国家地理-2008-05-03 Planetary Life After Death 浴火重生的行星（在线收听）

Like a phoenix rising from the ashes, astronomers have found a whole new solar system may be forming in the wake of a star's violent death.

This is the Hidden Universe of the Spitzer Space Telescope, exploring the mysteries of infrared astronomy with your host Dr. Robert Hurt.

When a massive star reaches the end of the line, it ''does not go gentle into that good night''. It becomes a supernova, an explosion so bright that it briefly outshines everything else in the galaxy. Most of the heavy elements that make up planets, and even people, are forged in the nuclear furnaces of such explosions. Here we see heavy elements in the Cassiopeia A supernova remnant blowing back into the galaxy and mingling with interstellar gases. The next generation of baby stars forms from this material now enriched with building blocks for growing new solar systems and planets.

But what of the star that went supernova? Its core still remains in the form of a pulsar. This stellar corpse is tiny and dense, squeezing about 1.5 times the mass of the Sun into an object a mere 10 miles across.

A team led by Dr. Deepto Chakrabarty at the Massachusetts Institute of Technology has found that even a dead pulsar might play host to a whole new generation of planet formation. They studied a once-massive star that went supernova about 100,000 years ago. In the process it likely wiped out any existing planets. While most of the star-stuff blew off into space, a little bit fell back under the pull of gravity. Dr. Chakrabarty explains. "If the original massive star was spinning fast enough then that material won't fall directly back onto the neutron star, but may instead form a disk, and so what we think we've found is a disk of this debris material that's left over from the explosion that formed the neutron star.

This disk has about 10 times the Earth's mass and looks very much like ones that produce planets around young stars. Moreover, it may help solve a recent planet-making mystery. In 1992, astronomers found the first planets outside our solar system, which were orbiting an older pulsar. But where did they come from? Could they have formed after their star went supernova? The discovery of a planet forming disk around a younger pulsar makes this likely. It seems new planets can arise from the ashes of their own star's death.

However pulsar planets are pretty hostile real estate for life. Pulsars provide little light or heat and would bathe these worlds in intense radiation. A nuclear waste dump at the South Pole might actually be a little more pleasant.

1. end of the road/line
n. phr. The final result or end (as of a way of action or behavior); the condition that comes when you can do no more.

2. Do Not Go Gentle Into That Good Night
a villanelle composed in 1951, is considered to be among the finest works by Welsh poet Dylan Thomas (1914–1953). Originally published in the journal Botteghe Oscure in 1951, it also appeared as part of the collection "In Country Sleep." It is one of his most-quoted works. It was written for his dying father.

3. supernova 超新星
a very large exploding star

4. Cassiopeia 仙后座
A W-shaped constellation in the Northern Hemisphere between Andromeda and Cepheus.

5. remnant
a small part of something that remains after the rest of it has been used, destroyed, or eaten

6. pulsar: 脉冲星
star that cannot be seen but can be detected by pulsating radio signals

7. wipe out
To remove, kill, or destroy completely

8. neutron star: 中子星
A celestial body consisting of the superdense remains of a massive star that has collapsed with sufficient force to push all of its electrons into the nuclei that they orbit, thus leaving only neutrons, and having a powerful gravitational attraction from which only neutrinos and high-energy photons can escape, rendering the body detectable only by x-ray.