Category Dreams of Other Worlds

In the 1960s, long before the Milky Way was known to have a supermassive black hole, violent activity was seen in the centers of some distant galaxies. The manifestations were gas motions a hun­dred times faster than would be seen in a normal stellar system, intense radio emission concentrated in a tiny region of the galactic nucleus, and radiation across the electromagnetic spectrum from radio waves to gamma rays. Some of the strongest X-ray sources in the sky are galaxies hundreds of millions of light-years away, which means they have an X-r ay emission thousands of times stronger than a galaxy like the Milky Way. Rapid variability of the radio, optical, and X-ray emission localized the intense activity to regions light-days across, only ten times bigger than the Solar Sys­tem. No star cluster can pack so much radiation into such a small volume; the only plausible explanation was a gravitational engine: a black hole.60

Imagine a city like Los Angeles viewed from high above in a helicopter, where every streetlight, every house light, and every car light is standing in for a star. There are probably 100 million lights in the greater Los Angeles area, so in this analogy each light rep­resents a thousand stars. Los Angeles is like the disk of a spiral galaxy. Now imagine a light one inch across in the city center that emits a hundred times more radiation than all the city lights put together. That’s the intensity of an active galactic nucleus. It would be clearly visible from an immense height, long after the individual lights in the city had faded from view. We can see an incredibly bright point of light but the surrounding galaxy is too faint to see. That’s a quasar.

Through the 1990s astronomers realized that every galaxy con­tains a black hole, with a mass that scales with the mass of the old stars in the center of the galaxy.61 Moreover, these black holes are not active most of the time, so are not feeding and spewing out the energy that makes them easy to detect. The Milky Way is a medium-size galaxy with a 4-million-solar-mass black hole that’s currently inactive. The brightest quasars harbor black holes a thou­sand times larger, or a few billion times the mass of the Sun. These extraordinary gravitational engines form and grow quite naturally as galaxies form and grow but steadily consume matter, and by occasional mergers. It’s remarkable that nature makes black holes spanning a factor of a billion in mass, from a few times the mass of the Sun to the mass of a small galaxy. Their sizes range by the same factor of a billion, but they all share the properties of having an event horizon and (it is supposed) a central singularity. Strange as it might seem, massive black holes do not represent an extremely dense state of matter. The size of the event horizon is proportional to mass, but the volume increases by the cube of the size, so the more massive a black hole is the less dense it is within the event horizon. The 3-billion-solar-mass beast at the heart of the elliptical galaxy M87 is not much denser than water! Modest density does not, however, reduce their intrinsic strangeness (figure 10.4).

Chandra has played a vital role in telling the story of supermas­sive black holes and their behavior. In nearby galaxies it has de­tected vast bubble-like cavities and wavelike ripples in hot gas near the center, signs of “blowback” from the central engine.62 X-rays provide evidence of repetitive explosive activity, where mass falls onto the black hole, sparking it into activity and triggering jets of high-energy particles, which then evacuate the nearby volume and starve the black hole until new material accumulates. In this way, a massive black hole can be inactive most of the time. Chandra has also seen binary black holes in the centers of merging galaxies.

In one case, two huge black holes are only 3,000 light-years apart and will merge in the next hundred million years, provoking a cataclysm of gravity waves and new activity and yielding a single galaxy with a larger black hole.63 This is direct evidence for the manner in which galaxies and their embedded black holes have grown by mergers and acquisitions over billions of years.

Black holes and galaxies evolve on cosmic timescales of billions of years, so to figure out how they change the strategy is to make deep surveys that capture the census of active and inactive black holes at a range of distances or redshifts. The Chandra Deep Field was stared at for 2 million seconds, over three weeks, to create the deepest X-ray image of the sky ever made. This deep field, covering a patch of sky smaller than a postage stamp held at arm’s length, is combined with a shallower but wider survey to tell the full story.64 One of us (CDI) has participated in this research, with a survey of active galaxies in a two square degree region that netted more than two thousand supermassive black holes, and showed their evo­lution in cosmic time. This survey was sensitive enough to catch feeble accretors and black holes similar in size to the one in the Milky Way.

The broad conclusion of these surveys is that star formation and black hole growth in a galaxy are tightly linked. The heavi­est black holes, a hundred million times the Sun’s mass or larger, ate voraciously in the first few billion years after the big bang, and have been grazing or fasting since then. Black holes ten to a hundred million times the Sun’s mass had a more well-regulated diet, and because they consume smaller proportions of their gas and dust early on, they continue to grow even today. X-rays are crucial to telling this story, since they can penetrate regions that would extinguish optical and ultraviolet radiation.65 The typical size of a galaxy forming a supermassive black hole of a particular mass reduces with cosmic time, so the biggest black holes formed first. Massive galaxies in the far-flung universe misspent their youths by building monstrous black holes. This result is appar­ently at odds with the hierarchical mode of formation of structure in the universe, where small objects form first and gradually grow into larger objects. This unexpected phenomenon has been called “downsizing.”66

A by-product of this research is the solution to an old mystery of the X-ray sky. When the first X-ray satellites took their data in the 1960s and 1970s they saw a faint diffuse glow that spanned the entire sky. This X-ray “background” was unexplained. Surveys with Chandra and XMM-Newton show that the background is ac­tually composed of a myriad of pinpoints of X-ray emission from active galaxies 3-8 billion light-years away. Also, a majority of the emission is from galaxies where the nuclear activity is shrouded by dust and would not have been visible to an optical telescope. These surveys have also shown that black holes in the most mas­sive galaxies are “green.” By comparing the available fuel with the energy required to evacuate cavities in the central regions, the ef­ficiency can be calculated. It’s high because the mass is accreted slowly and smoothly and the energy is extracted very close to the event horizon of the black hole. If a family car was as efficient as one of these supermassive black holes, it would get a billion miles to a gallon of gas.

