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听力文稿 ( Transcript )
In January 2000, John Dubinski set out to calculate the final fate of our galaxy, the Milky Way, and that of our nearest neighbor, Andromeda.
The Andromeda galaxy is actually falling towards the Milky Way, which means there probably have some close encounter at some point in the future.
At the moment, Andromeda is moving towards us at 400,000 kilometers per hour and scientists think one day it will hit us. So Dubinski decided to work out what will happen to us in three billion years when the two galaxies finally collide. After a long and complex calculation, the result was a vivid picture of the impending collision. A detailed prediction of how the Milky Way will end.
The clouds of gas hit each other at these huge velocities, hundreds of kilometers per second, and that basically creates great shockwaves which move through the gas and heat it to great temperature.
At the heart of this maelstrom, the boiling gases hurl towards the two converging black holes. This kick-starts a violent dual feeding frenzy as the two monsters spiral towards each other.
And eventually those two independent black holes with their accretion discs will spiral together and merge themselves and form an even more massive black hole.
Two possible fates await us. If we are on one side of the galaxy when this clash happens, we could be thrown out into the emptiness of space- if we are lucky.
The second possibility is that we're on the other side of the galaxy at the time of the collision in which case we could be thrown right into the center of this chaos.
In the active center of the merging galaxy, the huge feeding black hole will trigger a giant stellar explosions and supernovae. This is bad news for Earth.
There could be a horrible catastrophe. The wave of radiation from the blast wave of the supernova would hit the atmosphere and boil it off in an instant. So the atmosphere would be gone, the seas would boil off into space and the Earth would be toast.
maelstrom: a powerful whirlpool
accretion disc: a disk of usually gaseous matter surrounding a massive celestial object (as a black hole) in which the matter gradually spirals in toward and accretes onto the object as a result of gravitational attraction
supernova: a star that undergoes a catastrophic explosion, becoming suddenly very much brighter.
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