2015-01-30 BBC:星光七纪元-5（在线收听）

Many regions within these clouds can stay like that for ever for millions of years until something happens, a trigger and then a star forms.The trigger for such a monumental event doesn't have to be much, two clouds conbine as they pass, or a distant cosmic event can send a shockwave, just something to give the cloud a squeeze.

All you need is a little bit of pressure to allow the gas to be dense enough for gravity to take over and collapse to start.

The particles of dust and gas that had been quietly floating in space now start being pulled together, gravitational attraction draws them towards each other, faster and faster.

As the collapse continue to happen, the gas and the dust will fall into the center and they will become denser and denser, and the center of the cloud will become hotter and hotter.

The laws of nature mean that when matter gets compressed, it heats up, over millions of years, the protostar grows, increasing the pressure and heat in its core, until finally it reaches a critical temperature.

About 15 million degrees and a fundamental process will start in the core of the embryonic star.

Almost in a flash, the core of the star like our own sun's once did dazzlingly lights up.