Pivotal roles in science are often taken by outsiders. The “father” of the big bang model was a part-time lecturer at the Catholic University of Leuven when he published a paper in a journal that was little read outside Belgium. George Lemaitre was a Catho­lic priest who had moved from civil engineering into physics and astronomy. Einstein was initially skeptical, but at a seminar by Lemaitre in Princeton in 1935, he expressed his admiration for the beauty of the theory.

The other intellectual parent of the scientific theory of creation was a Russian emigre called George Gamow. This physicist was elected to the Academy of Sciences of the U. S.S. R. at the age of twenty-eight, the youngest person ever to gain that honor. With his student Ralph Alpher, he showed that the early hot universe could have produced the amount of helium we see, which is too much to have been produced by stars. Gamow jokingly had his colleague Hans Bethe listed on the paper so it would read Alpher-Bethe – Gamow, in a pun on the first three letters of the Greek alphabet; Bethe had no other role in the paper.14 In 1948, the same year, Gamow and Robert Herman predicted that the afterglow should have cooled down after billions of years, filling the universe with microwave radiation at a temperature of five degrees above abso­lute zero, or 5 K.15 However, nobody pursued the prediction, due in part to a lack of widespread awareness of the theory, and in part to the primitive state of microwave technology at the time.

The new theory was given its catchy name by Fred Hoyle in a BBC radio broadcast in 1949.16 Even though he advocated the rival “steady state” theory, which didn’t involve a hot and dense early phase for the universe, he claimed the label was descriptive and not pejorative. As Hoyle noted, with typically sardonic wit, the big bang was an audacious theory: the entire universe, holding enough matter to yield more than a trillion trillion stars in many billions of galaxies, somehow emerged instantaneously and without any precedent from an iota of space-time! Steady state theory called for the gradual creation of matter in the vacuum of space between the receding galaxies. Although spontaneous creation of matter was ad hoc physics, it seemed like a more modest proposition.

For fifteen years, the status of the theory remained tentative. The universal recession of galaxies certainly pointed to a time when the universe was smaller, denser, and hotter. The explanation of the fact that the universe is a quarter helium by mass (and 10 percent by number of atoms) was a success, but the difficulty of measuring cosmic abundances of other light elements meant no further progress could be made on testing this idea, called big bang nucleosynthesis. Counts of extragalactic radio sources indicated the population was evolving and argued against the steady state theory. The missing ingredient was a decisive observation that fa­vored the hot big bang. It came by accident in 1964 when two engineers working at Bell Labs in Holmdel, New Jersey, detected a microwave signal of equal intensity in every direction in the sky (figure 12.2). NASA’s Wilkinson Microwave Anisotropy Probe, or WMAP, is the illustrious descendant of this pioneering experiment.

Chandra has also weighed in on two of the profound mysteries of cosmology: the nature of dark matter and dark energy. These two components of the universe account for 95 percent of its be­havior, yet the physical basis for them is not known and is not part of standard physics. Dark matter outweighs normal matter by a factor of six and binds galaxies and clusters and stops them from flying apart, as well as causing the expanding universe to decelerate for most of the first two thirds of its existence. Dark energy dominates dark matter by a factor of three and has caused the cosmic expansion to accelerate in the most recent third of the universe’s existence.67

Dark matter and dark energy don’t interact strongly with nor­mal matter like the atoms in our bodies, so stealth and cunning must be used to ensnare them and measure them. In both cases the laboratories used are rich clusters of galaxies, consisting of thousands of galaxies moving swiftly under the action of gravity and a huge cloud of superhot gas, so energetic that it emits X – rays. In 2006, an object called the Bullet Cluster was used for a convincing demonstration that dark matter actually exists. In the Bullet Cluster, a bullet-shaped cloud of hundred-million-degree gas is produced by a high-speed collision between a large cluster and a smaller one. The hot gas was slowed by the collision, due to a drag force analogous to air resistance. By contrast, the dark mat­ter hardly interacted at all and sailed through during the collision, ending up on either side of the hot gas.68 This result would not have occurred unless weakly interacting dark matter dominated the mass of both clusters. In particular, alternate theories of grav­ity, conjured up to avoid needing dark matter, fail to explain the observations. It seems we have to live with dark matter.

Dark energy is even more ephemeral, announcing its presence (and ubiquity) only by the effect it has on the cosmic expansion. The long and hard search for independent evidence of its existence settled on clusters of galaxies. In a study that took nearly a de­cade to complete, researchers showed that rich clusters suffer from “arrested development.”69 It’s more difficult for clusters to grow when space is being stretched. By comparing the size and age of clusters with simulations of how they should grow under differ­ent conditions of cosmology, the results cement the interpretation of dark energy as a universal repulsive agent. They also rule out alterations to gravity theory and confirm that general relativity is a good description of the behavior of matter and radiation on large scales. The enigma of dark energy has not been solved, but its status as the biggest challenge in both physics and cosmology has been enhanced. Whether it is a black hole devouring a companion, massive black holes causing mayhem in the centers of galaxies, or clusters being pulled apart by the accelerating expansion of space, Chandra has provided data to illustrate the violence of the uni­verse we inhabit.

