2015-03-27 BBC:星光七纪元-20（在线收听）

 Actually, Arcturus is an omen of something far worse than the bad weather, a portended drama more intense than any of what you could imagine. When our own sun eventually becomes a red giant in 5 billion years time, it will turn into a destroyer rather than a protector of worlds. Doctor Robin Catchpole, has devoted his middle years to studying these devouring beast of the light. Their story starts the day the hydrogen in their core runs out. Most of the stars’ life, it spins  fusing hydrogen into helium. And this of course provides the pressure that resists the force of gravity. When the hydrogen runs out in the core we just got the helium. Then there is no source of energy, so the core starts to collapse. And as it collapses under the force of gravity, it heats up. And the temperature becomes high enough to start nuclear fusion reactions in the shell around the core. So we have what we call shell hydrogen burning. Fusion has stopped in the core. It's still hot, but it's dead. The star is now fundamentally different form our twinkling sun. The light we have seen is still being generated by nuclear fusion, but it's happening in a ring of hydrogen that surrounds the core instead.