英语听力：自然百科 穿越银河系的旅行 Through Milky Way—13（在线收听） |
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 remains of these cosmic burps also litter our galaxy spiral arms, stars that die by shedding layers of elements.
Some layers are oxygen, and some layers are silicon, and some layers are sulfur, 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 Nebula, it gives a spectacular insight into how most stars end their lives. Our sun is destined to create a similar vista 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 Milky 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 metropolitan area.
As we get towards the heart of the Milky Way, the number of stars increases.
Though the density 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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| 原文地址：http://www.tingroom.com/lesson/zrbaike/2011/260159.html |