Proof that celestial collisions called kilonovas create gold is the first wonder to arise from coordinated observations – expect more to come

If you are wearing a piece of gold jewellery, take a good, hard look at it and consider this: you are likely to be wearing the celestial debris of a cataclysmic stellar collision, a collision so devastating that it literally shook the universe. That’s the conclusion from Monday’s announcement of gravitational wave signal GW170817.

It is another reminder that we are intimately connected to the cosmos around us. At heart, astronomy is not really about remote and abstracted realms, instead it informs us about our own origins and the origins of those things we value.

New frontier for science as astronomers witness neutron stars colliding Read more

Astronomically, the origin of gold has been a puzzle for decades. The recognition that stars shine because they fuse one chemical element into another was made in the 1920s. It suggested that stars are the chemical factories that build almost everything in the chemist’s periodic table, but the details were elusive.

Astronomers have since established that the simplest elements – hydrogen and helium – were made during the origin of the universe in the fireball of the big bang. The rest of the naturally occurring elements come in various quantities from dying, exploding or colliding stars.

Play Video 1:35 Why discovering gravitational waves was a big deal – video

Monday’s announcement confirms research from 2013 that shows that a significant fraction of the gold and other heavy elements could come from the collision of two super-dense celestial objects known as neutron stars. The resulting explosion is known as a kilonova.

The hunt is on for gravity waves Read more

A neutron star is the burned-out core of a once-giant star that exploded long ago. This particular pair was initially separated by 200 miles, but spiralled towards each other so rapidly that they met 100 seconds later. Situated about 130m light years from Earth, each neutron star was around 12 miles (19km) in diameter and contained a mass about half a million times that of the Earth.

The final moments of their spiral and the actual collision itself generated the gravitational waves. These were detected at 1:41pm UK time on 17 August by two identical detectors in the US (Washington state and Louisiana), and a third detector in Pisa, Italy. It triggered a worldwide alert for other astronomers to try to find the event with traditional telescopes.

Facebook Twitter Pinterest Sky localisations of gravitational-wave signals detected by Ligo beginning in 2015 (GW150914, LVT151012, GW151226, GW170104), and, more recently, by the LIGO-Virgo network (GW170814, GW170817). Photograph: LIGO/Virgo/Nasa/Leo Singer (Milky Way image: Axel Mellinger)

At the time of the first gravitational wave detection in February 2016 there was talk about how this was the equivalent of a new sense for astronomers. Being ripples in the fabric of space, gravitational waves were said to be rather like the cosmological equivalent of sound. It would be like going from silent movies to talkies. This is now coming true because at almost the same time that the gravitational waves were discovered, Nasa’s Fermi observatory registered a short burst of gamma rays.

Such short gamma ray bursts have been known about for years. Analysis suggested that they were the result of a collision between two neutron stars but clinching evidence has always eluded astronomers. Until now.

The gravitational wave signal shows clearly that they were neutron stars not their larger cousins, black holes. Follow-up observations taken with ground-based telescopes captured the flash of the explosion and showed astronomers the chemical fingerprint of the atoms in the debris, including significant quantities of gold.

Facebook Twitter Pinterest The left panel is a visualisation of the matter of the neutron stars, the right panel shows how space-time is distorted near the collisions.

This mixture of gravitational waves and traditional observations is the opening of the astronomical flood gates. Such coordinated observations are going to become the norm for astronomers. And as they do, expect more wonders and more links to be found between us and the wider cosmos.

Stuart Clark is the author of The Unknown Universe (Head of Zeus).