44
No black hole formed in a supernova can have a mass less than about three times that of the Sun, though. The core of the exploding star has to be at least this massive or else it only forms a neutron star, not a black hole. So don’t fret: the Sun cannot turn into a black hole.
45
Technically, this is a misnomer. It’s not a force, but a change in a force. Unfortunately, this term stuck, and that’s what we call it.
46
Also, the diameter of a black hole is proportional to its mass; double the mass and the black hole’s diameter doubles as well.
47
Yes, seriously, although a quick search didn’t yield any mention of the term in professional physics and astronomy journals.
48
Some black holes have been known to generate even higher-energy gamma rays as well, but this is due to nonthermal (not heat-related) processes.
49
As a reminder, a spectrum is created when you break up light into its individual colors, which can tell you lots of interesting things about the object that emitted the light.
50
Because black holes curve space, light gets bent as it travels near one—think of it as a road going around a curve, and a car on that road having to follow the curve too. An approaching black hole might be detected through this distortion—we might see star positions apparently changing, and bigger background objects like nebulae and galaxies getting smeared out. But this distortion is small when the black hole is far away, and likely to escape our notice until it is inside our solar system. And while this might give us decades of warning, there’s not a whole lot we could do about it short of evacuating the Earth . . . which presents its own set of issues.
51
At lower velocities, which are in general much more likely, the same events would unfold, just more slowly.
52
The force of gravity drops as the square of distance and goes up with mass. When the hole is √10 or about three times farther away from the Earth as the Sun, its gravity is times the Sun’s gravity.
53
Earthquake-induced floods are called tsunamis, which many people erroneously call tidal waves. In this case, we are literally talking about a wave caused by tides.
54
We ran across this before—it’s how stars make energy from fusion, via E = mc2.
55
You might think that the particle that fell in balances the mass from the particle that escapes, so the black hole has lost no net mass. However, because of the laws of gravity (and how weird they get inside a black hole), inside an event horizon a particle can actually have negative energy—essentially, the black hole holds on to it so tightly that the total energy of the particle is less than zero. This balances the positive energy of the particle outside the black hole, and everything remains even, except for the energy lost in separating the particles. Remember what I said earlier about common sense?
56
Actually, it’s not the whole truth. Black holes still may have something to say about our eventual fate; see chapters 8 and 9.
57
A relatively recent idea is that giant planets like Jupiter and Saturn may have formed from the direct collapse (called fragmentation) of material in the disk, rather than being built up by collision. This scenario is gaining some ground among astronomers, but the actual birth mechanism of planets is still somewhat debatable.
58
If you wish to view this as a cautionary tale, be my guest.
59
Before all this oxygen was exhaled by the new microbes, the Earth’s atmosphere contained a large amount of methane. Oxygen combines readily with methane, so most of the atmospheric methane was destroyed when oxygen became abundant. Methane is a strong greenhouse gas, so when it disappeared the Earth may have cooled significantly, gripping the planet in a global ice age. This would have aided any mass die-offs of bacteria as well.
60
It’s much more difficult to get meteorites from the inner planets out to Earth because they would have to fight the gravity of the Sun as well as that of their own planet. Despite that, some meteorites tentatively identified as being from Mercury have been found.
61
Panspermia is studied by many solid researchers with good reputations, but like any other field of science at the cutting edge of knowledge, it suffers from its share of kooks. Like UFO believers, there are people who point at everything they find as evidence of panspermia, from red-tinted rain in India to odd microbes found floating in the upper atmosphere. After looking into these cases, I have found them to exhibit the same problems as every other pseudoscientific claim: lack of solid observations, poorly controlled experiments, shoddy research, a lack of critical thinking, and a very strong tendency to jump (and leap, and catapult) to conclusions. We may yet find strong—even solid—evidence of life from space, but it will be uncovered using scientific methods: careful observations, reasoned experiments, and judicious thinking. Otherwise you just get cold fusion: a lot of pomp, but no circumstance.
62
As noted before, getting rocks from Earth to Mars is possible, but considerably more difficult and therefore much less likely.
63
This is easier if the wind is actually from a red giant; those kinds of stars emit far less UV radiation that can damage or kill the bacteria.
64
In fact, viruses are so simple that many scientists don’t consider them to be alive. Their lack of ability to reproduce on their own substantiates that (plus they don’t eat or excrete in any real sense either).
