In a highly anticipated first, scientists said they've detected the collision of two neutron stars and confirmed that these cataclysmic events are indeed a source of gold, platinum and other heavy elements in the universe.
The powerful smash-up produced gravitational waves that were picked up by the LIGO and Virgo observatories. It also emitted a broad swath of electromagnetic radiation that could be seen by more traditional telescopes, including ones that capture visible light.
By studying the gravitational waves, gamma rays, X-rays, ultraviolet light, infrared, radio waves and visible light from a single event, the scientists said they have embarked on the era of multi-messenger astronomy _ one that promises a far deeper understanding of some of the most powerful and elusive phenomena in the cosmos.
"This is the beginning," said Duncan Brown, a gravitational-wave astronomer at Syracuse University and member of the LIGO Scientific Collaboration. "This is the beginning of bringing the entire human toolkit of observations, of gravitational waves and electromagnetic waves, to bear on understanding our universe and where we live."
The findings, described in a suite of papers released Monday, mark the first time the larger astronomical community has been able to study a gravitational-wave event.
Previously, LIGO and its European partner Virgo have picked up only collisions between black holes _ powerful events that can't be detected with telescopes because not even light can escape a black hole's powerful gravitational pull.
But scientists with the LIGO-Virgo collaboration have been itching to find a collision between two neutron stars because it would produce both gravitational waves and electromagnetic waves.
Neutron stars are the corpses of massive stars that have burned out in supernova explosions. While they're not that big, they're incredibly dense, packing a sun's worth of mass into the size of a city. A teaspoon of neutron-star stuff weighs around a billion or so tons.
The cosmic crash described Monday occurred about 130 million light-years away in the constellation Hydra, said David Reitze, executive director of the LIGO Laboratory at Caltech. After a long dance toward each other, two neutron stars _ one somewhere around 1.1 solar masses, the other weighing in the neighborhood of 1.6 suns _ finally collided, converting some of their combined mass into gravitational waves.
These waves are ripples created by objects as they accelerate or decelerate, rather like the wake made by a boat moving through the water. Albert Einstein predicted their existence 101 years ago as part of his general theory of relativity, and LIGO scientists won a Nobel Prize this month for detecting gravitational waves and proving Einstein correct.
Earth's first inkling of the neutron-star collision came on Aug. 17, after LIGO's twin detectors in Hanford, Wash., and Livingston, La., measured a powerful gravitational "chirp."
This signal, dubbed GW170817, looked very different from the waves produced by colliding black holes, Reitze said. Since neutron stars are less massive than black holes, a doomed pair takes longer to complete its final death spiral and packs many more waves into a single event.
Around that time, NASA's Fermi Gamma-ray Space Telescope picked up a powerful flash of high-energy gamma rays. (The gamma rays are produced after the gravitational waves, but Fermi was the first to send out an alert.)
Both Fermi as well as the LIGO and Virgo detectors were able to identify a patch of sky that was the likely source of their event _ and those two areas overlapped.
Within hours, astronomers were training their telescopes on that promising region, looking for X-rays, ultraviolet waves, optical light, infrared light and radio waves. Each of these bands of the electromagnetic spectrum yields different kinds of information about the source, allowing the researchers to study this neutron-star collision in unprecedented detail.
Among their discoveries: Infrared cameras found signs that heavy elements such as gold, platinum and neodymium had been produced by this powerful event. While nickel, copper, iron and other elements can be produced by supernovae, scientists have long suspected that many elements heavier than iron are born from of the collision between neutron stars.
"They're really cosmic foundries for heavy elements like gold, platinum, uranium," Reitze said. "That's pretty amazing."
The findings could explain the mysterious origins of a type of gamma-ray burst known as "short-hard," which produces brief but highly energetic gamma-ray bursts _ powerful flashes of light.
"That just solved a long-standing problem in astrophysics," Brown said.
