LIGO Detects Fierce Collision of Neutron Stars for the First Time - Physics-Astronomy.org

LIGO Detects Fierce Collision of Neutron Stars for the First Time

This is the story of a gold rush in the sky.
Astronomers have now seen and heard a pair of dead stars collide, giving them the first glimpse of what they call a “cosmic forge,” where the world’s jewels were minted billions of years ago.
The collision rattled space-time and sent a wave of fireworks across the universe, setting off sensors in space and on Earth on Aug. 17 as well as producing a long loud chirp in antennas designed to study the Einsteinian ripples in the cosmic fabric known as gravitational waves. It set off a stampede around the world as astronomers scrambled to turn their telescopes in search of a mysterious and long-sought kind of explosion called a kilonova.

After two months of underground and social media rumblings, the first wave of news is being reported Monday about one of the least studied of cosmic phenomena: the merger of dense remnants known as neutron stars, the shrunken cores of stars that have collapsed and burst.
Such collisions are thought to have profoundly influenced the chemistry of the universe, creating many of the heavier elements in the universe, including almost all the precious metals like gold, silver, platinum and uranium. Which is to say that the atoms in your wedding band, in the pharaoh’s jewels and the bombs that destroyed Hiroshima and still threaten us all were formed in a cosmic gong show that reverberated across the heavens billions of years ago.As astronomers gather for news conferences in several cities around the world, a blizzard of papers are being published, including one in The Astrophysical JournalLetters that has 4,500 authors — a third of all the professional astronomers in the world — from 910 institutions. “That paper almost killed the paperwriting team,” said Vicky Kalogera, a Northwestern University astrophysicist who was one of 10 people who did the actual writing.More papers are appearing in Nature and in Science, on topics including nuclear physics and cosmology.
“It’s the greatest fireworks show in the universe,” said David Reitze of the California Institute of Technology and the executive director of the Laser Interferometer Gravitational-Wave Observatory, or LIGO.
Daniel Holz, an astrophysicist at the University of Chicago and a member of the LIGO Scientific Collaboration, a larger group that studies gravitational waves, said, “I can’t think of a similar situation in the field of science in my lifetime, where a single event provides so many staggering insights about our universe.”
It was a century ago that Albert Einstein predicted that space and time could shake like a bowl of jelly when massive things like black holes moved around. But such waves were finally confirmed only in 2016, when LIGO recorded the sound of two giant black holes colliding, causing a sensation that eventually led this month to a Nobel Prize.

For the LIGO researchers, this is in some ways an even bigger bonanza than the original discovery. This is the first time they have discovered anything that regular astronomers could see and study. All of LIGO’s previous discoveries have involved colliding black holes, which are composed of empty tortured space-time — there is nothing for the eye or the telescope to see.But neutron stars are full of stuff, matter packed at the density of Mount Everest in a teaspoon. When neutron stars slam together, all kinds of things burst out: gamma rays, X-rays, radio waves. Something for everyone who has a window on the sky.
“Joy for all,” said David Shoemaker, a physicist at the Massachusetts Institute of Technology who is the spokesman for the LIGO Scientific Collaboration.It began on the morning of Aug. 17, Eastern time. Dr. Shoemaker was on a Skype call when alarms went off. One of the LIGO antennas, in Hanford, Wash., had recorded an auspicious signal and sent out an automatic alert. Twin antennas, in Washington and Louisiana, monitor the distance between a pair of mirrors to detect the submicroscopic stretching and squeezing of space caused by a passing gravitational wave. Transformed into sound, the Hanford signal was a long 100-second chirp, that ended in a sudden whoop to 1000 cycles per second, two octaves above middle C. Such a high frequency indicated that whatever was zooming around was lighter than a black hole.
Checking the data from Livingston to find out why it had not also phoned in an alert, Dr. Shoemaker and his colleagues found a big glitch partly obscuring the same chirp.
Meanwhile, the Fermi Gamma-Ray Space Telescope, which orbits Earth looking at the highest-energy radiation in the universe, recorded a brief flash of gamma rays just two seconds after the LIGO chirp. Fermi sent out its own alert. The gamma-ray burst lasted about two seconds, which put it in a category of short gamma ray bursts associated with the formation of black holes perhaps as a result of neutron stars colliding.

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