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Two stars crash into each other, wobbling the universe and flinging out huge amounts of gold

The discovery opens a 'new chapter in astrophysics', say experts, and has been described as one of the most exciting ever

The Guardian | 16 October 2017

Two stars slammed into each other deep in space, sending out huge amounts of gold in an alchemical explosion.

The super-dense stars crashed 130 million light years away, spewing out precious metals and other heavy elements like platinum and uranium, scientists say. And now the explosion has kickstarted a "new chapter in astrophysics", and confirmed theories about the origin of the mysterious neutron stars.

The huge explosion rocked the fabric of the universe, distorting spacetime. That is a major discovery in itself, marking only the fifth time that gravitational waves have been spotted on Earth.

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Scientists not only "heard" the phenomenon by measuring vibrations in space-time, they also used satellite and ground-based telescopes to see light and radiation pouring out of the stellar fireball, dubbed a "kilonova".

Excited astronomers talked of opening a "new chapter in astrophysics" and unlocking a "treasure trove" of new science.

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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 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 on a cosmic scale, as well as other heavy elements.

Dr Joe Lyman from the University of Warwick, one of many British scientists involved, said: "The exquisite observations obtained in a few days showed we were observing a kilonova, an object whose light is powered by extreme nuclear reactions.

"This tells us that the heavy elements, like the gold or platinum in jewellery, are the cinders, forged in the billion degree remnants of a merging neutron star."

The origins of gold and other heavy elements have been a long-standing mystery, but recent evidence has suggested that colliding neutron stars could have a hand in their creation.

A third gravitational wave facility called Virgo near Pisa, 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.

Ligo's detectors, consisting of L-shaped tunnels with arms 2.5 miles (4km) long, use laser beams bouncing off mirrors to measure movement across a distance 10,000 times smaller than the width of a proton, the kernel of an atom.

A tight lid was kept on the findings until the publication of a series of papers in journals including Nature, Nature Astronomy, and Physical Review Letters.

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.

Dr Samantha Oates, also from the University of Warwick, said: "This discovery has answered three questions that astronomers have been puzzling for decades: what happens when neutron stars merge? What causes the short duration gamma-ray bursts? Where are the heavy elements, like gold, made?

"In the space of about a week all three of these mysteries were solved."

Colleague Dr Danny Steeghs said: "This is a new chapter in astrophysics."

British Ligo scientist Professor BS Sathyaprakash, from the University of Cardiff, 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 the University of Cardiff, 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.

Dr David Shoemaker, spokesman for the Ligo scientific collaboration and senior research scientist at the US Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research, said: "From informing detailed models of the inner workings of neutron stars and the emissions they produce, to more fundamental physics such as general relativity, this event is just so rich.

"It is a gift that will keep on giving."

Ligo colleague Professor Laura Cadonati, from Georgia Institute of Technology, US, said: "This detection has genuinely opened the doors to a new way of doing astrophysics.

"I expect it will be remembered as one of the most studied astrophysical events in history."