Death from the Skies!
Page 34
105 Provocative in the literal sense as well, since these findings have provoked a flurry of papers both supporting and attacking their conclusions. I want to stress again that this periodicity in mass extinctions has not been verified, and may in fact not be real. Time will tell as more work is done.
106 The size of the actual energy source was known to be small because of some complicated physics involving how rapidly the source changed brightness—the bigger it is, the slower it can vary its output. Rapid fluctuations in the energy emission from 3C273 and other quasars made it clear that the source of their prodigious energy must be on the same scale as our solar system—tiny when compared to an entire galaxy.
107 Some very distant quasars have SMBHs estimated to have as much as 10 billion solar masses, but these have yet to be confirmed.
108 Because light travels at a finite speed, we see a distant object as it appeared in the past. It takes light 8.3 minutes to get to us from the Sun, so we see it as it was 8.3 minutes ago. We see a galaxy 10 billion light-years away as it was when the Universe was very young, only a few billion years old. In effect, telescopes are time machines. In reality—and as usual when dealing with relativity, time, and space—the situation is more complicated than this, but it’s not terrible to think of distance (in light-years) as equal to time (years in the past).
109 There is one other spiral in the group, called M33 or the Pinwheel galaxy. Although it’s a spiral like the Milky Way and Andromeda, it has only a fraction of the mass, so it’s not a big player like us.
110 Actually, many of the other galaxies in the Local Group are bound to us as well, but again, they are much smaller.
111 To be specific, this should say “collisions between large galaxies.” Big galaxies eat small ones all the time; the Milky Way is cannibalizing two dwarf galaxies right now. Both have been torn apart by the galaxy’s gravity, and their stars are slowly becoming integrated with the original Milky Way population. This has happened many times in the past as well.
112 One prediction of Einstein’s relativity is that merging black holes will actually cause a ripple in the fabric of space and time, like taking a bedsheet and frantically whipping it up and down. However, the gravitational waves resulting from two SMBHs merging are probably not strong enough to have any real effect on stars and other matter around them.
113 On the other hand, you can argue that since the Universe is all there is, everything there is, then the explosion happened everywhere all at once, and so it was big. That’s just semantics, though.
114 That means 0.0000000000000000000000000000000000000000001 second old.
115 To paraphrase the great philosopher-scientist Nigel Tufnel from This Is Spinal Tap: “How much more north could it be? The answer is none. None more north.”
116 Anything’s possible.
117 Literally, the creation of new nuclei, new elements.
118 A little math: Like gravity, the brightness of a star decreases with the square of the distance to the star—double the distance to a star and it will appear one-quarter as bright. But if stars are distributed evenly throughout the Universe, you’re basically adding up all the light from stars at a given distance from you, and they form the surface of a sphere. The area of the surface of a sphere depends on the square of its radius. So brightness drops with the distance squared, and the number of stars goes up with the distance squared—canceling each other out.
119 I am using the word theory as a scientist means it: a set of ideas so well established by observations and physical models that it is essentially indistinguishable from fact. This is different from the colloquial use that means “guess.” To a scientist, you can bet your life on a theory. Remember, gravity is “just a theory” too.
120 Light reflecting off water and metal can get polarized as well. Sunglasses that are polarized can block just the type of light waves that are aligned in that way, greatly reducing the glare of light reflected off cars and puddles.
121 Gas does get recycled in galaxies: stars explode, other stars lose mass in a stellar wind, and so on. It’s possible in some galaxies that stellar birth may continue for as long as another trillion years, but those are the exceptions, not the rules. In a trillion years or so, star formation will effectively cease.
122 In fact, it’s exactly like that: gas in a dwarf circulates in precisely this manner.
123 In reality, the explanation of this is far more complicated and involves invoking Einstein’s theory of relativity. I’ll spare you that and just leave you with the treadmill analogy, which is close enough.
124 Remember, as discussed earlier, that space can expand faster than the speed of light. The distant galaxies aren’t really moving faster than light; the space in between the galaxy and us is expanding such that it appears the galaxy is moving faster than light. Think of it as the track on the treadmill stretching as you’re running on it.
125 I’m at a loss for a name for this galaxy . . . MilkLocalGroupeda? Androgroupyway?
126 There are some theories stating that, depending on what’s driving the acceleration, the Universal expansion may overwhelm gravity. Eventually, all of space will stretch, including space in between bound gravitational objects. If that’s the case, then the horizon will continue to move in while space stretches. Eventually, everything will stretch—galaxies, stars, planets, even atoms. At some point, everything will get torn asunder as space itself shreds apart. For some reason, scientists call this idea the Big Rip. This turn of events seems pretty unlikely given what we know about the Universe, but it’s something to consider.
127 There will still be planets; they will orbit white dwarfs and brown dwarfs, and probably many more will wander the Universe after being ejected from their home stars during planetary formation. However, planets don’t generate energy, so they aren’t of much interest to us here. They’ll be frozen solid.
128 Binary brown dwarfs are common: two brown dwarfs in orbit around each other. Owing to some weird effects of Einstein’s relativity, the orbits of the objects will slowly decay with time. For a typical pair, the two objects will collide after about 1019 years, which is in the Degenerate Era. A merging of two brown dwarfs this way will almost certainly create a disk of material around them in the same way as an off-center collision would. This may be a “common” event during this era.
129 Astronomers use the term collision to mean any encounter where two or more objects interact with each other through gravity, and not necessarily to mean direct physical contact like a car crash.
130 Unlike smaller black holes, which will tear a star apart because of tidal forces, a supermassive black hole’s tides are far, far smaller, so stars will get eaten whole. There will be no accretion disk, and so no light emitted by the consumption of a star. Eating gas clouds, on the other hand, still will cause the black hole cosmic indigestion.
131 We don’t have to wait that long to see one decay: if we collect enough together, say 1037 of them, then we should see one decay every year. This has been attempted, and still no protons have decayed while scientists watched. If the decay time is off by a little bit—say it’s 1038—then this makes the process more difficult to detect . . . but 1038 years is still small compared to the time we’re talking about in this chapter.
132 Or whatever non-proton-based food they eat while watching movies.
133 Because of the bizarre nature of degenerate matter, lower-mass objects actually increase in size when they lose mass, the opposite of what we expect. White dwarfs start out roughly the size of the Earth, but in 1039 years or more, they’ll actually expand to be as big as Jupiter.
134 This released energy mostly gets converted into sound (footsteps) and motion (momentum as you travel down).
135 Yes, I had to look up those two words.
ve.