Death by Black Hole: And Other Cosmic Quandaries (7 page)

D
uring our everyday lives we don’t often stop to think about the journey of a ray of light from the core of the Sun, where it’s made, all the way to Earth’s surface, where it might slam into somebody’s buttocks on a sandy beach. The easy part is the ray’s 500-second speed-of-light jaunt from the Sun to Earth, through the void of interplanetary space. The hard part is the light’s million-year adventure to get from the Sun’s center to its surface.

In the cores of stars, beginning at about 10-million degrees Kelvin, but for the Sun, at 15-million degrees, hydrogen nuclei, long denuded of their lone electron, reach high enough speeds to overcome their natural repulsion and collide. Energy is created out of matter as thermonuclear fusion makes a single helium (He) nucleus out of four hydrogen (H) nuclei. Omitting intermediate steps, the Sun simply says:

Every time a helium nucleus gets created, particles of light called photons get made. And they pack enough punch to be gamma rays, a form of light with the highest energy for which we have a classification. Born moving at the speed of light (186,282 miles per second), the gamma-ray photons unwittingly begin their trek out of the Sun.

An undisturbed photon will always move in a straight line. But if something gets in its way, the photon will either be scattered or absorbed and re-emitted. Each fate can result in the photon being cast in a different direction with a different energy. Given the density of matter in the Sun, the photon’s average straight-line trip lasts for less than one thirty-billionth of a second (a thirtieth of a nanosecond)—just long enough for the photon to travel about one centimeter before interacting with a free electron or an atom.

The new travel path after each interaction can be outward, sideways, or even backward. How then does an aimlessly wandering photon ever manage to leave the Sun? A clue lies in what would happen to a fully inebriated person who takes steps in random directions from a street corner lamppost. Curiously, the odds are that the drunkard will not return to the lamppost. If the steps are indeed random, distance from the lamppost will slowly accumulate.

While you cannot predict exactly how far from the lamppost any particular drunk person will be after a selected number of steps, you can reliably predict the average distance if you managed to convince a large number of drunken subjects to randomly walk for you in an experiment. Your data would show that on average, distance from the lamppost increased in proportion to the square root of the total number of paces taken. For example, if each person took 100 steps in random directions, then the average distance from the lamppost would have been a mere 10 steps. If 900 steps were taken, the average distance would have grown to only 30 steps.

With a step size of one centimeter, a photon must execute nearly 5 sextillion steps to “random walk” the 70-billion centimeters from the Sun’s center to its surface. The total linear distance traveled would span about 5,000 light-years. At the speed of light, a photon would, of course, take 5,000 years to journey that far. But when computed with a more realistic model of the Sun’s profile—taking into account, for example, that about 90 percent of the Sun’s mass resides within only half its radius because the gaseous Sun compresses under its own weight—and adding travel time lost during the pit stop between photon absorption and re-emission, the total trip lasts about a million years. If a photon had a clear path from the Sun’s center to its surface, its journey would instead last all of 2.3 seconds.

As early as the 1920s, we had some idea that a photon might meet some major resistance getting out of the Sun. Credit the colorful British astrophysicist Sir Arthur Stanley Eddington for endowing the study of stellar structure with enough of a foundation in physics to offer insight into the problem. In 1926 he wrote
The Internal Constitution of the Stars
, which he published immediately after the new branch of physics called quantum mechanics was discovered, but nearly 12 years before thermonuclear fusion was officially credited as the energy source for the Sun. Eddington’s glib musings from the introductory chapter correctly capture some of the spirit, if not the detail, of an aether wave’s (photon’s) tortured journey:

The inside of a star is a hurly-burly of atoms, electrons and aether waves. We have to call to aid the most recent discoveries of atomic physics to follow the intricacies of the dance…. Try to picture the tumult! Dishevelled atoms tear along at 50 miles a second with only a few tatters left of their elaborate cloaks of electrons torn from them in the scrimmage. The lost electrons are speeding a hundred times faster to find new resting-places. Look out! A thousand narrow shaves happen to the electron in [one ten-billionth] of a second…. Then…the electron is fairly caught and attached to the atom, and its career of freedom is at an end. But only for an instant. Barely has the atom arranged the new scalp on its girdle when a quantum of aether waves runs into it. With a great explosion the electron is off again for further adventures.
(p. 19)

