Students and enthusiasts attending a recording for BBC Radio 4 have probably seen a new state of matter only recently discovered, an expert says.

The state of matter is a plasma (ionised gas) like those in nuclear fusion tests, but at higher densities.

And far from needing hundred-million-pound apparatus, the conditions can be achieved in a simple glass tube containing a routine liquid.

The professor behind the demonstration says it can be achieved for a mere £10.

The audience were attending a demonstration lecture by chemist Professor Andrea Sella being recorded at University College London for Spooklights on Radio 4.

During the lecture, Professor Sella demonstrated a phenomenon called sonoluminescence - flashes of light created by collapsing bubbles in a fluid. The flashes are extraordinarily faint, but in the darkened auditorium, those attending could see the evanescent sparks quite clearly.

As the name suggests, sonoluminescence is traditionally created by intense sound waves - rapid pressure oscillations - focused into a liquid. In the low-pressure regions of the sound waves, fluid is ripped apart to create tiny bubbles, the source of the light.

Professor Sella's demonstration is far simpler, involving a simple sealed glass tube part filled with phosphoric acid and traces of the inert gas xenon. Then all that's needed is a gentle shaking of the tube. As the acid hits the tube's bottom, there's a distinct metallic clink, as if a heavy ball bearing is striking the glass wall.