Could this be the difference between Caprica and Dead Earth? Did the conflict between the humanoid Cylons and their Centurion creations result in the use of cobalt bombs for at least some of the attack on Dead Earth? Based on D’Anna’s decision to stay on Dead Earth to die, it would seem so; a place still radioactive 2,000 years later almost certainly had salted bombs used on it. Did the Significant Seven use neutron bombs for at least some of their attack on Caprica? Based on the Cylon presence in a relatively undamaged Caprica City soon after the attack, it would seem so. It makes sense. The Significant Seven Cylons have always been obsessed with the idea of moral behavior.
PART THREE
THE TWELVE COLONIES AND THE REST OF SPACE
CHAPTER 15
Our Galaxy
A galaxy is an ensemble of stars, multiple star systems, star clusters, nebulae, gas, and dust, bound together by gravity into a loose structure. The spectrum of galaxies ranges from dwarf galaxies with a few tens of millions of stars up to giant galaxies having upward of a trillion. The universe, for its part, contains hundreds of billions of galaxies.bi
Because our sun Sol is in the Milky Way Galaxy, we can see our Galaxy only from the inside, as a creamy band of light that splits the night sky in two. Without our knowledge of astrophysics, ancient people were free to make up their own stories about what it was. The Dogon people of Africa saw the Milky Way as a spine, a backbone holding up the skin of the night sky. The Lenni Lenape people of North America saw it as the smoke from the campfires of the braves who had gone over to the other side of death. It is the Greek image, however, that has stayed with us: the root of “galaxy” stems from their gala, meaning “milk,” a poetic description of the river of white in the night sky. The first known use of the term “Milky Way” in English literature was in a poem by Geoffrey Chaucer.bj
Approximately twenty-four hundred years ago, the Greek philosopher Democritus proposed that the bright band in the night sky might consist of numerous distant stars. Proof of this came two thousand years later when Galileo Galilei observed it with his simple telescope. For three centuries, scientists held that the Milky Way was the universe in its entirety. Hints to the contrary, however, came toward the end of the eighteenth century.
Charles Messier was a French astronomer interested in hunting comets. The predicted return of Comet Halley in 1759 set off a mania for comet discovery among the telescope-wielding natural philosophers of the day. Messier, still in his twenties, caught the bug. Comet-hunting was an arduous task, since undiscovered comets appear as dim, fuzzy spots in the telescope eyepiece. The problem was that telescopes in Messier’s day were not very good by today’s standard. Practically any object—galaxies, nebulae, globular clusters—could also appear as dim, fuzzy spots. In his hunt for comets, Messier repeatedly kept coming across the same fuzzy objects in the same parts of the sky. He began to catalogue these objects, not because he thought they were intrinsically interesting, but so he could remove them from his comet searches. In 1771 he published his first list of The Top 45 Annoying Objects That Are Not Comets (actually, it was called Catalogue des Nébuleuses et des Amas d’étoiles [“Catalog of Nebulae and Star Clusters”], which he later expanded to 110 objects). Today his list is simply called the “Messier Catalog,” and objects within it are given “M” numbers. The Lagoon Nebula (see chapter 24), for example, was given the designation M8; the nebula in Orion was called M42; and the “Great Spiral Nebula”bk in the constellation Andromeda was christened M31.1
Sam Anders and Kara Thrace
Sam Anders and Kara Thrace
Many of the Messier objects are star clusters: home to thousands or millions of stars. Galactic, or open, clusters are a loose gravitationally bound collection of a few thousand stars, and are usually found within the disk of a spiral galaxy. They usually are sibling stars, all born at roughly the same time from the same protostellar cloud. The best example of this is probably the Pleiades,bl a cluster of hot blue stars about 100 million years old, visible in the north autumn sky riding on the back of the constellation Taurus. Their connection is tenuous at best—a passing star, or even encounters between the stars of the cluster, can disrupt the gravitational bond, ejecting the siblings onto their own separate paths through the galaxy. Take a good look at the Seven Sisters while you still can; they won’t be together in a few hundred million years.
