美国国家公共电台 NPR Astronomers Strike Gravitational Gold In Colliding Neutron Stars（在线收听）

MARY LOUISE KELLY, HOST:

For the first time, scientists have seen the violent collision of two neutron stars. They've watched as heavy elements like gold, platinum and uranium were forged. This cosmic smashup is being hailed as one of the biggest events ever in astrophysics. NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: On the morning of August 17, David Shoemaker was sitting in a boring meeting when he got an alert.

DAVID SHOEMAKER: A phone alarm went off in my pocket that said something interesting has happened.

GREENFIELDBOYCE: David Shoemaker is a physicist at MIT who studies gravitational waves. Those are ripples in the fabric of space-time that are created when something big in the universe goes boom. His phone had buzzed because some of those waves had been picked up by two giant detectors. What's more, just as the waves arrived, an orbiting NASA satellite saw a pulse of high-energy light.

SHOEMAKER: And that put us into a very high state of excitement.

GREENFIELDBOYCE: The detectors Shoemaker works on are called LIGO. In the past, LIGO has picked up waves created by two black holes colliding. But that kind of crash doesn't generate any light, so this was something new. The LIGO researchers sent out a bulletin to astronomers all over the world telling them where to point their telescopes. Benjamin Shappee with the University of Hawaii was in Chile. He and his colleagues had to wait for sunset. But once it got dark, the team almost immediately found it - a new spot of light in the sky.

BENJAMIN SHAPPEE: It just felt - to me at the time, I was like, this is almost too easy. It was, like, almost too perfect.

GREENFIELDBOYCE: The little circle of light started out bright and blue. Over the next few days, it faded and became redder as scientists around the world watched with awe. What they were seeing was the fiery collision of two neutron stars 130 million light-years away. Neutron stars are stars but weird ones.

EDO BERGER: Each one is about the size of a city like Boston or New York or Seattle but weighing more than the mass of the sun.

GREENFIELDBOYCE: Edo Berger is an astrophysicist at Harvard. He says when two circling neutron stars finally collide, they're going fast - about a third of the speed of light.

BERGER: So it's this amazing, powerful head-on collision between these two extremely dense objects, I think one of the most extreme events one could imagine in space.

GREENFIELDBOYCE: And it used to be that imagining was all anyone could do. Daniel Kasen is a theoretical astrophysicist at the University of California, Berkeley. He spent years thinking about colliding neutron stars, so watching this unfold was uncanny.

DANIEL KASEN: Even though this was an event that had never been seen before in human history, what it looked like was, you know, deeply familiar because it resembled very closely to the predictions that we had been making.

GREENFIELDBOYCE: And seeing this solved a longstanding mystery in astrophysics. Where do heavy elements like gold and platinum come from? Kasen says this neutron star collision created a cloud of radioactive waste the size of our solar system filled with an astonishing haul of precious metal.

KASEN: We estimate that there's maybe, you know, upwards of 200 Earth masses of pure gold in this cloud and probably even more platinum - maybe 500 Earth masses worth. Today, major science journals published a bunch of reports on all these observations authored by more than 3,000 researchers. One of them is Peter Saulson of Syracuse University.

PETER SAULSON: It's so beautiful. It's so beautiful. It makes me want to cry.

GREENFIELDBOYCE: He says this is not just the fulfillment of thousands of people's efforts.

SAULSON: But it's also the fulfillment of, you know, an idea suddenly becoming real.

GREENFIELDBOYCE: It was Albert Einstein over a century ago who predicted that gravitational waves should exist. The work that led to the first detections won the Nobel Prize earlier this month. And as this latest discovery shows, scientists now have a powerful new way to see the most extreme events in the universe. Nell Greenfieldboyce, NPR News.

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