美国国家公共电台 NPR A 4 Billion Light-Year Journey Ends At The South Pole（在线收听）

MARY LOUISE KELLY, HOST:

Scientists announced today that for the first time, they have been able to pinpoint the source of a particle called a high-energy neutrino. It was detected by an observatory at the South Pole. And as NPR science correspondent Joe Palca reports, finding the source of this particle opens a whole new way of looking at the universe.

JOE PALCA, BYLINE: At the South Pole, there's a sophisticated observatory designed to catch high-energy neutrinos, enigmatic particles produced by violent cosmic events like exploding stars. Neutrinos are sometimes called the ghost particle because they can travel virtually unimpeded across the universe. When a particularly powerful neutrino is captured, IceCube sends out an alert.

OLGA BOTNER: We had this neutrino alert in September 2017.

PALCA: Olga Botner is a particle physicist at Uppsala University in Sweden. I reached her via Skype. When the alert went out, a bevy of observatories on Earth and in space started searching the portion of the sky where the neutrino appeared to be coming from, looking for something that might have generated it. There had been other alerts, but each time, the search turned up empty. This time, as they report in the journal Science, telescopes saw a burst of energy coming from an object 4 billion light years from Earth called a blazar.

BOTNER: Blazars are very special objects. They are intensely bright galaxies harboring a black hole at the center.

PALCA: Botner says the black holes are spinning, and jets of energetic particles shoot out from the top and bottom, traveling at close to the speed of light.

BOTNER: And the nice thing about blazars is that one of these jets is pointing directly towards Earth.

PALCA: So 4 billion years ago, a jet from this blazar sent a neutrino zooming toward Earth, and that neutrino was captured at the South Pole last September.

KE FANG: Those jets are a very interesting subject for astrophysicists...

PALCA: Ke Fang is an astrophysicist at the University of Maryland.

FANG: ...Because these are direct outputs from those black holes.

PALCA: Fang says the hope is more of these neutrinos will be detected, and that should give physicists more information about the physics that govern how black holes behave. In fact, now that they know it's possible, studying neutrinos given off by celestial objects opens a whole new way of looking at the universe.

NAOKO KURAHASHI NEILSON: Astronomy started when people looked at the night sky, and that's light hitting your eyes.

PALCA: Naoko Kurahashi Neilson is an astrophysicist at Drexel University in Philadelphia.

NEILSON: It's expanded from just visible light to X-rays and gamma rays and also to infrared and radio waves.

PALCA: But light waves and gamma rays and even radio waves are all what scientists call electromagnetic radiation. They differ in wavelength, but they're all from the same family.

NEILSON: And then here comes neutrinos, which is a completely different way to look at the universe. And, gee, I wonder what we can see if we use this whole different way to look at the universe.

PALCA: Of course scientists don't know what they'll find, but then that's the whole point, isn't it? Joe Palca, NPR News.