Globular clusters are spherical, and consist of many millions of stars that are all much more tightly gravitationally bound. Globular clusters normally orbit within the galactic halo—an extended, roughly spherical, region surrounding a galaxy like the Milky Way—though they can occasionally be found in the population of stars within the disk or galactic bulge.
Based upon his observations of the “spiral nebula” M31 in 1917, Heber Doust Curtis estimated that it was 490,000 light years away. Based upon this, Curtis became a proponent of the “island universe” hypothesis, which maintained that spiral nebulae are actually independent galaxies outside our own.
Astronomers were not universally in agreement; however, the matter was settled conclusively by Edwin Hubble in the early 1920s using the new Hooker Telescope at the Mount Wilson Observatory overlooking Los Angeles, the largest in the world at the time. Hubble observed that certain regular variable stars in our Galaxy could also be seen in other galaxies. By comparing the brightness of those faraway stars with nearby stars, Hubble calculated that M31—and many other galaxies—were too distant to be part of the Milky Way. He also measured the speed of these newly distant galaxies, and found that most galaxies are moving away from us (M31 being an exception), and the more distant galaxies are moving away faster. This implies that our universe is expanding.
An artist’s conception of the Milky Way.
PROTOPLANETARY DISKS: “THE HAND OF GOD” AND “SCAR”
The most famous one is perhaps the Millennium Falcon being chased by Imperial TIE fighters in The Empire Strikes Back—it’s the science fiction staple called “dogfight in the asteroid belt,” evading the enemy while massive boulders tumble in all directions, the slightest error meaning instant death, guaranteed to pump up the viewer’s adrenaline.
In the first-season episode “The Hand of God,” the original intent was to create a similar tone by using a similar setting. The Cylon tyllium mine/refinery was to be set on an asteroid immersed in an asteroid belt. The problem is, we only know one asteroid belt—our own—and the rocks there are much more widely spaced than is typically depicted in sci-fi shows. NASA routinely passes spacecraft through the solar system’s asteroid belt—Voyagers I and II, Galileo, Cassini, New Horizons, to name a few—with little fear of collision. With rare exceptions, it’s difficult even to see one asteroid from another in the asteroid belt.
There are other, more scientifically plausible ways to make this work. The mining colony could have been set in the ring system of a planet like Saturn (which has been done in both Star Wars Episode II: Attack of the Clones and Star Trek: Voyager), bm or even set in a protoplanetary disk.
The writers considered the latter option a better choice, but an interesting thing happened along the way—the emphasis of the episode changed. This happens fairly often with television episodes; what is considered “important” changes as the script is revised and improved. With all those changes, in the end we don’t know where the Cylon tyllium mine/refinery was set and, in the end, it doesn’t matter. Writers David Weddle and Bradley Thompson liked the protoplanetary disk idea, however, so it was recycled for the second-season episode “Scar.”
Let’s look at the formation of our own planetary system. (We’ll go into more detail on this in chapter 16, “A Star Is Born.”) As the cloud of hot gas circling a young Sol flattens into a disk, more material is “exposed,” and radiates its heat off into space more readily and cools. Close to the protostar, where it is still quite hot, the first elements to condense out of the gas are metals, since they have the highest melting points. bn As the disk cools, chemical reactions can occur, and du
st forms.
Somewhat closer to the protostar is a place where it is just cool enough for ices of water and other compounds to form. This distance, different for every star, is called its frost line. Actually, there are several frost lines around each star, discrete places that mark the inner limit where ices of different compounds like water, ammonia, methane, and carbon dioxide can form.
As the disk of gas, dust, and ices swirls around the protostar, random collisions between particles occur. Occasionally they stick together, creating bigger particles. Occasionally these bigger particles collide and stick to form grains of material. Before long, the grains stick together to form pebbles, and before long the pebbles stick together to form boulders. Enough of these small collisions create solid objects known as planetesimals,bo small planetary building blocks. Because of the protostar’s heat, planetesimals formed near the star were made of nothing but metals and rocks. Out past the frost lines, the planetesimals were a mix of metallic, rocky, and icy bodies. There was actually more solid material from which to build planets in the outer solar system.
