The Associated Press
Seth Borenstein
WASHINGTON–It was a faint signal but it told of one of the most violent acts in the universe.
And it soon would reveal secrets of the cosmos, including how gold was created.
Astronomers around the world reacted to the signal quickly, focusing telescopes located on every continent–and even in orbit–to a distant spot in the sky.
What they witnessed in mid-August and revealed yesterday was the long-ago collision of two neutron stars–a phenomenon California Institute of Technology’s David H. Reitze called “the most spectacular fireworks in the universe.”
“When these things collide, all hell breaks loose,” he said.
Measurements of the light and other energy emanating from the crash have helped scientists explain how planet-killing gamma ray bursts are born, how fast the universe is expanding, and where heavy elements like platinum and gold come from.
“This is getting everything you wish for,” said Syracuse University physics professor Duncan Brown, one of more than 4,000 scientists involved in the blitz of science that the crash kicked off.
“This is our fantasy observation.”
It started in a galaxy called NGC 4993, seen from Earth in the Hydra constellation.
Two neutron stars (collapsed cores of stars so dense that a teaspoon of their matter would weigh one billion tons) danced ever faster and closer together until they collided, said Carnegie Institution astronomer Maria Drout.
The crash (called a kilonova) generated a fierce burst of gamma rays and a gravitational wave–a faint ripple in the fabric of space and time first theorized by Albert Einstein.
“This is like a cosmic atom smasher at a scale far beyond humans would be capable of building,” said Andy Howell, a staff scientist at the Las Cumbres Observatory.
“We finally now know what happens when an unstoppable force meets an immovable object, and it’s a kilonova.”
The crash happened 130 million years ago, while dinosaurs still roamed on Earth, but the signal didn’t arrive on Earth until Aug. 17 after travelling 130 million light-years.
A light-year is 5.88 trillion miles.
Signals were picked up within 1.7 seconds of each other by NASA’s Fermi telescope, which detects gamma rays, and gravity wave detectors in Louisiana and Washington state that are a part of the LIGO Laboratory (whose founders won a Nobel Prize earlier this month).
A worldwide alert went out to focus telescopes on what became the most well-observed astronomical event in history.
Before August, the only other gravity waves detected by LIGO were generated by colliding black holes.
But black holes let no light escape so astronomers could see nothing.
This time, there was plenty to see, measure, and analyze: matter, light, and other radiation.
The Hubble Space Telescope even got a snapshot of the afterglow.
Finding where the crash happened wasn’t easy. Eventually scientists narrowed the location down to 100 galaxies, began a closer search of those, and found it in the ninth galaxy they looked at.
It is like “the classic challenge of finding a needle in the haystack, with the added challenge that the needle is fading away and the haystack is moving,” said Marcelle Soares-Santos, an astrophysicist at Brandeis University.
“The completeness of this picture from the beginning to the end is unprecedented,” noted Columbia University physics professor Szabolcs Marka.
“There are many, many extraordinary discoveries within the discovery.”
The colliding stars spewed bright blue, super-hot debris that was dense and unstable.
Some of it coalesced into heavy elements, like gold, platinum, and uranium.
Scientists had suspected neutron star collisions had enough power to create heavier elements, but weren’t certain until they witnessed it.
“We see the gold being formed,” said Syracuse’s Brown.
Calculations from a telescope measuring ultraviolet light showed the combined mass of the heavy elements from this explosion is 1,300 times the mass of Earth.
And all that stuff–including lighter elements–was thrown out in all different directions and now is speeding across the universe.
Perhaps one day the material will clump together into planets the way ours was formed, Reitze said–maybe ones with rich veins of precious metals.
“We already knew that iron came from a stellar explosion, the calcium in your bones came from stars, and now we know the gold in your wedding ring came from merging neutron stars,” said University of California Santa Cruz’s Ryan Foley.
