggers a dynamo that generates coherent poloidal magnetic loops at distances of around 100 gravitational radii. These loops are then carried inward through the disk, sometimes tilting out of the equatorial plane, threading the black hole, and producing highly variable, precessing relativistic jets on timescales of seconds. Jet onset depends on the initial field and the plasma circularization radius. Despite high variability and misalignment with the black hole spin axis, the jets consistently deliver power exceeding 10^50 erg/s, matching that of long gamma-ray bursts. Stochastic magnetic flux reversals are observed, leading to “striped” jets that may be imprinted in the light curves. The results demonstrate that accretion disk dynamos are a universal mechanism for launching jets in collapsars across a wide range of progenitor properties.
A massive star collapses, and a black hole is born, surrounded by a disk of incandescent plasma. For narrow jets to burst out of this disk, an ordered magnetic field is needed. But inside the star, it's tangled. Supercomputer calculations showed: the disk works like a bicycle dynamo hub—rotation itself brings order to the magnetic field.
At first, the field twists into rings, and then, like a self-exciting dynamo, it generates giant magnetic loops. They are pulled toward the hole and shoot out oscillating jets at nearly the speed of light. This mechanism doesn't need an inherited field from a proto-neutron star—it's universal for various collapsars, one of the types of supernovae.
An unexpected result: the jets turned out to be striped—the magnetic field in them periodically flips. These stripes will be imprinted in the brightness curve of the gamma-ray burst, becoming the signature of the dynamo. So an unremarkable effect turned out to be a simple recipe for the most powerful explosions in the universe. Even Kip Thorne pondered how black holes launch jets, and Fritz Zwicky was the first to suggest that neutron stars are born in supernova explosions—now new work ties these phenomena together.
🎯 Earth's magnetic field is also generated by a dynamo effect in the liquid core—but there it operates for billions of years, while in a collapsar the entire process takes seconds.
🎬 If sci-fi writers imagine starships with miracle engines, nature has already built its own accelerators—collapsar jets, ejecting matter at nearly the speed of light.