The Winter games are over and a disproportionate number of Norwegians and Canadians are homeward bound with precious metals. Two of you recently won gold medals - one in physics, the other in computer science and another stands an excellent chance of winning gold in beach volleyball in the Tokyo games two years from now. But a simple question: where does gold come from?
Until recently gold's origin was the stuff of speculation. Nuclear fusion in stars produces elements past helium.. Hydrogen burns to helium, helium burns to carbon and so on. But the process gets stuck at iron and is unable to produce anything heavier. To get there you need different mechanisms.
Supernovas came to mind and do some of the work, but getting to very heavy elements - the precious metals for example - is difficult . Something wildly powerful is needed. Kilonovas - the strength of a thousand novas - were theoretically possible if two neutron stars collided, but even then the explosions had to play out in a certain way. Nothing had been observed. At least until the 17th of August last year.
The LIGO gravity wave observatory caught the unmistakable signature of two neutron stars spiraling together and finally merging. At the same time a burst of gamma rays that alerted an orbiting patrol telescope that was sufficient cause to turn optical patrol telescopes to search a patch of sky about the area of a hundred and forty full moons for a fading point of light about 130 million light years away. A needle in the haystack, but the needle was fading. Eleven hours later, after discarding about two thousand candidates, it was found. Hundreds of astronomers dropped everything - the game was afoot. The observations took place from gamma ray to radio allowing astrophysicists to study the progression of the event across a good chunk of the electromagnetic spectrum. Combined with the gravity wave observations it is the first example of what is being called multi-messenger astronomy.
The event was not as spectacular as the first two gravity wave observations. They involved the merger of black holes each with masses twenty to thirty times that of the Sun. In the process they briefly shook the fabric of space-time with about the energy you'd get if you converted three Suns directly into energy - all in about a second. This new event, unpoetically labled GW170817, involved two neutron stars each with a mass about one and a half times larger than the Sun and roughly the diameter of Manhattan. The merger still converted a lot of mass into energy, but only about one fortieth the mass of the Sun this time. Big, but not stupendous. The violent merger sent a large cloud of matter traveling outward at nearly the speed of light. As it cooled some interesting physics took place and a pot of gold emerged.
Astrophysicists had already worked out what the signal for a kilonova and the existence of a process that made heavy metals (the r-process) would look like. At first the light was blue and decaying in a way consistent with the production of lighter heavy elements like silver. Four days out it reddened consistent with the production of the heavier gold, platinum and uranium. The amount of precious metals blasted out into space was, at least my my count, staggering. Somewhere between a few dozen and two hundred Earth masses of gold and five hundred of platinum. It is likely almost all of the gold found on Earth came about from neutron star mergers..
So while the event was not the most energetic ever, it was still impressive and more science has been learned from it than about anything in recently memory. It suggests this new type of astronomy that requires some of the most intense data analysis known will become very important.
And here's what the start of the process that lead to the creation of precious metals and some other heavy elements sounded like - a merger that took about a minute and shook space-time at a frequency in the human hearing range.
So for those who will win gold and silver .. that's where it came from.