After an altogether far-too-long hiatus due to Kiwipycon, the upcoming ‘Official Sciblogs Podcast’, a series of videoprofiles of MacDiarmid Institute Alumni, the 2011 NZ Datamixandmash competition, the Tell Us a Story Competition at Victoria University and gorgeous clear skies last night – I’ll get back to the story of stellar evolution! (You can find part 1 here)
When we last left our forming stars, their parent nebulae had just collapsed under gravity providing enough energy to ‘ignite’ the process of nuclear fusion that will fuel the stars for the rest of their lives. We could feasibly skip the details of this process by saying “the heat generated by this gravitational collapse allows the individual Hydrogen atoms to smash into each other with enough energy to fuse, forming Helium and producing large amounts of energy as light”. Certainly sounds reasonable enough.
But there’s a problem. Usually, when we heat things, they stick together less (think about butter melting when you heat it) – so why would the hydrogen atoms stick together MORE when they start moving faster? And furthermore WHERE DOES THE ENERGY COME FROM??!! It’s true that things emit more light the more you heat them (a process known as blackbody radiation) – but to emit as much light as stars do for billions of years these hydrogen atoms would have to be at temperatures much higher than what we actually see in stars. Essentially, there’s not enough energy in the movement of these atoms to produce the light that we see – so what’s going on!
Confused? Don’t worry. So was the entire scientific community for a number of years after making these realizations and to understand the process we need to delve into a little into bizarre quantum physics, and Einstein’s famous equation: E=mc².
I’ll discuss the quantum detail in an upcoming nanotech post, as it certainly doesn’t just occur in the sun – but the energy problem can be answered simply. That equation above describes the equivalence between mass and energy – it says that under the right conditions they can be interchanged, but that’s certainly not what we see on a daily basis! Can you imagine being the middle of a conversation with a person, and then having them spontaneously erupt into a massive wave of energy? And when I say massive – that is an understatement, and a huge one at that. The rest of Einstein’s formula is that c² term. That’s the speed of light squared, and light is quick. In fact, it’s the fastest anything can travel – 300 000 000 meters per second. So the formulae above can be simply stated thusly:
“There’s a LOT of energy in mass.”
By example – if you converted all of an average person’s mass into energy, you would end up with more than the combined total of every nuclear weapon every detonated on earth. A LOT of energy.
And that’s precisely what happens in stars. When two Hydrogen atoms fuse, they produce Helium – but Helium’s mass is just slightly less than that of two individual Hydrogen atoms; the extra mass has been converted to energy during the fusion process. That’s why stars are so bright and so long lived – they burn mass itself and convert it into energy. Take a moment to digest that statement – and if you’re out enjoying the sun this weekend, give thanks that the sun is as far away as it is.
I’m quite fond of my hydrogen atoms personally, and don’t relish the though of any part of me being turned into energy – no matter how beautiful the result may be!