15 collisions 212 why should we not be surprised that

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15 Collisions 21.2
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Why should we not be surprised that galaxy collisions were common in the past? A. Galaxies moved faster in the past and therefore collided more often. B. Galaxies were larger in the past and therefore collided more often. C. The universe was much denser in the past, so its galaxies were much closer together, making collisions much more frequent. D. Because elliptical galaxies are formed by the collision of two spiral galaxies, ellipticals are observed to be more common in the past. 16
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Collisions were much more likely early in time because galaxies were closer together. 17 21.2
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Many of the galaxies we see at great distances (and early times) do look violently disturbed. 18 21.2
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The collisions we observe nearby trigger bursts of star formation. 19 21.2 Antennae (NGC 4038/4039)
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Modeling such collisions on a computer shows that two spiral galaxies can merge to make an elliptical. Spiral Galaxy + Spiral Galaxy = Elliptical Galaxy Process takes ~1.5 billion years 20 What Happens When Galaxies Collide? 21.2
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Milkomeda 21 Fun Fact: Andromeda Galaxy is moving toward us at 186,282 mi/hr, and it is 2.5 million ly away.
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Shells of stars observed around some elliptical galaxies are probably the remains of past collisions. 22 21.2
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Collisions may explain why elliptical galaxies tend to be found where galaxies are closer together. Gas can be stripped from a galaxy due to tidal forces which can create lenticular galaxies if stars have already been formed. 23 21.2
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Giant elliptical galaxies at the centers of clusters seem to have consumed a number of smaller galaxies . Central dominant galaxies 24 21.2
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Summary Galaxies can form from the cloud’s initial conditions or from collisions. 25
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What is a starburst galaxy ? A. a galaxy whose spiral arms have been stretched out into a star-like shape B. a galaxy with a supermassive black hole at the center C. a galaxy with a very high rate of star formation D. a galaxy with multiple supernovae E. a galaxy with a lots of gamma-ray emission 26
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Some galaxies, called starburst galaxies , are producing new stars at very high rates, as much as 100 times that of our galaxy!
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  • Fall '19
  • galaxy evolution

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