Planetesimals collided to form larger objects called protoplanets. Then something interesting occurred. As the larger protoplanets grew more massive, they developed a fairly strong gravitational pull. Collisions were now no longer random, but the larger protoplanets attracted others. This led to a scenario that the UCLA Professor William M. Kaula once termed “capitalistic growth” (that is, the rich get richer). This caused more collisions, making the protoplanets even larger, which increased their gravitational pull, which caused still more collisions, and so on. It is also at this point where we have an excellent setting for an episode of Battlestar Galactica: big chunks of space rock colliding with one another (and with any Vipers that might be in the area).‹
Recent data from space-based observatories like the Hubble Space Telescope and the Spitzer Space Telescope tell us that our Galaxy is in the form of a spiral with two major arms radiating from a thick central bar, as well as several minor arms. The central bulge is approximately 16,000 light-years across. The entire Galaxy, from edge to edge, is 100,000 light-years across. In Battlestar Galactica, occasional mention is made of the “red line,” the distance a Colonial ship can jump and still be reasonably sure it will end up at the desired location. bp For a Colonial ship, the red line is on the order of five light-years. That means that, jumping as far as it reasonably can, it would take Galactica twenty-thousand jumps to cross the Galaxy—which would take a year and three months at thirty-three minutes per jump.
A galaxy similar to ours: NGC 5866.
The pinwheel appearance of a spiral galaxy gives the impression that it is spinning, which, in fact, it is. At a distance of 26,000 light-years from the galactic center, the solar system orbits the center of the Galaxy every 225 million years. While that duration is a mere blink in the cosmic time scale, the last time the solar system was in the same place in the Galaxy, the dinosaurs were just getting a foothold on this planet, and Earth had only one continent.
Viewed edge on, a spiral galaxy appears much wider than it is thick, and it is.
Still, the disk portion of our Galaxy is roughly 1,000 light-years thick. It would take two hundred red-line jumps to cross it top to bottom. The central bulge is significantly thicker, about 5,000 light-years. Given these numbers, a rough volume estimate of the Milky Way Galaxy is 32 trillion cubic light-years. Estimates of the number of stars in the Milky Way range from 200 billion to 400 billion.2 If we assume that there are 400 billion stars in the Milky Way, then on average there is one star in every 80 cubic light-years. Although the stellar density varies greatly within the Galaxy, the average distance between stars is just over five and a quarter light-years. That distance is more than a single FTL red-line jump, meaning that it’s not likely that a Colonial ship could jump from one star system directly to another. In less densely populated parts of the Galaxy, the actual distances between star systems might be much farther. This fact was echoed in the Battlestar Galactica series bible:Galactica’s universe is also mostly devoid of other intelligent life. Unlike [other science fiction series] crowded galaxies filled with a multitude of empires, ours is a disquieting empty place. Most planets are uninhabitable... When we do encounter a world remotely capable of supporting human life, it will be a BIG DEAL.bq
Given the size of our Galaxy, it’s not amazing that the Colonials took nearly three years to find Dead Earth. It’s amazing that they found Dead Earth at all, even with the Prophecies of Pythia guiding them.
CHAPTER 16
A Star Is Born
Start about five billion years ago—about nine billion years after the Big Bang. We’re in a nebula, a cloud of gas and dust, two thirds of the way out from the center of the Milky Way Galaxy. The cloud is vaguely spherical, about 480 trillion kilometers across. br
The cloud is big, but it’s not very dense. The wisps of gas in this nebula are so sparse, you can almost see through the cloud without any problem. Still, 965 quadrillion cubic kilometers of gas—even thin, wispy gas—is going to have an enormous amount of mass. This particular cloud has the mass of approximately 100 Suns. But it has none of the heat of the Sun. The temperature of the gas in this cloud is about -450 degrees F, almost as cold as space itself, so cold that it has almost no heat at all.
This cloud is extremely fragile. It will break if something bothers it. If the cloud passes too close to a star, or if a star passes too close to the cloud, or if a supernova explodes nearby, the cloud will either split apart into true nothingness, or it will collapse.
Let’s watch it collapse.