 

Eddington’s enthusiasm for his subject continues as he identifies aether waves as the only component of the Sun on the move:

As we watch the scene we ask ourselves, can this be the stately drama of stellar evolution? It is more like the jolly crockery-smashing turn of a music-hall. The knockabout comedy of atomic physics is not very considerate towards our aesthetic ideals…. The atoms and electrons for all their hurry never get anywhere; they only change places. The aether waves are the only part of the population which do actually accomplish something; although apparently darting about in all directions without purpose they do in spite of themselves make a slow general progress outwards.
(pp. 19–20)

 

In the outer one-fourth of the Sun’s radius, energy moves primarily through turbulent convection, which is a process not unlike what happens in a pot of boiling chicken soup (or a pot of boiling anything). Whole blobs of hot material rise while other blobs of cooler material sink. Unbeknownst to our hardworking photons, their residential blob can swiftly sink tens of thousands of kilometers back into the Sun, thus undoing possibly thousands of years of random walking. Of course the reverse is also true—convection can swiftly bring random-walking photons near the surface, thus enhancing their chances of escape.

But the tale of our gamma ray’s journey is still not fully told. From the Sun’s 15-million-degree Kelvin center to its 6,000-degree surface, the temperature drops at an average rate of about one one-hundredth of a degree per meter. For every absorption and re-emission, the high-energy gamma-ray photons tend to give birth to multiple lower-energy photons at the expense of their own existence. Such altruistic acts continue down the spectrum of light from gamma rays to x-rays to ultraviolet to visible and to the infrared. The energy from a single gamma-ray photon is sufficient to beget a thousand x-ray photons, each of which will ultimately beget a thousand visible-light photons. In other words, a single gamma ray can easily spawn over a million visible and infrared photons by the time the random walk reaches the Sun’s surface.

Only one out of every half-billion photons that emerge from the Sun actually heads toward Earth. I know it sounds meager, but at our size and distance from the Sun it totals Earth’s rightful share. The rest of the photons head everywhere else.

The Sun’s gaseous “surface” is, by the way, defined by the layer where our randomly walking photons take their last step before escaping to interplanetary space. Only from such a layer can light reach your eye along an unimpeded line of sight, which allows you to assess meaningful solar dimensions. In general, light with longer wavelengths emerges from within deeper layers of the Sun than light of shorter wavelengths. For example, the Sun’s diameter is slightly smaller when measured using infrared than when measured with visible light. Whether or not textbooks tell you, their listed values for the Sun’s diameter typically assume you seek dimensions obtained using visible light.

Not all the energy of our fecund gamma rays became lower-energy photons. A portion of the energy drives the large-scale turbulent convection, which in turn drives pressure waves that ring the Sun the way a clanger rings a bell. Careful and precise measurements of the Sun’s spectrum, when monitored continuously, reveal tiny oscillations that can be interpreted in much the same way that geoseismologists interpret subsurface sound waves induced by earthquakes. The Sun’s vibration pattern is extraordinarily complex because many oscillating modes operate simultaneously. The greatest challenges among helioseismologists lie in decomposing the oscillations into their basic parts, and thus deducing the size and structure of the internal features that cause them. A similar “analysis” of your voice would take place if you screamed into an open piano. Your vocal sound waves would induce vibrations of the piano strings that shared the same assortment of frequencies that comprise your voice.

A coordinated project to study solar oscillating phenomena was carried out by GONG (yet another cute acronym), the Global Oscillation Network Group. Specially outfitted solar observatories that span the world’s time zones (in Hawaii, California, Chile, the Canary Islands, India, and Australia) allowed solar oscillations to be monitored continuously. Their long-anticipated results supported most current notions of stellar structure. In particular, that energy moves by randomly walking photons in the Sun’s inner layers and then by large-scale turbulent convection in its outer layers. Yes, some discoveries are great simply because they confirm what you had suspected all along.