A result of these insights is a new sense of the power of gravity. Stars are powered by gravity, and gravity also governs the nature of the most compact and energetic objects we’ve ever discovered. Dark forces even govern the expansion of the universe. When we think of other worlds, we think of planets illuminated by stars, where any life that exists is beholden to the energy from the star. But in a fundamental sense, starlight is just the inefficient leakage of radiation from mass-energy conversion by fusion. The true source of the starlight is gravity—a star is a gravitational engine. Black holes and neutron stars have no light but they have intense gravity. While they seem alien and utterly different from our world, given suitable protection or adaptation living creatures might be able to live near these compact stellar husks, using gravity to power their dreams.

Scientific discovery rarely unfolds smoothly or predictably. Eight years before the theoretical prediction of relic radiation, Andrew McKellar measured the spectra of stars and discovered interstel­lar material that was excited to a temperature of 2.3 K.17 He had no explanation for the excitation, which is caused by the radia­tion from the big bang.18 While Gamow’s prediction of a universe bathed in cold, microwave radiation sat in the literature, several experimenters had the detection of the radiation within their grasp but either did not control systematic errors well enough or were not aware of the importance of the observation. Robert Dicke at Princeton was, and by 1964 he and his team were hot on the trail of the big bang signature. But as they were preparing a radiometer on the roof of the physics building they got a call from Bell Labs. “Boys, we’ve been scooped,” was Dicke’s memorable response.19 The Nobel Prize was awarded in 1978 to Arno Penzias and Robert Wilson of Bell Labs for their discovery.

What was the nature of the radiation that Penzias and Wilson detected? To understand this involves rewinding the history of the

universe to its very early epochs. The Hubble expansion is a lin­ear relationship between distance and recession velocity: more dis­tant galaxies are moving away from us quicker. Although at first glance this seems to imply that we have a privileged location in the universe, a hypothetical observer in another galaxy would see exactly the same relationship that Hubble saw. In a uniform three­dimensional expansion each observer thinks they are the center of the universe. Since all cannot be, none are. Nor can we see an edge to the universe, so we can’t place ourselves with respect to a boundary. The Copernican principle holds. There’s no discernable center to the universe.

Reversing the expansion projects to a time when all galaxies were on top of each other: the big bang. But a simple backward extrapolation overestimates the age of the universe because matter tugs on other matter, so the expansion rate has slowed since the earliest epochs. In an expanding universe model the major observ­able is redshift, a stretching of the radiation from distant galax­ies due to the expansion of space-time itself. Redshift is simply related to the factor by which the universe has expanded since the radiation was emitted. One plus the redshift is the expansion fac­tor. Ironically, the universe is easier to understand in early times. Before structure forms, the universe behaves just like a simple gas, where the temperature and the average density both increase going back toward the big bang. Once gas starts to collapse by grav­ity, the physics is very complex. Stars and galaxies started form­ing when the universe was about ten times smaller than it is now, about 13 billion years ago.20

Extrapolating further backward, there was a time when the uni­verse was much denser than it is now and hot enough that atoms were ionized. Electrons liberated from atomic nuclei interacted with radiation and stopped the photons from traveling freely. It was as if the universe was shrouded in an impenetrable fog. As the universe expanded and thinned out and cooled, it became trans­parent and radiation could travel without interruption. This spe­cial epoch is the earliest time we can “see” into the universe. In a big bang model, the background radiation comes from a time when the universe was a thousand times smaller than it is today, and a thousand times hotter. Infrared photons from 380,000 years after the big bang, when the temperature was about 3000 K, have been stretched a thousand-fold to become microwave photons in a vast and frigid universe with a temperature a little below 3 K.

The picture of the sky in microwaves is an extraordinary baby picture of the universe. Imagine as an adult that you were shown a picture of yourself a few hours old. Since those waves are from the universe as a whole, they permeate space and they travel in every direction through expanding space. There are trillions of relic photons from the big bang in any volume like that of one breath. However, their radiant intensity coming from any direction in space is only 0.00001 Watt or a ten-millionth of a light bulb.21 If you can find an old-fashioned image tube TV and tune it between stations so you see only static, about 1 percent of the white specks on the screen are interactions of the dots of phosphor with those microwaves.22 The big bang is all around us.

Human eyes, and all vertebrate eyes, are actually protrusions of the brain. Michael Sobel explains, “Embryological studies show that the eyes begin to develop very early as two small buds on the neural tube that eventually becomes the brain.”35 We often think of ourselves as the pinnacle of evolutionary adaptation, but the human eye is adapted to detect a very narrow slice of the overall electromagnetic spectrum. This is not at all accidental. Had our Sun been a brown dwarf, emitting most of its light as infrared, our eyes would likely be adapted to infrared wavelengths. Some animals and insects, in fact, can see in wavelengths altogether in­visible to us. Pit vipers have a sensory organ located near their eyes that allows them to detect infrared or thermal images of prey. But­terflies are thought to have a wide range of vision and can identify potential mating partners by ultraviolet markings on their wings. Bees, many types of fish, and some birds also see in ultraviolet light. Scientists have recently discovered that flowers and plants, when viewed in ultraviolet light, often display patterns invisible to us and color quite distinct from the color we see. By imaging flow­ers in ultraviolet light, scientists realized that the patterns revealed in ultraviolet apparently serve as “landing strips” or markers use­ful in guiding insects to pollinating portions of the flower.36

