Gas falls onto a neutron star — the ultra-dense remnant of an exploded star. This gas accumulates at the magnetic poles and forms a mountain. But a mountain on a neutron star is not like one on Earth: it is held not by rock but by magnetic field lines, like iron filings on a magnet.
When there is too much gas, the mountain begins to break apart. Turbulent flows inside it mix the material, and it seeps across the magnetic field lines. Previously, it was thought this would destroy the mountain. But calculations showed the opposite: the gas flow itself quenches the turbulence and preserves the mountain. It's like a sand dune that shifts shape in the wind but doesn't disappear.
Unless destroyed by electrical resistance, the mountain can survive for millions of years. That means many neutron stars have such invisible mountains. They are like quiet beacons sending signals across the universe.
A mountain on a neutron star just a few centimeters high would weigh as much as all the mountains on Earth combined.