Heroic adventures through the Sun are best taken by photons and not by any other form of energy or matter. If any of us were to go on the same trip then we would, of course, be crushed to death, vaporized, and have every single electron stripped from our body’s atoms. Aside from these setbacks, I imagine one could easily sell tickets for such a voyage. For me, though, I am content just knowing the story. When I sunbathe, I do it with full respect for the journey made by all photons that hit my body, no matter where on my anatomy they strike.

I
n the study of the cosmos, it’s hard to come up with a better tale than the centuries-long history of attempts to understand the planets—those sky wanderers that make their rounds against the backdrop of stars. Of the eight objects in our solar system that are indisputably planets, five are readily visible to the unaided eye and were known to the ancients, as well as observant troglodytes. Each of the five—Mercury, Venus, Mars, Jupiter, and Saturn—was endowed with the personality of the god for which it was named. For example, Mercury, which moves the fastest against the background stars, was named for the Roman messenger god—the fellow usually depicted with small and aerodynamically useless wings on his heels or his hat. And Mars, the only one of the classic wanderers (the Greek word
planete
means “wanderer”) with a reddish hue, was named for the Roman god of war and bloodshed. Earth, of course, is also visible to the unaided eye. Just look down. But terra firma was not identified as one of the gang of planets until after 1543, when Nicolaus Copernicus advanced his Sun-centered model of the universe.

To the telescopically challenged, the planets were, and are, just points of light that happen to move across the sky. Not until the seventeenth century, with the proliferation of telescopes, did astronomers discover that planets were orbs. Not until the twentieth century were the planets scrutinized at close range with space probes. And not until later in the twenty-first century will people be likely to visit them.

Humanity had its first telescopic encounter with the celestial wanderers during the winter of 1609–10. After merely hearing of the 1608 Dutch invention, Galileo Galilei manufactured an excellent telescope of his own design, through which he saw the planets as orbs, perhaps even other worlds. One of them, brilliant Venus, went through phases just like the Moon’s: crescent Venus, gibbous Venus, full Venus. Another planet, Jupiter, had moons all of its own, and Galileo discovered the four largest: Ganymede, Callisto, Io, and Europa, all named for assorted characters in the life and times of Jupiter’s Greek counterpart, Zeus.

The simplest way to explain the phases of Venus, as well as other features of its motion on the sky, was to assert that the planets revolve around the Sun, not Earth. Indeed, Galileo’s observations strongly supported the universe as envisioned and theorized by Copernicus.

Jupiter’s moons took the Copernican universe a step further: although Galileo’s 20-power telescope could not resolve the moons into anything larger than pinpoints of light, no one had ever seen a celestial object revolve around anything other than Earth. An honest, simple observation of the cosmos, except that the Roman Catholic Church and “common” sense would have none of it. Galileo discovered with his telescope a contradiction to the dogma that Earth occupied the central position in the cosmos—the spot around which all objects revolve. Galileo reported his persuasive findings in early 1610, in a short but seminal work he titled
Sidereus Nuncius
(“the Starry Messenger”).

ONCE THE COPERNICAN
model became widely accepted, the arrangement of the heavens could legitimately be called a
solar
system, and Earth could take its proper place as one among six known planets. Nobody imagined there could be more than six. Not even the English astronomer Sir William Herschel, who discovered a seventh in 1781.

Actually, the credit for the first recorded sighting of the seventh planet goes to the English astronomer John Flamsteed, the first British Astronomer Royal. But in 1690, when Flamsteed noted the object, he didn’t see it move. He assumed it was just another star in the sky, and named it 34 Tauri. When Herschel saw Flamsteed’s “star” drift against the background stars, he announced—operating under the unwitting assumption that planets were not on the list of things one might discover—that he had discovered a comet. Comets, after all, were known to move and to be discoverable. Herschel planned to call the newfound object Georgium Sidus (“Star of George”), after his benefactor, King George III of England. If the astronomical community had respected these wishes, the roster of our solar system would now include Mercury, Venus, Earth, Mars, Jupiter, Saturn, and George. In a blow to sycophancy the object was ultimately called Uranus, in keeping with its classically named brethren—though some French and American astronomers kept calling it “Herschel’s planet” until 1850, several years after the eighth planet, Neptune, was discovered.

