Gas Jumps Over the Ring express
A river flows toward a whirlpool, but a dam with a notch blocks the way. Most water piles up before the dam, but some, gaining height, leaps over it and falls straight into the funnel. So it is with gas in a galaxy: it streams toward the center but hits a ring of stars and gas, like a dam. Usually, everything stops there, swirling into a dense vortex.
But in the three-dimensional model built by scientists, some gas behaves differently. It rises above the galaxy's plane by about a hundred parsecs (roughly 300 light-years) and flies over the ring. For this to happen, the gas must not only jump high but also lose some of its rotation. Then it falls inward, toward the very center — where the supermassive black hole sits.
This leap is not chaotic: the gas that reaches the center moves along a narrow corridor defined by the ring's thickness. Most of the gas still remains in the ring and gives birth to new stars there. But the fraction that jumps over is enough to feed the black hole and explain why disks around it are often tilted relative to the galaxy.
Original abstract
as written by the authors arXiv:2604.17955
Gas delivery to galactic centers powers nuclear starbursts and active galactic nuclei (AGNs), yet bar-driven inflow is generally expected to stall in a nuclear ring a few hundred parsecs across. Using three-dimensional Lagrangian hydrodynamic simulations in a fixed barred potential, we identify a bypass channel in which a fraction of the inflowing gas acquires vertical momentum, vaults across the ring, and reaches the inner few tens of parsecs. This pathway is absent in two-dimensional calculations, which instead predict long-lived stagnation at the ring. We find that the circumnuclear material within $$\sim 50$$ pc originates from gas initially located outside the ring ($$\gtrsim 300$$ pc), rather than from secondary inflow out of the ring itself. Successful delivery requires both a sufficiently large vertical excursion, $$|z| \sim 100$$ pc before encountering the ring, and substantial loss of azimuthal angular momentum $$L_z$$. The resulting inflow is organized rather than chaotic: center-reaching trajectories are confined to a limited spatial region set by the scale height of the ring gas. Most bar-driven gas still accumulates near the resonance and fuels star formation in the nuclear ring, but the vaulting stream selects a modest yet sufficient fraction that penetrates to the circumnuclear disk. These results suggest that intrinsically three-dimensional gas motions help link nuclear starbursts, AGN fueling, and the frequent misalignment of nuclear disks with respect to their host galaxies.
The height the gas reaches before its leap is about 100 parsecs. That's roughly 300 light-years, or three times the distance from the Sun to the nearest star.