At least forty to sixty different types of eyes, with up to ten dis­tinct means of forming images, have independently evolved, from simple constructions like a patch of skin acting as a photorecep­tor, to the compound eyes of flies and spiders, to the sophisticated eyes of the hawk or squid. “The result is an enormous range of eye types using pin-holes, lenses, mirrors, and scanning devices in various combinations to acquire information about the surround­ing world,” write Land and Nilsson. “Not all eyes are paired and placed on the head: there are chitons with eyes spread over their dorsal shell, tube worms with eyes on their feeding tentacles and clams with eyes on the mantle edge.”37 Various cave-dwelling ani­mals, because of a lack of light, have evolved without eyes. Some lizards, frogs, and fish, though they have complex eyes, also sport at the top or back of the head a third eye, or parietal eye, that at the least can indicate the presence or absence of light caused by the passing of a predator’s shadow. Even such a rudimentary eye offers valuable survival information.

At the other end of the spectrum of eye development are box jellyfish that have twenty – four eyes of four different types, two of which are extremely similar to human eyes. Existing for 600­700 million years, jellyfish have survived five mass extinctions but they’re often incorrectly characterized as not having a brain. Re­searchers recently found that neurons in jellies occur in neuronal centers distributed throughout their bodies and that they purpose­fully navigate within their environment. Box jellyfish use the acute vision of their pseudo-human eyes to see under and above water in navigating to and from underwater mangroves in order to feed, as a story in the New York Times reports: “Not only are the eyes equipped with a cornea, lens and retina, as human eyes are, but they are also suspended on stalks with heavy crystals on one end, a gyroscopelike arrangement that ensures the eyes are focused un­erringly skyward. . . . Every morning they must return to the roots or risk starvation. They rise toward the surface and their upturned eyes scan the sky, until at last they spy the mangrove canopy.”38 Beyond even these complex eyes are those of the cephalopods, like the octopus or squid, believed to be the most sophisticated eyes on the planet. Cephalopods focus their eyes with fine movements of the lens, unlike vertebrates, and they can automatically keep their pupils horizontal and even sense the polarization of light.

Above all scientific projects, the Hubble Space Telescope encapsulates and recapitulates the human yearning to explore distant worlds, and understand our origins and place in the universe. Its light grasp is 10 billion times better than Galileo’s best spyglass, and many innovations were needed for it to be realized: complex yet reliable instruments, the ability for astronauts to service the tele­scope,1 and the infrastructure to support the projects of thousands of scientists from around the world. The facility and its supporters experienced failure and heartache as well as eventual success and vindication.

Hubble’s legacy has touched every area of astronomy, from the Solar System to the most distant galaxies. In the public eye, it’s so well known that many people think it’s the only world-class astronomy facility. In fact, it operates in a highly competitive land­scape with other space facilities and much larger telescopes on the ground. Although it doesn’t own any field of astronomy, it has made major contributions to all of them. It has contributed to Solar System astronomy and the characterization of exoplanets, it has viewed star birth and death in unprecedented detail, it has paid homage to its namesake with spectacular images of galaxies near and far, and it has cemented important quantities in cosmology, including the size, age, and expansion rate of the universe.2

Ranked by size of the mirror, Hubble wouldn’t make it into the top fifty largest optical telescopes.3 Its preeminence is based on three factors associated with its location in Earth orbit. The first

is liberation from the blurring and obscuring effects of the Earth’s atmosphere. Ground-based telescopes typically make images far larger than their optics would allow because turbulent motion in the upper atmosphere jumbles the light and smears out the im­ages. Hubble gains in the sharpness of its vision by a factor of ten relative to a similar-sized telescope on the ground. Earth orbit also provides a much darker sky, which affects the contrast and depth of an image. The difference you might see in going from a city cen­ter to a rural or mountain setting is only part of the story; natural airglow and light pollution affect even the darkest terrestrial skies. A vacuum can’t obfuscate. The last feature of a telescope in Earth orbit is its ability to gather wavelengths of radiation that would be partially absorbed or even quenched by the Earth’s atmosphere. Hubble has taken advantage of this by working at infrared and ultraviolet wavelengths.

The Hubble Space Telescope (HST) is well into its third decade of operations, and it’s easy to take for granted the beautiful images that are released almost weekly. But it was not an effortless jour­ney for NASA’s flagship mission.

Observations of the cosmic microwave background rapidly im­proved, and it was soon found that the radiation had a spectrum almost perfectly consistent with one temperature, a type of radia­tion with what is called a thermal spectrum. This was additional support for its interpretation as relic radiation, because such a smooth spectrum only results from radiation that’s in equilib­rium with its surroundings. Since in this case the surroundings are the universe itself, thermal radiation is expected. Its temperature is 2.725 K and it is the most accurately measured temperature in nature.23

By the early 1970s, theorists had predicted that the microwave radiation should not be perfectly smooth. That’s because a slightly uneven distribution of matter causes very small variations in tem­perature, with denser regions hotter. The subtle variations in den­sity act as the seeds for later structure formation. Theories of gal­axy formation could not generate large lumps of matter without a little lumpiness with which to start. The initial variations are not really like “lumps” since they are physically extremely large and extremely shallow. In a purely metaphorical sense, the mighty oak trees that are present-day galaxies grew from the tiny acorns of anisotropy in the background radiation.