Over time, telescopes kept getting bigger and sharper, but the detail that astronomers could discern on the planets did not much improve. Because every telescope, no matter the size, viewed the planets through Earth’s turbulent atmosphere, the best pictures were still a bit fuzzy. But that didn’t keep intrepid observers from discovering things like Jupiter’s Great Red Spot, Saturn’s rings, Martian polar ice caps, and dozens of planetary moons. Still, our knowledge of the planets was meager, and where ignorance lurks, so too do the frontiers of discovery and imagination.

CONSIDER THE CASE
of Percival Lowell, the highly imaginative and wealthy American businessman and astronomer, whose endeavors took place at the end of the nineteenth century and the early years of the twentieth. Lowell’s name is forever linked with the “canals” of Mars, the “spokes” of Venus, the search for Planet X, and of course the Lowell Observatory in Flagstaff, Arizona. Like so many investigators around the world, Lowell picked up on the late-nineteenth-century proposition by the Italian astronomer Giovanni Schiaparelli that linear markings visible on the Martian surface were
canali.

The problem was that the word means “channels,” but Lowell chose to translate the word badly as “canals” because the markings were thought to be similar in scale to the major public-works projects on Earth. Lowell’s imagination ran amok, and he dedicated himself to the observation and mapping of the Red Planet’s network of waterways, surely (or so he fervently believed) constructed by advanced Martians. He believed that the Martian cities, having exhausted their local water supply, needed to dig canals to transport water from the planet’s well-known polar ice caps to the more populous equatorial zones. The story was appealing, and it helped generate plenty of vivid writing.

Lowell was also fascinated by Venus, whose ever-present and highly reflective clouds make it one of the brightest objects in the night sky. Venus orbits relatively near the Sun, so as soon as the Sun sets—or just before the Sun rises—there’s Venus, hanging gloriously in the twilight. And because the twilight sky can be quite colorful, there’s no end of 9-1-1 calls reporting a glowing, light-adorned UFO hovering on the horizon.

Lowell maintained that Venus sported a network of massive, mostly radial spokes (more
canali
) emanating from a central hub. The spokes he saw remained a puzzle. In fact nobody could ever confirm what he saw on either Mars or Venus. This didn’t much bother other astronomers because everyone knew that Lowell’s mountaintop observatory was one of the finest in the world. So if you weren’t seeing Martian activity the way Percival was, it was surely because your telescope and your mountain were not as good as his.

Of course, even after telescopes got better, nobody could duplicate Lowell’s findings. And the episode is today remembered as one where the urge to believe undermined the need to obtain accurate and responsible data. And curiously, it was not until the twenty-first century that anybody could explain what was going on at the Lowell Observatory.

An optometrist from Saint Paul, Minnesota, named Sherman Schultz wrote a letter in response to an article in the July 2002 issue of
Sky and Telescope
magazine. Schultz pointed out that the optical setup Lowell preferred for viewing the Venutian surface was similar to the gizmo used to examine the interior of patients’ eyes. After seeking a couple of second opinions, the author established that what Lowell saw on Venus was actually the network of shadows cast on Lowell’s own retina by his ocular blood vessels. When you compare Lowell’s diagram of the spokes with a diagram of the eye, the two match up, canal for blood vessel. And when you combine the unfortunate fact that Lowell suffered from hypertension—which shows up clearly in the vessels of the eyeballs—with his will to believe, it’s no surprise that he pegged Venus as well as Mars with teeming with intelligent, technologically capable inhabitants.

Alas, Lowell fared only slightly better with his search for Planet X, a planet thought to lie beyond Neptune. Planet X does not exist, as the astronomer E. Myles Standish Jr. demonstrated decisively in the mid-1990s. But Pluto, discovered at the Lowell Observatory in February 1930, some 13 years after Lowell’s death, did serve as a fair approximation for a while. Within weeks of the observatory’s big announcement, though, some astronomers had begun debating whether it should be classified as the ninth planet. Given our decision to display Pluto as a comet rather than as a planet in the Rose Center for Earth and Space, I’ve become an unwitting part of that debate myself, and I can assure you, it hasn’t let up yet. Asteroid, planetoid, planetesimal, large planetesimal, icy planetesimal, minor planet, dwarf planet, giant comet, Kuiper Belt object, trans-Neptunian object, methane snowball, Mickey’s dim-witted bloodhound—anything but number nine, we naysayers argue. Pluto is just too small, too lightweight, too icy, too eccentric in its orbit, too misbehaved. And by the way, we say the same about the recent high-profile contenders including the three or four objects discovered beyond Pluto that rival Pluto in size and in table manners.

