In the last post I talked about The Big Bang – a cataclysmic event 13.8 billion years ago which resulted in all the matter we see [and don’t see] in the Universe. But how did this lead to us and all the life on this remarkable planet called earth?
The surprising answer is that every atom in our bodies, all the elements that form everything we see and touch were produced in the incredible furnaces of dying stars! And those same atoms and elements will be returned to the cosmos when our star, the Sun, eventually collapses and explodes – but not for 7 billion years when it will run out of fuel.
So let us consider the life of a star because they have been birthing and dying since about a billion years after the Big Bang and we are currently waiting to see the death throes of a nearby star – but more on that later in this post.
Stars are formed in a process where dense regions within molecular clouds in interstellar space, normally called stellar nurseries, collapse into spheres of plasma to form stars. They comprise mostly hydrogen with some helium. Hydrogen is the main fuel source for all stars including our sun. Temperatures and pressures are so high at the centre of stars that the hydrogen is converted into helium with the release of energy in the form of radiation. We see this as light and heat but there are many other kinds of radiation [mostly dangerous] bombarding our planet.
The sun burns a staggering 600 million tonnes of hydrogen every second! But do not worry because even at this rate our Sun will last for 7 billion years. But we only have the elements hydrogen and helium [the lightest] at this stage so where do our building blocks for life eg carbon, oxygen, nitrogen etc. come from? The answer lies in the death of stars – when the fuel eventually runs out the star firstly expands into a red giant and then collapses in on itself producing one the most spectacular events in the solar system – a Supernova.
Supernova occur on average 3 times per year in the Milky Way but the last observed was in 1604 – Kepler’s Supernova. So stars are dying with regular frequency in ours and all the galaxies. But why is this critical to us? When a massive star collapses the temperatures and pressures at the centre dramatically rise causing fusion of hydrogen and helium atoms to form heavier elements. Thus carbon, oxygen, nitrogen [the lighter elements] are produced in abundance with smaller amounts of heavier elements [silicon, iron] and trace quantities of the really heavy elements [the hardest to make] eg gold. But the whole periodic table of elements [98 naturally occurring] is produced. Then the core explodes in the most dramatic event [other than the Big Bang] and all this newly produced matter is flung out into interstellar space where it is carried to other stars and their orbiting planetary systems.
Thus the building blocks for life on Earth arrived as the residue of dying stars – our origins are truly Stardust!
However getting the elements to a planet is one thing. Building them into life needs a very special set of circumstances which I will talk about in the next post.
ps – astronomers are eagerly awaiting the next visible Supernova and the most likely candidate is the 2nd brightest star in Orion and visible to the naked eye – Betelgeuse – a red supergiant. The best estimates for this to happen is within the next million years! So do not get your hopes up within our lifetimes. However it may have already blown up. It is about 640 light years from Earth so if it happened now the evidence would not be seen until 2653 – I wonder what our world would look like then and would we still be about to see it? Or maybe we will have already colonised other stars – we will have to eventually!
So fasten seat belts and take a journey to the star, Seren – what will you discover?