NASA’s Cosmic Background Explorer (COBE) was launched in 1989 to make more precise measurements of the microwave radia­tion than could be made from the ground or from high altitude bal­loons. COBE was cheap by modern standards, about $150 million, and extraordinarily successful. It confirmed the exquisite thermal nature of the spectrum, ruling out the last few remaining potential explanations other than a big bang. With only four years of data, the satellite was able to detect minute variations from smoothness; the radiation deviated from a constant temperature from one part of the sky to another by one part in a hundred thousand.24 These were the long-sought seeds of structure formation. Commentators and media pundits breathlessly embraced the story when project leader George Smoot talked about having discovered the “finger­prints of God.”25 Smoot and his colleague John Mather shared the 2006 Nobel Prize in Physics for their heroic work in advancing cosmology with the detection of these tiny fluctuations.

But there’s an extraordinary twist to this story. The smooth­ness of the microwaves and their perfectly thermal spectrum are difficult to explain in the standard big bang model because the universe was expanding so quickly early on. At the time the micro­waves were released, two points in space were receding at nearly sixty times the speed of light. Under these conditions, there’s no way disparate parts of the universe could come into equilibrium so adjacent patches of the sky shouldn’t be at exactly the same tem – perature.26 A related puzzle is the near-flatness of space. General relativity is based on curved space-time and it was expected that the vast mass of the universe would give an imprint of curvature. The cosmic background microwaves have traveled across the en­tire universe so should reveal if the space they’ve traveled through is curved. It’s not. To explain the smoothness of the radiation and the flatness of space, cosmologists have hypothesized a fantasti­cally early time, only 10-35 seconds after the big bang, when the en­tire universe expanded exponentially due to physics involved with the unification of three fundamental forces of nature. This event is called inflation.

Inflation modifies the big bang theory by positing that all we can see to the limit of vision of our telescopes—called the observ­able universe—is a small bubble of space-time that inflated to be­come large, smooth, and flat. The totality of space-t ime is very much larger, perhaps infinitely larger. Moreover, the variations in radiation that will grow to become galaxies are quantum fluctua­tions from a tiny fraction of a second after the big bang.27 It’s an extraordinary hypothesis.

The largest and most densely populated habitat on Earth is the ocean realm. As Claire Nouvian observes, “The deep sea, which has been immersed in total darkness since the dawn of time. . . forms the planet’s largest habitat.” Zoologists and oceanogra­phers are far from documenting the welter of sea life. “Current estimates about the number of species yet to be discovered vary between 10 and 30 million,” writes Nouvian. “By comparison, the number of known species populating the planet today, whether terrestrial, aerial, or marine, is estimated at about 1.4 million.”39 Down-welling light, whether sunlight or moonlight, in the upper reaches of the ocean’s water column can reveal an animal’s loca­tion or hideout. To avoid predators, marine animals largely forage for food at night, under cover of darkness. The result is that the ocean’s water column is the site of the largest daily animal migra­tion known, with marine animals migrating vertically as much as tens of meters to a kilometer. Harbor Branch Oceanographic Insti­tute scientist Marsh Youngbluth explains:

Each evening and morning all the oceans and even the lakes of the world are a theater to mass movements involving billions and billions of creatures swimming from deep waters to the surface and then back again to a colder, darker world. . . . Sixty years ago, when ac­tive sonar was first available, captains of fishing vessels thought that the bottom was rising under the boat. This phenomenon, called the “vertical migration,” is the largest synchronized animal movement on Earth. . . . Like nomads in deserts, they move to and from the surface waters in search of an oasis: the first 100m of the sea, where the sun­light still penetrates, the “photic” zone, abounding with food. . . . The signal that triggers and resets this ritual is the daily waning and wax­ing of sunlight, so travel frequently starts at dusk and ends at dawn.40

Although the deep sea is one place sunlight cannot reach, light and vision are no less critical there than for landlocked creatures. The Spookfish, for instance, lives at 1,000 meters’ depth in cold, dark Pacific Ocean waters and has reflective telescopes for eyes.41 Spookfish weren’t exactly the first astronomers, but unlike any other vertebrates, their eyes include crystal mirrors that focus light on the retina. And some marine animals have evolved the equiva­lent of wearing Polaroid sunglasses—they can see polarized light, which assists in their discerning jellyfish and other nearly transpar­ent species moving through the water column.

Deep below the coral reefs, ocean animals produce their own light to see and lure prey, signal distress or otherwise communi­cate, attract a mate, repel and stun predators, and counter-shade themselves.42 Nouvian contends that bioluminescence is the most common mode of communication on the planet. Approximately 90 percent of all ocean animals produce or deploy biolumines­cence in some capacity. Also referred to as cold body radiation or “cold light,” nearly 98 percent of the energy used in generating this living light affords only a minimal release of heat, presumably to protect the luminescent organism from being detected by preda­tors who sense infrared.

Bioluminescence has evolved independently some forty to fifty times as a result of its clear survival advantages. While fireflies pro­vide the most familiar example, a handful of land-based organisms luminesce, including fly larvae as well as some earthworms, snails, mushrooms, and centipedes. In the ocean realm, bioluminescence is the rule rather than the exception. Ranking among the biolumi­naries are bacteria, snails, krill, squid, eel, jellies, sponges, corals, clams, sea worms, Green Lanternsharks, Megamouth Sharks, and an array of fish. Inhabitants of mid-water habitats luminesce at varying intensities to countershade themselves and blend in with down-welling light so informative in the ecology of the water col­umn. Lanternfishes, of which there are at least two hundred spe­cies, can illuminate photophores along the entire length of their bodies to provide counter shade. “Photophores are often highly evolved structures, consisting not only of a light-generating cell, but also a reflector, lens, and color filter,” explains Scripps Insti­tute oceanographer Tony Koslow. “Most photophores emit light in the blue end of the spectrum to match the wavelength of down – welling light.”43

