Cosmic Collisions (eBook)

Table of Contents 8
Prerace 10
Chapter 1 Galaxies: The Big Picture 12
'' Mapping the Milky way is much like trying to map a crowded, foggy city from a single vantage point inside the murk,'' 13
Discovery of the Milky Way 13
Measuring and Weighing the Milky Way 17
"Galaxies are islands floating in the large cosmic ocean, each filled with myriads of stars." 18
"A speck of dust near a rice grain in a disk one and a half times greater than the Moon's orbit-that's our place in the Milky Way!" 19
"The Great Debate was arguably as important to our world view as some of the discoveries made by the explorers at sea in the seventeenth century." 21
Other Island Universes 21
"The protagonists left the auditorium in New York without a resolution to the immensely important problem of the scale of the universe." 22
"The Milky Way is just one of many galaxies scattered throughout the universe." 23
Different Types of Galaxies 23
"These oddball galaxies were largely ignored by astronomers until the mid-1950s, but have since turned out to be crucial for our understanding of how galaxies evolve." 25
Spiral Galaxies 27
"In the currently favored picture of galaxy formation, called the merger hypothesis, present-day ellipticals formed as a result of merger between these earlier building blocks." 28
"The origin of the spiral structure has been a matter for vigorous discussion among scientists for decades." 30
"Despite the smooth, featureless appearance and the slower motion of their stars, elliptical galaxies are quite exciting dynamical systems." 34
Elliptical Galaxies 34
"The Atlas of Peculiar Galaxies was a pioneering attempt to solve the mystery of the bizarre shapes of galaxies observed." 39
Irregular and Peculiar Galaxies 39
"Astronomers are now convinced that the galaxy collisions play a fundamental role in establishing the many different galaxy shapes." 41
Chapter 2 How do Galaxies form and evolve? 44
"Galaxy clusters are the largest gravitationally bound object we know." 46
"The first galaxies formed within the first five percent of the universe's lifetime. Compared to an average human lifespan the universe had not yet reached school age." 48
In the Bebinning 48
"The creation of the supermassive black hole appears to play a key role in actively regulating the growth of a galaxy." 49
Evolution of Galaxies 49
Evolution of sprial Galaxies 49
"After the collision, the captured stars rock back and forth and form the faint shells just as water forms ripples when we toss a rock into a pond." 51
Evolution of Elliptical Galaxies 51
"The resulting galaxy is dominated by stars that orbit the center in a complex, and random, web of orbit, just the behavior we see in elliptical galaxies." 53
Chapter 3 Galaxy collisions 56
"Our usual impression of the starry night sky is that of a nearly motionless dome. A single human life span is just the blink of an eye on a cosmological time scale." 57
The First Observations 57
"During the early part of the Second World War, Homberg devised an extraordinarily clever experiment in a darkned barn in Sweden." 60
The First Simulations 60
"A major aspect of this extra star formation in colliding galaxies was only properly revealed when Hubble's sharp eyes were turned towards selected systems." 64
Star Birth 64
"A supermassive black hole located at a galaxy's core feeds on the gas and disrupted stars coming from the surrounding galaxy." 67
Feefing Black Holes 67
Chaptetr 4 The Colliding Galaxies Movie 74
" It is clear that much of the diversity of observed galaxy collisions is due in part to the varying angles we observe them from and different times in their lives at which we observe them." 75
" The outcome of a collision depends not only on how close the galaxies come to each other but also on how the approach angle and the spin of the galaxies align. " 80
" Just as a pebble thrown into a pond creats an outwardly moving circular wave,a propagating density wave is generated at the point of impact and spreads outward. " 83
Splashing Collisions 83
Messy Mergers 83
Galaxy Groups 86
" When two galaxies pass close by each other the gravatational force affecting the stars nearest to the approaching galaxy is vastly greater than that experienced by that stars at the other end." 88
Tidal Traumps 88
Destroying Dwarfs 91
Chapter 5 The End 94
Milkomeda, the End of the Milky Way 95
Chapter 6 Gallery 102
The Authors 139
Resources 141
Image Credits 142