65
It’s possible that viruses were the precursors of life on Earth. They certainly have been around a long time, and coevolved with us. Even if life on Earth got its start from space viruses landing here via panspermia and kick-starting our ecosphere, such viruses would be harmless today. We’ve evolved for a long time since then, and it’s not terribly likely they will still find a lock to fit their key.
66
Incidentally, there is an even simpler structure than viruses, called prions. They aren’t much more than complex aggregations of proteins, and aren’t actually alive in any real sense. They can, however, mess up the structures of normal proteins in tissue, causing large holes to form in cells. This in turn produces all manner of horrifying problems, such as convulsions, dementia, and death—mad cow disease and scrapie in sheep are caused by prions. However, like viruses, they can attack only certain types of proteins, and any prions that evolved on another world are unlikely in the extreme to be able to infect terrestrial life.
67
I’m trying to be polite here. Cut me some slack.
68
The exact quotation is lost to antiquity; it may have been “Where is everybody?” which is just as pithy.
69
I discount UFO sightings. Despite a zillion blurry photos, obvious fakes, and shaky video, there has not been a single unequivocal piece of evidence that we have been visited by aliens, ever. Deal with it.
70
There is another way to be alone, as we’ll see in a moment.
71
This is serious: called Project Orion, it was studied in the 1960s. The acceleration isn’t smooth—getting kicked in the seat of your pants by a nuclear weapon generally isn’t—but it can build up tremendous speed. Unfortunately, the Nuclear Test Ban Treaty (chapter 4) forbids the testing of such a spaceship.
72
This logic means that a Star Trek—like galaxy—where there are lots of aliens at roughly the same technological level—is extremely unlikely. If life abounds in the Milky Way, civilizations are far more likely to be separated by gulfs of millions of years. Some of the aliens will be more like Q and the Organians (hugely advanced beings in the Star Trek universe), with one or two like us, and the rest not much more than extremely primitive microbes and yeasts. Another Star Trek aspect of this is the Prime Directive: the procedure to quarantine risi
ng civilizations until they develop the capability of interstellar travel. That’s an interesting idea, but I don’t buy it: it means that every single alien species out there will obey it. It only takes one maverick to spoil the secret.
73
You might think that maybe they were here, 65 million years ago, and pushed the dinosaur-killer asteroid our way. But remember, they’re advanced, smart, and without pity. A rock six miles across is pretty puny. They’d have dropped something a lot bigger on us, to make sure that in another few dozen million years, those little mammals crawling around the feet of the dinosaurs wouldn’t evolve into a spacefaring threat.
74
In the following sections, the number of years in the future should be considered approximate, perhaps accurate to a hundred million years or so.
75
You might expect that the Sun’s temperature is all that affects the Earth, but its size is important too. A ball bearing as hot as the Sun, for example, wouldn’t heat the Earth at all because it’s so small. Other factors in the Earth’s temperature include its distance from the Sun, its ability to shed heat (radiating it away at night), and even how rapidly it rotates. However, all of these factors can be accommodated mathematically to produce a model of the Earth’s temperature.
76
If you crunch the numbers, the average temperature of the Earth today at its current distance from the Sun should be just about or below the freezing point of water. It’s warmer on Earth, on average, because we have an atmosphere. The greenhouse effect keeps us nice and toasty . . . but, of course, too much of a good thing doesn’t help.
77
Actually, the Earth will be drier than bone, which is roughly 15 percent water by volume.
78
An interesting coincidence is that life has been around on Earth for 3.5 billion years (give or take), and will continue for another 3.5 billion. We’re currently right smack in the middle of the Age of Life on Earth . . . and any problems we have now may simply be chalked up to Earth experiencing a midlife crisis. ‡My suggestion: let go.
79
Some studies show that the core will shrink by about 100 feet per year or so, which is not a whole lot compared with the core’s size of many hundreds of thousands of miles across.
80
When you take a ball of clay and throw more clay on it, it gets bigger. If you take a ball of degenerate matter and throw more on it, weirdly, it gets smaller. Quantum mechanics, it cannot be said enough, is really freaky.
81
Even more if my wife just made cookies.
82
Currently, the Sun loses only about 10−14 (one one hundred-trillionth) of its mass every year. Obviously, this is an incredibly small number.
83
Many older books on astronomy say that the Earth will definitely be swallowed up by the Sun when it becomes a red giant, but those works don’t account for the Sun’s mass loss through its supersolar wind and the subsequent increase in the orbital diameters of the planets.
84
Remember, that’s the distance from the center of the Sun. The surface will be 50 million miles or so closer.