Viperfish and deep-sea anglerfishes have attached to their bodies a kind of a fishing rod with a lighted lure that attracts sizable prey directly into their toothy mouths. Marine biologist Edith Widder notes other deployments of bioluminescence in the ocean depths:

There are many fishes, shrimps, and squids that use headlights to search for prey and to signal to mates. . . . And as with some cars, some headlights can be rolled down and out of sight when they are not in use—a handy way of hiding that reflective surface and allow­ing the fish to better blend into the darkness. Most headlights in the ocean are blue, which is the color that travels furthest through sea­water and the only color that most deep-sea animals can see. But there are some very interesting exceptions like dragonfish with red headlights that are invisible to most other animals but that the drag – onfish can see and use like a sniper scope to sneak up on unsuspect­ing, unseeing prey.44

Deep-sea prawns and some squid emit bioluminescent fluids to startle predators and evade being eaten. Koslow reports, “Some jellyfishes jettison bioluminescing tentacles before making their escape, much as a lizard may let go its still-writhing tail to oc­cupy its predator while effecting its escape.”45 Other jellyfish can spray their predators with a luminescent substance that makes the

Plate 1. More than a century after Per – cival Lowell mapped Mars, the Hubble Space Telescope turned its best camera onto the red planet, producing this true color image in March 1997, just after the last day of Martian spring in the northern hemisphere. Mars was near its closest approach to Earth, 60 million kilome­ters away (NASA/David Crisp and the WFPC2 Camera Team).

Plate 2. Mars as seen by the Viking 2 lander. Images like this dashed the more fevered speculation of Mars as a living planet stemming from Percival Lowell and subsequent science fiction; it was revealed as a frigid and arid desert with a tenuous atmosphere, where water cannot exist for more than a moment on the surface before evaporating (NASA/Mary Dale – Bannister, Washington University in St. Louis).

Plate 3. Artist’s conception of one of the Mars Exploration Rovers on Mars. Spirit and Opportunity each far exceeded their life expectancy and have performed at a very high level in the unforgiving conditions on the surface of Mars. The rovers were identical as pieces of hardware, yet had quite dif­ferent experiences and adven­tures. Opportunity has exceeded its design lifetime by a factor of more than 35 (NASA/Jet Propulsion Laboratory).

Plate 4. Victoria Crater at Meridiani Planum on Mars, which is about 730 meters in diameter. Opportunity spent over two years exploring the rim of the crater, occasionally venturing inside, and by mid-2011 had traveled over 20 miles across the Martian terrain. Opportunity had a lucky bounce on landing and extricated itself from the kind of sand dune that disabled Spirit (NASA/Jet Propulsion Laboratory).

Plate 5. The four Galilean moons of Jupiter, visited by the Voyager spacecraft in 1979. In decreasing size order, the moons are Ganymede, Callisto, Io, and Europa; Jupiter is not shown at the same scale. Ganymede is 5300 km in diameter. The spacecraft made many discoveries in the Jovian moon system, including volcanism on Io and a subsurface ocean on Europa (NASA Planetary Photojournal).

Plate 6. Attached to the body of each Voyager spacecraft is a gold-plated, copper phonograph record. The record contains musical selections, images, and audio greetings in many world languages, along with instructions on how to retrieve the information. The analog technology will be very durable in the far reaches of space (NASA/Jet Propulsion Laboratory).

Plate 7. An artist’s impression of a close-up view of Saturn’s rings.

The rings are thought to be made of material unable to form a moon because of Saturn’s tidal forces, or to be debris from a moon that broke up due to tidal forces. The particles are made of ice and rock and range in size from less than a millimeter to tens of meters across (NASA/ Marshall Image Exchange).

Plate 8. A panoramic view of Saturn’s moon Titan, from the Huygens lander during its descent to the surface in late 2005. In this fish-eye view from an altitude of three miles, a dark, sandy basin is surrounded by pale colored hills and a surface laced with stream beds and shallow bodies of liquid composed of methane and ethane (NASA/ESA/Descent Imager Team).

Plate 9. Stardust collected samples of a comet and interstellar dust samples using a particle collector with cells containing aerogel, which is an amorphous, silica-based material that is strong yet exceptionally light. Particles entered this solid foam at high speed and were decelerated and trapped. The spacecraft returned its samples to Earth in 2006 (NASA/Jet Propulsion Laboratory).

Plate 10. This composite image was taken of comet Wild 2 by Stardust during its close approach in early 2004. The comet is about 3 miles in diameter. Its surface is intensely active, with jets of gas and dust spewing millions of miles into space. This image is a hybrid: a short exposure captures the jet while a long exposure captures the surface features (NASA/Jet Propulsion Laboratory).

Plate 11. SOHO took this image of the Sun in January 2000. The relatively placid optical appearance belies the intense activity seen in this ultraviolet image, where a huge, twisting prominence has escaped the Sun’s surface. When these events are pointed at the Earth, telecommunications and power grids can be affected (NASA/SOHO).

Plate 12. This computer representation shows one of millions of modes of sound wave oscillations of the Sun, where receding regions are colored red and approaching regions are colored blue. The Sun “rings” like a bell, with many complex harmonics, and study of the surface motions can be used to diagnose the interior regions (NSO/AURA/NSF).

