It's a process called 'cavitation', and it works like this:
If a high frequency sound wave - or a fast moving object - goes through a liquid it can cause the liquid to break into bubbles of vapour. When these bubbles collapse their walls rush inwards with incredible speed, rapidly crushing the vapour inside and heating it to tens of thousands of degrees.
Hotter than the surface of the Sun in fact.
Yep, hotter than that. But a bit smaller.
But, as hot as that is, the tiny flashes of light the bubbles give out are hard to explain - the bubbles collapse is violent, but only across a tiny, tiny, volume. It shouldn't glow visibly!
Explaining what the glow is has led to some wild explanations - and one is that the bubbles might have miniature nuclear explosions inside of them....