Scientists say they have discovered the fastest possible speed of sound.
Researchers found soundwaves travelled at 36km per second in solid atomic hydrogen.
That is about twice the speed at which they can travel through diamond - the hardest known material in the world.
Image: You can hear a train through the tracks more quickly than through the air
Until now, it was not known whether there was an upper speed limit, either through solids or liquids.
Soundwaves go at different speeds, depending on what they are travelling through.
They pass through solids more quickly than through liquids or gas - which is why a train can be heard sooner through the tracks than through the air.
Scientists tested a wide range of materials, and found the speed of sound in solid atomic hydrogen is close to the theoretical fundamental limit.
The research, published in the journal Science Advances, came from a collaboration between Queen Mary University of London, the University of Cambridge and the Institute for High Pressure Physics in Moscow, Russia.
The study of soundwaves has important scientific applications.
Professor Chris Pickard, Professor of Materials Science at the University of Cambridge, said: "Seismologists use soundwaves initiated by earthquakes deep in the Earth interior to understand the nature of seismic events and the properties of Earth composition.
"They're also of interest to materials scientists because soundwaves are related to important elastic properties including the ability to resist stress."
Professor Kostya Trachenko, Professor of Physics at Queen Mary University of London, said: "We believe the findings of this study could have further scientific applications by helping us to find and understand limits of different properties such as viscosity and thermal conductivity relevant for high-temperature superconductivity, quark-gluon plasma and even black hole physics."