Plate 13. People have used the sky as a map, a clock, a calendar, and as a cultural and spiritual backdrop since antiquity. This celestial map was produced in the seventeenth century by the Dutch cartographer Frederick de Wit. Constellations and star patterns are unchanging from generation to generation, so the stars were seen as being eternal (Wikimedia Commons/ Frederick de Wit).

Plate 14. We live in a city of stars, seen here in a full-sky panorama of the Milky Way photographed from Death Valley in California. The ragged band of light represents a view through the disk of the spiral galaxy we inhabit, and Hipparcos has mapped out the nearby regions of the disk and parts of the extended halo (U. S. National Park Service/Dan Duriscoe).

Plate 15. This Spitzer Space Telescope image shows star formation around the Omega Nebula, M17. This Messier object is a nebulosity around an open cluster of three dozen hot, young stars, about 5,000 light-years away. Spitzer records information at invisibly long wavelengths, and the difference between the view in the infrared (top) and the optical (bottom) can be dramatic. Colors in the infrared view represent different temperature regimes, with red coolest and blue hottest (NASA/JPL – Caltech/M. Povich).

Plate 16. The Spitzer Space Telescope detected molecules of buckminsterfullerene, or “buckyballs,” in a nearby galaxy, the Small Magellanic Cloud. The first zoom shows the type of planetary nebula where the molecules were found, and the second shows the molecule structure, where sixty carbon atoms are arranged like a tiny soccer ball (NASA/SSC/Kris Sellgren).

Plate 17. NASA’s Great Observatories are multi-billion – dollar missions with complex instrument suites, designed to answer fundamental questions in all areas of astrophysics. Including the ground-based Atacama Large Millimeter Array (ALMA), they can diag­nose the universe at temper­atures ranging from tens to tens of billions of Kelvin (NASA/ CXC/M. Weiss).

Plate 18. The dying star that produced this great bubble of hot glowing gas was first noted by Tycho Brahe in 1572. A white dwarf detonated as a supernova when mass falling in from a companion triggered its collapse; the shock wave from the subse­quent explosion led to the blue arc. The surrounding material is iron-rich and highly excited iron atoms create spectral lines detectable at X-ray wavelengths (NASA/ CXC/Chinese Academy of Sciences/F. Lu).

Plate 19. Two images of a pillar of star birth, three light-years high, in the Carina nebula, about 7,500 light-years away. Images taken through different filters select different wavelength ranges, which are combined into “true color” composites, where the colors convey astrophysical information in either visible light or infrared waves. Images like this have turned nebulae, galaxies, and clusters into “places” that resonate in the popular imagination (NASA/ESA/ STScI/M. Livio).

Plate 20. This image of the towering gas columns and bright knots of young stars seen in the Eagle Nebula (M16) was probably the first Hubble Space Telescope image to achieve widespread public recognition. It was part of the inspiration for the Hubble Heritage project, which showcases a different high-impact color image on the web each month. New worlds are being born at the tips of these fingers of hot gas (NASA/ESA/STScI/J. Hester/P. Scowen).

Plate 21. This exquisitely accurate map of the microwave sky, a projection of the celestial sphere onto a plane, shows the universe when it was a tiny fraction of its present age. The temperature variation between red and blue “speckles” is about a hundredth of a percent. The tiny variations, on angular scales of about a degree, represent the seeds for galaxy formation. It took a hundred million years or so for gravity to form the first galaxies (NASA/WMAP Science Team).

Plate 22. WMAP has played a major role in pushing the big bang model to the limit. The current model of the expanding universe posits an early epoch of inflation or exponential expansion, and subsequent expansion governed in turn by dark matter, causing deceleration, and more recently, dark energy, which is causing acceleration. WMAP has ushered in an era of “precision” cosmology (NASA/WMAP Science Team).

Plate 23. The Mars Science Laboratory, named Curiosity, will be exploring Mars for at least two years, starting with its landing in August 2012. The rover is the size of an SUV, compared to the Mars Exploration Rovers, which are the size of a golf cart, and the earlier Pathfinder, which is the size of a go – kart. Curiosity will study the past and present habitability of Mars by a detailed geochemical analysis of its rocks and atmosphere (NASA/ JPL-Caltech).

Plate 24. This montage of 1,235 exoplanet candidates from Kepler shows the planets projected against their parent stars, giving an idea of how they are detected by the slight dimming of the star’s light. By the end of its mission, Kepler will have collected enough data to be sensitive to Earth-like planets in Earth-like orbits of their stars, many of which are expected to be habitable (NASA/ Kepler Science Team).

predator in turn visible to fish looking for a quick meal. Medical researchers are only beginning to realize what we might learn from deep-sea bioluminaries. Off Puget Sound in the Pacific Northwest live the Aequorea victoria jellyfish, from which Green Fluorescent Protein (GFP) was first derived and used to generate other fluo­rescing marker proteins crucial in cancer and brain research and invaluable to cell biology and genetic engineering.46 What zoolo­gists discover about the variety of species deploying biolumines­cence in the deep ocean can help astrobiologists anticipate the life – forms that might illuminate the icy oceans of Europa, or alien seas on exoplanets orbiting other stars. To that end, Spitzer and other telescopes nightly scour the skies in search of other worlds.

