Death from the Skies! (47 page)

In the following sections, the number of years in the future should be considered approximate, perhaps accurate to a hundred million years or so.

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.

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.

Actually, the Earth will be
drier
than bone, which is roughly 15 percent water by volume.

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.

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.

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.

Even more if my wife just made cookies.

Currently, the Sun loses only about 10
⁻¹⁴
(one one hundred-trillionth) of its mass every year. Obviously, this is an incredibly small number.

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.

Remember, that’s the distance from the
center
of the Sun. The surface will be 50 million miles or so closer.

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.

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.

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.

Yes, assuming they have any. Or hands. Or heads.

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!

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.

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.

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.

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.

Yes, this is the same analogy used for GRBs in chapter 4. Glad you noticed! The principle is the same, so I recycled it.

There are other sources of dust as well, including supernovae, but red-giant stars near the ends of their lives are the primary source.

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.

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.

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.

At that distance, the Sun would be totally invisible to the naked eye; you’d need a telescope to see it at all.

Pronounced “thay-ta one cee ore-ee-ON-us,” if you want to impress your friends.

Assuming the Sun’s velocity through the nebula is the same as its orbital velocity around the galaxy of 140 miles per second.

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.

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.

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.

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.

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.

Some very distant quasars have SMBHs estimated to have as much as 10 billion solar masses, but these have yet to be confirmed.

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).

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.

Actually, many of the other galaxies in the Local Group are bound to us as well, but again, they are much smaller.

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.

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.

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.

That means 0.0000000000000000000000000000000000000000001 second old.

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.”

Anything’s possible.

Literally, the creation of new nuclei, new elements.

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.

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.

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.

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.

In fact, it’s
exactly
like that: gas in a dwarf circulates in precisely this manner.

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.

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.

I’m at a loss for a name for this galaxy . . . MilkLocalGroupeda? Androgroupyway?

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.