Death from the Skies! (46 page)

A spectrum is what you get when you run light through a prism or a finely etched grating. The light is separated into its individual colors, like a rainbow. When measured very carefully, a wealth of information can be obtained about the source of the light, including its temperature, chemical composition, and for some objects, like galaxies and GRBs, even their distance.

Stretch your brain back to dim memories of high school math: the area of a sphere = 4π
r
²
.

Pronounced “ATE a CARE in Ay,” for those practicing at home.

Actually, Eta may be a binary star, two stars orbiting each other. There is so much glare and interference from all the material surrounding the star that astronomers still aren’t 100 percent sure.

These findings are still controversial. This is a new field of science, and the models are somewhat shaky. Still, if you take away anything, just remember that a nearby gamma-ray burst is
bad.

Get used to that. Your common sense is going to take a beating here.

This means that astronauts orbiting the Earth are
not
weightless because they are beyond Earth’s gravity; they feel weightless because they’re falling. When you are sitting in a chair, you feel gravity as pulling you down into the seat, which supports your weight. If there is nothing to support your weight, you don’t feel the force of gravity, so when you’re falling you feel weightless. This is why astronauts appear weightless in orbit (described as “free fall”). At the usual orbital height (300 miles or so) the Earth’s gravity is only about 10 percent weaker than it is on the surface. Think of it this way: if the Earth’s gravity weren’t pulling on the astronauts, they would go flying off into deep space!

That distance is about 700 million miles from the Earth, so you’ll be thrusting a long time: well over a thousand years. Better pack a lunch.

More specifically,
nonrotating
black holes are spherical. In reality, most black holes are created from rotating stars, and that rotation is amplified when the core of a star collapses into a black hole. Like any rapidly rotating object, black holes can bulge out at their equators from centripetal acceleration.

The event horizon is not the physical surface of a black hole. A black hole doesn’t really have a surface; as far as we can tell, the matter in the black hole has shrunk all the way down to a mathematical point with literally zero size, called the
singularity.
The event horizon is the point where, at some distance from the singularity, the escape velocity equals the speed of light. The matter forming the black hole basically has no size, while the event horizon can be many miles across. Like I said, black holes are weird.

The corollary to this is: if you want to age less, move around really quickly all the time so others see your clock as running more slowly. Or you can sit around reading books on black holes and other astronomical dangers, and others will see your clock as running just like theirs.

Just to be clear, mass and weight are different. Mass is a property of matter; you can think of it as how much matter there is, and we measure it in grams or kilograms. Weight is the force of gravity on that mass, and we measure it in pounds. A cannonball has the same mass whether it’s on the Earth or the Moon, but on the Moon it weighs one-sixth as much because gravity is one-sixth as strong; on the Earth 1 kilogram weighs 2.2 pounds, but on the Moon it weighs about 0.36 pound.

Actually, because of the physics of solid bodies, the truth is that the mass above you doesn’t pull on you at all, oddly enough. Newton was the first person to be able to work that out mathematically. Basically, once you are inside an object like the Sun, the only mass you need to worry about is from the stuff between you and the center.

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.

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.

Also, the diameter of a black hole is proportional to its mass; double the mass and the black hole’s diameter doubles as well.

Yes, seriously, although a quick search didn’t yield any mention of the term in professional physics and astronomy journals.

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.

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.

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.

At lower velocities, which are in general much more likely, the same events would unfold, just more slowly.

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.

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.

We ran across this before—it’s how stars make energy from fusion, via
E = mc
²
.

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?

Actually, it’s
not
the whole truth. Black holes still may have something to say about our eventual fate; see chapters 8 and 9.

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.

If you wish to view this as a cautionary tale, be my guest.

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.

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.

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.

As noted before, getting rocks from Earth to Mars is possible, but considerably more difficult and therefore much less likely.

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.

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).

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.

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.

I’m trying to be polite here. Cut me some slack.

The exact quotation is lost to antiquity; it may have been “Where is everybody?” which is just as pithy.

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.

There
is
another way to be alone, as we’ll see in a moment.

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.

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 rising 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.

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.