Some small disturbance in nearby space causes a distortion in the cloud. It could be a change in temperature as the cloud absorbs energy from a supernova, or a fluctuation in gas density as the gravity of a passing star swirls the gas into vortices, or any number of things. The distortion affects only one part of the cloud, and that’s enough. After a few thousand years, globules of gas, called dense cores, begin to form near where the cloud was disturbed. The cores are a little warmer than the rest of the cloud, but not by much, about -400 degrees F. It would be absurd to expect all the cores to be exactly the same size, and they’re not. One core is larger than the rest, and so has more gravitational attraction than the others. The gravity of the larger core pulls the smaller cores toward it. Pretty soon, one dense core has eaten all the others, consuming as much as one-quarter of the entire nebula.
Perhaps the cloud was the gaseous remnant from the explosion of an earlier star, and perhaps it retained some of the spin, the angular momentum of its progenitor star. Perhaps the disturbance that caused the nebula to collapse imparted some spin. Either way, something has caused the cloud to spin. It starts slowly at first, but like a figure skater who spins faster the closer she pulls her arms into her body, as the cloud collapses, the faster it spins. The cloud also rapidly flattens, from a spherical shape to a disk with a central bulge—a very similar shape to that of our own Galaxy. The disk is called a circumstellar disk or protoplanetary disk (see the sidebar, “Protoplanetary Disks: ‘The Hand of God’ and ‘Scar,’” in chapter 15).
This giant dense core, with as much mass as 25 Suns, is about one and a half trillion kilometers in diameter.bs Its density is still very low, but the core’s gravity strongly affects the rest of the nebula. Trillions upon trillions upon trillions of tons of dust and gas continue to fall from all directions toward the center of the dense core. As material falls from the outer fringes of the cloud toward the center under the gravitational attraction of the core, its rotation speeds up. As the gas and dust speed up, the cloud’s temperature increases, gravitational potential energy being converted to kinetic energy. Not all of the material in the circumstellar disk will fall into the central core; some of the material is orbiting too rapidly ever to fall in.
Rostin’s assistant Billy Keikeya.
President Laura Roslin.
After about 100,000 years, the core’s increasing gravity has pulled all of its gas and
dust into a vague sphere about 16 billion kilometers across. That’s still twice as big as our entire solar system. Light would take about fifteen hours to cross from one edge to the other. And with all that friction caused by the ceaseless gravitational pull, the core has warmed up to several thousand degrees. In fact, the core of the core, where the frictional heating was the highest, is giving off so much heat that the outward thermal pressure is starting to push against the inward force of gravity. The dense core is no longer just a dense core. It is now a protostar.
At this point, things start to happen pretty quickly. In only a few thousand years, the protostar collapses to about 450 million kilometers in diameter—slightly less than the orbit of Mars. The temperature inside the protostar is over 100,000 degrees Kelvin; the temperature outside is about 3,000 Kelvin, about half as hot as the surface of the Sun. The protostar is glowing red, but this red light is being produced by gravitational friction, not nuclear fusion, so the protostar is still not yet a star. To become a star, it has to contract even further. The protostar continues to collapse under its own gravity until it is smaller than Earth’s orbit, then smaller than the orbits of Venus and Mercury, growing even smaller, hotter, and denser. Finally, somewhere in this last stage of contraction, the temperature of the core rises to a few million degrees Kelvin. The protostar has become a star.
Even if the mass of this new star were the same as our Sun, the brand-new star wouldn’t be very Sun-like. Not yet. Newly born stars usually go through what scientists call the T Tauri phase of development. bt In this phase, the newborn stars act more like adolescents: they are extremely variable, being brighter on some days and dimmer on others, and their faces are covered in starspots. They are also “loud,” in that they have a kind of superstellar wind that blows away much of the remaining gas in their surrounding nebula. This gas can be “vacuumed” up by large planetary embryos—planetary cores—in the outer system, eventually to form gas planets. T Tauri stars continue to contract, and after about 100 million years the core gets hot enough for hydrogen atoms to fuse into helium. This reaction gives off tremendous amounts of energy, in essence turning the star fully on. At this point, the T Tauri star settles down and joins the main sequence of stars.
The Science of Battlestar Galactica Page 12
