英语听力：自然百科 穿越银河系的旅行 Through Milky Way—13
时间：2014-05-27 07:03:43
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（单词翻译）
In about four or five billion years, it will grow into a much bigger star, a star called a red giant. And that outer atmosphere of gases will be held so loosely by the sun at that time that the gases will be blown away gently in what I call a cosmic burp.
The
remains1 of these cosmic burps also litter our
galaxy2 spiral arms, stars that die by shedding layers of elements.
Some layers are oxygen, and some layers are
silicon3, and some layers are
sulfur4, and those are the different colors we see in the Hubble Space Telescope images.
Not far from our sun is a place where a star is dying, the Helix
Nebula5, it gives a spectacular insight into how most stars end their lives. Our sun is
destined6 to create a similar
vista7 when it too dies 5 billion years from now.
But this doesn’t happen in every neighborhood. At the center of the galaxy is a place of mystery where stars disappear altogether. It’s here we’ll venture next.
On the next stage of our journey through the
Milky8 Way, we are heading to the center of our galaxy.
If we were to take a trip from the spiral arms out where we are by the sun, down to the center of the galaxy, it will be an interesting trip. It will be very much like moving from the suburbs into the heart of a very busy
metropolitan9 area.
As we get towards the heart of the Milky Way, the number of stars increases.
Though the
density10 of stars is tremendous in the center of the galaxy, it’s about a billion times higher than out here by the sun.
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