‘Gold is forged in the nuclear furnace of neutron star collisions.’

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  1. Wonderful read.
    A Clash of Neutron Stars Forges Gold
    Researchers say this is the first time a cosmic event has been seen both with gravitational waves and with the full electromagnetic spectrum
    Artist's concept of the explosive collision of two neutron stars.PHOTO: ILLUSTRATION BY ROBIN DIENEL/CARNEGIE INSTITUTION FOR SCIENCE


    Robert Lee Hotz

    Oct. 16, 2017 10:00 a.m. ET
    Astronomers scanning ripples in space-time have detected the collision of two neutron stars for the first time—and, by analyzing the flare from the cataclysmic crush, discovered such stellar smashups are the source of gold, platinum, uranium and other heavy elements found throughout the universe.

    The discovery, documented in a series of new research papers, was announced Monday at a news conference in Washington, D.C. The findings were the work of thousands of researchers at three sprawling gravitational wave detectors in the U.S. and Italy, which first picked up signals from the merging stars, and astronomers at more than 70 observatories around the world who scrambled to study its exotic effects before the fierce afterglow faded.

    “Gold is forged in the nuclear furnace of neutron star collisions,” said astrophysicist Duncan Brown, who studies gravitational waves at Syracuse University and who was involved in the effort. “In the strictest sense of turning matter into gold, this is where alchemy happens.”

    The researchers said it marks the first time any cosmic event has been seen both with gravitational waves, which are produced when massive objects such as black holes stretch and squeeze the fabric of space and time, and with the full electromagnetic spectrum, from gamma rays, X-rays and radio waves to infrared, ultraviolet and visible light.

    “This is a new kind of astronomy,” said physicist David Reitze at the California Institute of Technology, who is executive director of the $1.1 billion U.S.-based Laser Interferometer Gravitational-wave Observatory, or LIGO, which caught the first signal from the merging stars. While optical astronomy is almost as old as humankind, gravitational waves were detected for the first time in 2015. Earlier this month, three scientists who conceived and managed the LIGO detector received the Nobel Prize in Physics for their work.

    Created in the collapse of a supernova, neutron stars are the smallest densest stars in the known cosmos—so tiny that the two scrutinized in the new studies were each about the size of Manhattan, so heavy that each contained more than the mass of the sun, and so compacted that a spoonful of their exotic essence likely would weigh more than a billion tons, the researchers said.

    Normally, neutrons stars are too faint to be detected from Earth. But as these two spiraled together—barely 200 miles apart and traveling at about one-third the speed of light—they triggered gravitational shock waves that rippled across the sea of space and time, said gravitational wave researcher David Shoemaker at the Massachusetts Institute of Technology, who is the spokesman for the LIGO Scientific Collaboration.

    “When these two neutron stars collide, all hell breaks loose,” Dr. Reitze said.

    Among astrophysicists, astral engineers and astronomers, it touched off a frenzy of discovery.

    ‘Gold is forged in the nuclear furnace of neutron star collisions.’

    —Duncan Brown, astrophysicist at Syracuse University
    The detector alarm first rang at the LIGO installation in Hanford, Wash., at 8:41 a.m. EDT Aug. 17. Almost immediately, the researchers confirmed the signal at LIGO’s second installation 1,800 miles away at Livingston, La., which operates in tandem with the Hanford center to cross-check results.

    Less than two seconds after the first gravitational waves from the merging neutron stars reached Earth, NASA’s orbiting Fermi Gamma Ray Observatory picked up a burst of high-energy light like a flash bulb in the southern sky. Called a gamma ray burst, these flashes typically are the brightest and most energetic phenomena in the known universe, second only to the Big Bang itself.

    Longer bursts form when a huge star collapses into a black hole. Until now, the source of short bursts had been a mystery.

    An image of Swope Supernova Survey 2017a from the night of discovery. On Aug. 17, a team of four astronomers provided the first-ever glimpse of two neutron stars colliding, opening the door to a new era of astronomy.PHOTO: TONY PIRO/UC SANTA CRUZ/CARNEGIE OBSERVATORIES

    Persuaded that they were witnessing the same neutron star collision, the LIGO astrophysicists and Fermi astronomers still weren’t sure where exactly the merging stars were located. Scientists at the newly opened Virgo gravitational wave detector in Pisa, Italy, operated by the European Gravitational Wave Observatory, helped narrow the search for the source of the signal to a region of the Southern Hemisphere sky.

    The patch of sky they targeted, however, likely contained as many as 50 galaxies. They alerted astronomers around the world.

    Within hours, seven astronomers at the Swope Telescope in Chile—a vintage optical telescope at the Carnegie Observatories’ Las Campanas Observatory—picked out a bright new blue orb glowing in normal visible light in the zone singled out by the gravitational wave and gamma ray signals. It was located in a distant galaxy cataloged as NGC 4993, about 130 million light years from Earth.

    In their collision, the two neutron stars ejected debris equal to the mass of about 10,000 planets the size of Earth, the researchers calculated.

    As the astronomers using the Hubble Space Telescope and other observatories watched this radioactive plume of neutrons decay into other substances, they saw evidence of the creation of so-called “r-process” elements, which account for about half of all the heavy elements in the universe.

    “The neutrons can condense down into the heavy elements—gold, platinum and others—that make pretty jewelry so pretty,” Dr. Shoemaker said.

    No one is sure how these enriched plumes from the wreckage of neutron stars might seed worlds like Earth with veins of precious metals. Astronomers speculate that perhaps a plume could condense into a rain of meteors rich with heavy elements or develop into a swirling disk of dust from which new stars and planets are thought to form.

    Write to Robert Lee Hotz at sciencejournal@wsj.com