Cosmic Collisions by zhangyun

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									Cosmic Collisions

    Josh Barnes
                  Stellar Collision




• A collision between the Sun and another star would take a few hours
• After, the Solar System would be a “disaster area”
                  Stellar Collision




• A collision between the Sun and another star would take a few hours
• After, the Solar System would be a “disaster area”
      How Improbable are Stellar Collisions?
In our wildly unfashionable arm of the Galaxy, stars are spread so far
apart that they almost never collide. The chance that the Sun will
collide with another star during its ten billion year lifetime is roughly two
to the power of thirty-two against - or about one chance out of four
billion. That's not impossible, but it is very improbable.

The chances of our colliding with a Black Hole are even lower.




                                In some parts of the Galaxy, stars are
                                much closer together, and the odds of
                                collisions are much higher.
                     Galactic Collisions
 Galaxy collisions happen all the time. The Milky Way has not had a major
 collision for over 10 billion years, but it is now swallowing a small galaxy, the
 Sagittarius dwarf. In a few billion years the Milky Way will begin colliding
 with our larger neighbor, the Andromeda galaxy




This pair of galaxies, known as
``The Mice'' because of their long
tails, are in the middle of a
collision.
           The Mice at Play




The two galaxies in The Mice first collided 170 million years ago,
and will merge about 300 million years from now.
           The Mice at Play




The two galaxies in The Mice first collided 170 million years ago,
and will merge about 300 million years from now.
How Dangerous are Galactic Collisions?

 Galactic collisions pose little threat to life. Planetary systems ride out
 collisions; their central stars may be launched into tidal tails or
 scattered in random directions, but gravity acts so gradually that
 planetary orbits are not disturbed.

 A collision takes about a billion years; during the last billion years, life
 on Earth evolved from single-celled organisms to amazingly primative
 apes who still think digital watches are pretty neat. Life forms evolving
 during the Milky Way's collison with Andromeda may enjoy the
 fireworks, but their worlds will not be demolished.



 So galactic collisions are mostly harmless, unless...
                 Merger to AGN
Unless the galaxies have supermassive black holes which ``feed'' on
interstellar gas and become active.
                 Merger to AGN
Unless the galaxies have supermassive black holes which ``feed'' on
interstellar gas and become active.
Conclusion:
Conclusion:

								
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