Where gold comes from

Explosive: The event happened when dinosaurs roamed Earth, but its effects reached us in August.

Astronomers have witnessed an explosion 1,000 times brighter than a supernova, which sent gold and platinum cascading into the universe, and caused ripples in space and time itself...

  • So — where does gold come from?

    It comes from the stars. To be more specific, it comes from the collision of two neutron stars, which are the dead husks left behind after supernovae. When two of these get caught in each other’s orbits, they get closer and closer until eventually they crash into each other. This was observed for the very first time in August this year, and astronomers announced the results on Monday.

    Neutron stars are small compared to most other important objects in space (the two recorded in August were about the size of London) but they are very heavy. A single teaspoon full would weigh about the same as Mount Everest. So when they slam into each other, the explosion is hot enough to fuse 79 protons with 118 neutrons, and make a particle of gold. Or, in this case, 236 sextillion tonnes of gold — and also platinum, silver, and other heavy elements which were then spewed into space.

  • That sounds intense.

    It was. Scientists have known about the elements of the periodic table for a long time. But until now, they were unsure what was powerful enough to make the heavy metals that we earthlings are fond of turning into jewellery.

    Now they know that, sometimes at least, they come from such an explosion — also known as a kilonova.

  • Great name. How was this kilonova detected?

    Buckle up: finding out where gold comes from is just one part of a much bigger story.

    In 2015, astronomers detected gravitational waves for the first time. These are tiny ripples in space and time, caused by violent events like the one recorded in August. But over the last two years, scientists have only been able to record the waves coming from two black holes colliding.

    We cannot see black holes, because by their nature they suck light in rather than emit it. But we can see neutron stars. So when scientists detected the gravitational waves in August, within seconds powerful telescopes all over the world had swivelled around to take a look. “It was the astronomical equivalent of stopping traffic," explained one scientist.

  • Why is it such a big deal?

    It was a massive deal when physicists first detected gravitational waves in 2015; they were finally able to prove Einstein’s theories 100 years after he made them. Earlier this year, three physicists won the Nobel prize for it. But this time, astronomers were able to combine the gravitational waves with the observations made through telescopes. They could see what happened for the first time.

    One scientist said this was like going from “looking at a black-and-white picture… to sitting in an IMAX 3D movie”.

    Another called it a “new era” in astrophysics. Another compared the findings to the Rosetta stone. The simple fact is that they have far more data to work with than they did before.

  • What else did they discover?

    The kilonova confirmed a lot of things which scientists already suspected — such as that gravitational waves do indeed travel at the same speed as light, and that short bursts of gamma rays can also come from two neutron stars. Then they were able to use the kilonova to measure the rate at which the universe is expanding; happily, it fits with their current estimations.

  • What might they learn next?

    What is left in the place of the two neutron stars: the current candidates are a single, much heavier neutron star or a light black hole.

    After that, who knows? But scientists predict that they will keep getting better at recording gravitational waves. “It’s rather like being an explorer setting foot on a new shore and there’s a whole continent ahead of us,” said one. “I for one cannot wait to get exploring.”

You Decide

  1. Does knowing where gold comes from change how you think of it?

Activities

  1. Create a timeline which shows the most important events in the history of astronomy. Will you include this one?

Subjects

Word Watch

Protons
A subatomic particle with a positive electric charge, found in the nucleus of an atom. The number of protons in an atom determines what kind of element it is.
Neutrons
A subatomic particle with no electric charge, found in the nucleus of an atom.
Heavy elements
Fusing atoms together to make a new element requires enormous amounts of energy. Scientists had been unsure what was powerful enough to create anything heavier than iron, which has 26 protons. But they knew that something must be, because heavier atoms exist. Now they have an answer.
Gravitational waves
These were detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO).
Einstein’s theories
Gravitational waves prove Einstein’s theory of general relativity: that time and space are the same thing, and that heavy objects like planets and stars distort it. This distortion is what creates gravity.
Rosetta stone
An ancient stone, containing three translations of the same thing, which helped historians to decipher Egyptian hieroglyphs.
Gamma rays
The most powerful form of electromagnetic radiation.

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Where gold comes from
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