Gold forged in nuclear furnace as stars collide
A gold mine on a cosmic scale has been found in a distant galaxy where astronomers watched the titanic collision between two super-dense neutron stars. John von Radowitz reports...
IN A kind of alchemy, a fireball 130 million light years away created huge quantities of gold, along with platinum, uranium and other heavy elements.
Scientists detected more gold than the whole of the Earth’s mass in the chemical signatures of the explosion, dubbed a “kilonova”.
Huge quantities of other precious metals, including platinum and uranium, were also forged in the nuclear furnace.
The discovery has been described as a “eureka moment” by Cardiff University scientists, who predicted it will lead to “a treasure trove of scientific results”.
A team from Cardiff were able to use the results to “measure the expansion of the universe more accurately than had ever been achieved before”.
The spectacular event was powerful enough to generate ripples in the very fabric of the universe, leading to the fifth detection of gravitational waves on Earth – a major discovery in itself.
Scientists not only “heard” the phenomenon by measuring vibrations in space-time, they also used satellite and ground-based telescopes to see the outburst of light and radiation.
Excited astronomers talked of opening a “new chapter in astrophysics” and unlocking a “treasure trove” of new science.
Professor Sheila Rowan, one of the many British scientists involved and director of the University of Glasgow’s Institute for Gravitational Research, said: “Nature has given us the most dazzling gift. The first gravitational wave signals from colliding neutron stars are a key that has allowed us to unlock the door to answer several long-standing mysteries. One of these... is the puzzle of where some of the gold and other heavy elements in the cosmos have come from. We now believe that the violent collision of neutron stars could be a gold factory.”
Based on the observations, scientists calculated that colliding neutron stars could account for half the gold and other heavy elements in the universe.
Every other gravitational wave detection has been traced to black holes crashing together in remote regions of the universe more than a billion light years away.
The new event – though still very distant – was much closer and completely different in nature. It was caused by colliding neutron stars – burned-out remnants of giant stars so dense that a teaspoon of their material on Earth would weigh a billion tons.
The two objects, each about 12 miles (19km) in diameter, stretched and distorted space-time as they spiralled towards each other and finally collided. Like ripples from a stone thrown in a pond, the gravitational waves fanned out across the universe at the speed of light.
They were picked up on Earth by two incredibly sensitive detectors in Washington and Louisiana in the US, operated by the Laser Interferometer Gravitational-Wave Observatory (Ligo).
It was here the first discovery of gravitational waves was made in September 2015, confirming a prediction made by Albert Einstein 100 years ago and earning three pioneers of the project a Nobel Prize.
Two seconds after the Ligo detection, a burst of gamma rays from the neutron star collision was captured by Nasa’s Fermi space telescope.
Astronomers around the world quickly turned their telescopes and dishes towards a small patch in the southern sky and also saw the flash across the visible and invisible light spectrum. Analysis of the light revealed something astonishing – the manufacture of gold and other heavy elements. The creation of heavy elements by colliding neutron stars had previously been theorised but not observed.
Dr Joe Lyman, from the University of Warwick, said: “Heavy elements, like the gold or platinum in jewellery, are the cinders, forged in the billion-degree remnants of a merging neutron star.”
A third gravitational wave facility called Virgo, near Pisa in Italy, also registered a faint signal from the event, allowing scientists to triangulate its position.
The neutron star collision took place 130 million light years away in a relatively old galaxy called NGC 4993. When the gravitational waves began their journey across space, dinosaurs roamed the Earth. The gravitational wave signal, named GW170817, was detected at 1.41pm UK time on August 17.
A tight lid was kept on the findings until the publication of a series of papers in journals including Nature, Nature Astronomy, Science, Physical Review Letters, and the Astrophysical Journal.
The international researchers expect to spend many months trawling through the mountain of data.
One question already answered is the origin of short-duration gamma ray bursts. Gamma ray bursts (GRBs), marked by an eruption of gamma rays lasting milliseconds to several minutes, are the most powerful explosions known.
Scientists now know that one type of GRB is generated when neutron stars collide.
In addition, astronomers were able to use the gravitational wave detections to measure the expansion of the universe more accurately than had ever been achieved before.
British Ligo scientist Professor BS Sathyaprakash, from Cardiff University, described the new discovery as “truly a eureka moment”.
He added: “The 12 hours that followed are inarguably the most exciting hours of my scientific life. This event marks a turning-point in observational astronomy and will lead to a treasure trove of scientific results.”
Professor Bernard Schutz, also from Cardiff University, told how his team used the gravitational wave detections to measure the expansion of the universe more accurately than had ever been achieved before.
“What has amazed me... is that with just this one measurement, we got a result right in the middle between the two rather different values that astronomers have measured recently,” he said.
Professor Bob Nichol, director of the Institute of Cosmology and Gravitation at the University of Portsmouth, said: “It doesn’t get more exciting than this for an astronomer.”
US scientist Dr David Shoemaker, from the Massachusetts Institute of Technology, spokesman for the Ligo scientific collaboration, said: “This event is just so rich. It is a gift that will keep on giving.”
Ligo colleague Professor Laura Cadonati, from the Georgia Institute of Technology in the US, said: “This detection has genuinely opened the doors to a new way of doing astrophysics.”