A hair dryer aimed at a block of ice strips vapor and droplets from its surface, and the ice slowly melts. The wind from the center of our Galaxy works in much the same way: it picks up cold gas clouds and carries them away, heating and shredding them along the way.
Astronomers decided to systematically search this flow for molecules, the coldest and densest form of gas, for the first time. They pointed the APEX telescope in Chile's Atacama Desert at 19 patches of sky where fast-moving clouds of atomic hydrogen had previously been seen. In 16 of them, they found traces of carbon monoxide (CO)—a reliable sign of molecular clouds. In total, they detected more than 200 individual clumps.
These clumps are small: a few light-years across, with masses ranging from a few to hundreds of solar masses. But the key thing is that they are highly turbulent. Internal gas velocities reach several kilometers per second, which is unusually high for such small clouds. Nearly 90% of the clumps are not held together by their own gravity: they would fly apart unless squeezed by the external pressure of the hot gas.
Interestingly, in none of the six clouds located more than a thousand light-years from the center were molecules found. Apparently, during their flight, about three million years, all the molecular gas gets destroyed. First it breaks into individual atoms, then into ionized plasma.
In this way, the hot wind recycles the Galaxy's cold building material, preventing it from assembling into new stars. The ice melts, leaving only vapor behind.
Carbon monoxide (CO) is the second most abundant molecule in the interstellar medium after hydrogen. Astronomers use it as a tracer of cold molecular gas because it glows in the radio range even at temperatures just 10–20 degrees above absolute zero.
In Stanisław Lem's novel Solaris, the ocean creates giant structures that scientists cannot explain. The galactic wind also gives rise to strange clouds, but their shape and fate follow simple laws of physics.