TIME AND TECHNOLOGY
moved on. Come the 1950s, radio-wave observations and better photography revealed fascinating facts about the planets. By the 1960s, people and robots had left Earth to take family photos of the planets. And with each new fact and photograph the curtain of ignorance lifted a bit higher.

Venus, named after the goddess of beauty and love, turns out to have a thick, almost opaque atmosphere, made up mostly of carbon dioxide, bearing down at nearly 100 times the sea level pressure on Earth. Worse yet, the surface air temperature nears 900 degrees Fahrenheit. On Venus you could cook a 16-inch pepperoni pizza in seven seconds, just by holding it out to the air. (Yes, I did the math.) Such extreme conditions pose great challenges to space exploration, because practically anything you can imagine sending to Venus will, within a moment or two, get crushed, melted, or vaporized. So you must be heatproof or just plain quick if you’re collecting data from the surface of this forsaken place.

It’s no accident, by the way, that Venus is hot. It suffers from a runaway greenhouse effect, induced by the carbon dioxide in its atmosphere, which traps infrared energy. So even though the tops of Venus’s clouds reflect most of the Sun’s incoming visible light, rocks and soils on the ground absorb the little bit that makes its way through. This same terrain then reradiates the visible light as infrared, which builds and builds in the air, eventually creating—and now sustaining—a remarkable pizza oven.

By the way, were we to find life-forms on Venus, we would probably call them Venutians, just as people from Mars would be Martians. But according to rules of Latin genitives, to be “of Venus” ought to make you a Venereal. Unfortunately, medical doctors reached that word before astronomers did. Can’t blame them, I suppose. Venereal disease long predates astronomy, which itself stands as only the
second
oldest profession.

The rest of the solar system continues to become more familiar by the day. The first spacecraft to fly past Mars was
Mariner 4,
in 1965, and it sent back the first-ever close-ups of the Red Planet. Lowell’s lunacies notwithstanding, before 1965 nobody knew what the Martian surface looked like, other than that it was reddish, had polar ice caps, and showed darker and lighter patches. Nobody knew it had mountains, or a canyon system vastly wider, deeper, and longer than the Grand Canyon. Nobody knew it had volcanoes vastly bigger than the largest volcano on Earth—Mauna Kea in Hawaii—even when you measure its height from the bottom of the ocean.

Nor is there any shortage of evidence that liquid water once flowed on the Martian surface: the planet has (dry) meandering riverbeds as long and wide as the Amazon, webs of (dry) tributaries, (dry) river deltas, and (dry) floodplains. The Mars exploration rovers, inching their way across the dusty rock-strewn surface, confirmed the presence of surface minerals that form only in the presence of water. Yes, signs of water everywhere, but not a drop to drink.

Something bad happened on both Mars and Venus. Could something bad happen on Earth too? Our species currently turns row upon row of environmental knobs, without much regard to long-term consequences. Who even knew to ask these questions of Earth before the study of Mars and Venus, our nearest neighbors in space, forced us to look back on ourselves?

TO GET A
better view of the more distant planets requires space probes. The first spacecraft to leave the solar system were
Pioneer 10
, launched in 1972, and its twin
Pioneer 11,
launched in 1973. Both passed by Jupiter two years later, executing a grand tour along the way. They’ll soon pass 10 billion miles from Earth, more than twice the distance to Pluto.

When they were launched, however,
Pioneer 10
and
11
weren’t supplied with enough energy to go much beyond Jupiter. How do you get a spacecraft to go farther than its energy supply will carry it? You aim it, fire the rockets, and then just let it coast to its destination, falling along the streams of gravitational forces set up by everything in the solar system. And because astrophysicists map trajectories with precision, probes can gain energy from multiple slingshot-style maneuvers that rob orbital energy from the planets they visit. Orbital dynamicists have gotten so good at these gravity assists that they make pool sharks jealous.