Space gold! (Is not most exciting part of this story)
- 7 August 2013
- From the section Coventry & Warwickshire
What could be more exciting than tonnes of space gold being created in a violent cosmological explosion?
Well for astronomers, of course, it's actually the explosion rather than the sparkly element that's the focus of attention. But we're not astronomers, so let's focus on the gold first.
One of the nicest astronomy apercus is that we're all made of "star stuff". So there's the Big Bang and then the Universe forms and it's full of hydrogen and helium.
After that we need to wait for stars to start to form and that provides a place for other heavier elements to be created.
Inside a star you get nucleosynthesis and that means you create other elements, as helium turns into beryllium and carbon and eventually other heavy elements, up to and including iron.
Then stars go supernova, which creates even heavier elements like nickel, and as a bonus the explosion spreads all these exciting new atoms right across space.
Look around and everything you see is made of elements created in stars, which is cool but it begs the question, what about heavier elements, like gold for example?
Well for that you need a particular type of cosmic explosion.
According to researchers at the University of Warwick, up to 90% of the gold in the Universe is produced in a kilonova, when two neutron stars locked in a death-spiral collapse into each other and explode. That produces conditions extreme enough to make perhaps all the heavier elements including gold.
To be honest you'd be hard-pressed to "mine" an exploding "kilonova" - but I'm never looking at my wedding ring in the same way.
For the astronomers at Warwick, though, it's the kilonova itself that's exciting and they were very pleased to observe one earlier this year.
In the scheme of things, these are very rare events - just think about what is involved.
First of all you need a pair of neutron stars, that is what's left of a sun after it supernovas.
Only about 5% of neutron stars have a twin. The two neutron stars then slowly spiral around each other and eventually collapse and explode.
In a galaxy you may not get one for millions of years - what are the odds of seeing one at all from Earth?
Astronomical 'smoking gun'
Well fortunately for us astronomers are good at looking and space is big. Like really big.
So we can expect to track about one kilonova a month. Astronomers look out for the massive, gamma ray flashes exploding objects give out.
These are tracked by the Swift satellite which narrows down the part of the sky the gamma rays come from.
Then astronomers gazump all the other telescopes on Earth and in space - whatever experiments the big telescopes in Chile or the Hubble are up to, they are overridden and instead are turned to face the explosion and track it as it fades away.
All that information arrives back at Warwick and it was during some of the analysis the astronomers discovered something really interesting.
One particular cosmic explosion died away, as you'd expect, but then it suddenly "re-brightened" before fading away again.
For the astronomers that's a "smoking gun" - it means that kilonova was definitely caused by a pair of neutron stars and also that gold and other heavier elements were produced in the explosion.
It perfectly matched a theoretical prediction for this sort of event that had been made just a month earlier.
So as you can see, "space gold" is probably the least interesting part of this amazing astronomical discovery. The full letter to Nature is here.
Also a note for astronomers: Calling something between a nova and a supernova a "kilonova" may make scientific sense - but it just overexcites some journalists who think you are talking about a "killer nova".