85
In reality, a bigger problem might be that all the plants on Earth have evolved to make oxygen using the color of sunlight we have now. A much redder Sun may be a much larger headache for our descendants than such a trivial thing as moving the Earth.
86
This is actually a terrifyingly close encounter. At closest approach the asteroid would be nearly as large in the sky as the full Moon—features on the surface would be easily visible to the naked eye—and be moving so rapidly that it would cross the sky in just a few minutes.
87
When the Sun loses mass, Jupiter will migrate outward as well, but we’ll also be stealing its energy, which moves it inward, so it’s hard to say just where it will end up.
88
Yes, assuming they have any. Or hands. Or heads.
89
Helium fusion under these circumstances has a rate that scales as the temperature to—hold on to your hat—the 40th power. This means a teeny-tiny increase in temperature causes the rate of fusion to accelerate insanely; a 20 percent rise in temperature increases the helium fusion rate by 1,500 times!
90
I hate to say it, but some calculations indicate that the white-dwarf Sun won’t be bright enough to ionize the expanding gas before the material disperses into interstellar space. It’s likely that when the Sun has this final fling, it will be too dark to see.
91
The planet in question, orbiting the red giant HD 17092, has a mass more than four times that of Jupiter, so it’s almost certainly a gas giant with no solid surface. Therefore, to be pedantic, the temperature is 900 degrees at the top of its cloud layer.
92
This may seem depressing to some, but it’s a relief to me: I’m not sure I want celestial neighbors capable of engineering on that scale.
93
The word galaxy comes from the Greek word galaxias, meaning milk, a reference to the Milky Way Galaxy. There is some confusion over the term Milky Way; sometimes it means the galaxy itself, and sometimes the milky stream of unresolved stars you can see from your backyard. Usually it’s clear in context.
94
Yes, this is the same analogy used for GRBs in chapter 4. Glad you noticed! The principle is the same, so I recycled it.
95
There are other sources of dust as well, including supernovae, but red-giant stars near the ends of their lives are the primary source.
96
Like the Earth’s atmosphere, the galactic disk fades away slowly with height above (and below) the plane, so an actual thickness is hard to determine. It also depends on how you measure it; bright, massive stars tend to stick near the galactic plane, while lower-mass stars can reach great heights. So the thickness changes with what kind of star you are using to trace it.
97
Neutron stars can be dangerous too. Some have incredibly strong magnetic fields, quadrillions of times stronger than Earth’s, which are generated inside the star and go out through the surface. A starquake—literally, like an earthquake on the star, but measuring a terrifying 30+ on the Richter scale—can shake the magnetic field violently, creating an ultra-mega-super-duper version of a solar flare. The energy released is enormous; in December 2004 such a flare from a magnetar 50,000 light-years away hit the Earth and actually had a measurable effect on our atmosphere. Magnetars are difficult to detect and incredibly rare (only a handful exist in the Milky Way), but they may in fact be the most dangerous objects in the galaxy. They’re the mob bosses of the Milky Way.
98
Most of the total mass of the Universe is made up of dark matter, a name scientists have hung on a type of invisible matter about which very little is known. Its existence is inferred by its effect on the normal, visible matter in galaxies, and it makes up something like 85 percent of all matter in the Universe. More is being learned about it every day, and one of the biggest goals in modern science is to determine the nature of dark matter.
99
At that distance, the Sun would be totally invisible to the naked eye; you’d need a telescope to see it at all.
100
Pronounced “thay-ta one cee ore-ee-ON-us,” if you want to impress your friends.
101
Assuming the Sun’s velocity through the nebula is the same as its orbital velocity around the galaxy of 140 miles per second.
102
We wouldn’t actually feel it, I’ll note, since even the thickest nebula is incredibly rarefied. The Earth wouldn’t slow in its orbit or anything like that. You’d hardly notice, except for the effects outlined above.
103
There might be a mitigating factor: the Sun will heat up the dust surrounding it, which will in turn warm up the Earth. The exact details of this, though, are difficult to calculate, and depend on lots of niggling factors,
such as the density of the cloud, its composition, and all that. Would the warm dust offset the darkening Sun enough to stop the glaciers from advancing? We simply don’t know.
104
More or less, that is. The planets themselves do have gravity, and they do affect one another, but only very subtly and only on very long time scales. We’ll be returning to this idea in a moment.
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.
Death From the Skies!: These Are the Ways the World Will End... Page 33