In 1946, Yale astronomy professor Lyman Spitzer wrote a paper detailing the advantages of an Earth-orbiting telescope for deep observations of the universe.4 The concept had been floated even earlier, in 1923, by Hermann Oberth, one of the pioneers of mod­ern rocketry. In 1962, the U. S. National Academy of Sciences gave its imprimatur to the idea, and a few years later Spitzer was ap­pointed chair of a committee to flesh out the scientific motiva­tion for a space observatory. The young space agency NASA was to provide the launch vehicle and support for the mission. NASA cut its teeth with the Orbiting Astronomical Observatory mis­sions from 1966 to 1972.5 They demonstrated the great potential of space astronomy, but also the risks—two of the four missions failed. We’ve already encountered Spitzer since he gave his name to NASA’s infrared Great Observatory. Spitzer worked diligently to convince his colleagues around the country of the benefits of such a risky and expensive undertaking as an orbiting telescope.

After the National Academy of Sciences reiterated its support of a 3-meter telescope in space in 1969, NASA started design stud­ies. But the estimated costs were $400-500 million and Congress balked, denying funding in 1975. Astronomers regrouped, NASA enlisted the European Space Agency as a partner, and the telescope shrunk to 2.4 meters. With these changes, and a price tag of $200 million, Congress approved funding in 1977 and the launch was set for 1983. More delays followed. Making the primary mirror was very challenging and the entire optical assembly wasn’t put to­gether until 1984, by which time launch had been pushed back to 1986. The whole project was thrown into limbo by the tragic loss of the Challenger Space Shuttle in January 1986. When the shuttle flights finally resumed, there was a logjam of missions so another couple of years slipped by.6

Hubble was launched on April 24, 1990, by the shuttle Discov­ery. A few weeks after the systems went live and were checked out, euphoria turned to dismay as scientists examined the first images and saw they were slightly blurred. The telescope could still do science but some of the original goals were compromised. Instead of being focused into a sharp point, some of the light was smeared into a large and ugly halo. This symptom indicated spherical aber­ration, and further in-flight tests confirmed that the primary mir­ror had an incorrect shape. It was too flat near the edges by a tiny amount, about one-fiftieth of the width of a human hair. Such was the intended precision of Hubble’s optics that this tiny flaw made for poor images.7 Hubble’s mirror was still the most precise mirror ever made, but it was precisely wrong.

The spherical aberration problem may be ancient history and in the rearview mirror now, but at the time it was a public relations nightmare for NASA. Its flagship mission could only take blurry images. Commentators and talk show hosts lampooned the tele­scope and David Letterman presented a Top Ten list of “excuses” for the problem on the Late Show with David Letterman.8 More seriously, the episode became fodder for case studies in business schools around the country. The fundamental error was the result of poor management, not poor engineering. The Space Telescope project had two primary contractors: Perkin-Elmer, who built the optical telescope assembly, and Lockheed, who built the support systems for the telescope. There was also a network of two dozen secondary contractors from the aerospace industry. The mission was jointly executed by Marshall Space Flight Center and God­dard Space Flight Center, whose relationship involved rivalry and was not always harmonious, with overall supervision from NASA Headquarters. Complexity of this degree can be a recipe for disas­ter without tight and transparent management, and clear commu­nication among the best technical experts.

When the primary mirror was being ground and polished in the lab by Perkin-Elmer, they used a small optical device to test the shape of the mirror. Because two of the elements in this device were mis-positioned by 1.3 millimeters, the mirror was made with the wrong shape. This mistake was then compounded. Two addi­tional tests carried out by Perkin-Elmer gave an indication of the problem, but those results were discounted as being flawed! No completely independent test of the primary mirror was required by NASA, and the entire assembled telescope was not tested be­fore launch, because the project was under budget pressure. Also, NASA managers didn’t have their best optical scientists and engi­neers looking at the test results as they were collected. The agency was embarrassed and humbled by the failure. Their official inves­tigation put it succinctly: “Reliance on a single test method was a process which was clearly vulnerable to simple error.”9 In this way a multi-billion-dollar mission was hamstrung by a millimeter-level mistake and the failure to do some relatively cheap tests. In the old English idiom: penny wise, pound foolish. The propagation of a small problem into a huge one recalls another aphorism from En­gland, where a lost horseshoe stops the transmission of a message and the result affects a critical battle: for the want of a nail, the war was lost.

Enter the Wilkinson Microwave Anisotropy Probe. WMAP was conceived as a way of pushing to a new level of precision and a new set of tests of the big bang theory. Most of those tests involve looking at anisotropies in the radiation, small variations in tem­perature from one part of the sky to another.

The all-sky map of microwave radiation has to have foreground emission from the Milky Way removed before it can be interpreted. There is a temperature gradient across the sky caused by the mo­tion of the Solar System relative to the universe as a whole at a speed of about 360 kilometers per second. The microwave sky is 0.00335 K warmer toward the direction of our motion and the same amount cooler in the direction opposite to our motion. That small signal is also modeled and subtracted out.28 What’s left is a mottled pattern of very low-level variations. COBE had enough sensitivity to detect the variations statistically, but with an angular resolution of 7 degrees (the angle of your outstretched fingers at arm’s length) it could not say much about the detailed structure of the radiation.

COBE was a small satellite that traveled in a 900-kilometer high orbit of the Earth. The instrument that measured temperature variations had two horn receivers pointing in different directions, with the satellite rotating every 70 seconds so they could sweep across the sky. WMAP was a much larger and more sophisticated satellite, even though it was a third the mass of COBE. It collected microwaves with a pair of 1.5-m dishes and its receivers detected the radiation in five frequency bands. It rotated every 130 seconds and made a complete map of the sky every six months. The satel­lite was launched in 2001 and sent to a Lagrange point (where the gravity of the Earth and Moon balance) 1.5 million kilometers from Earth, where the contaminating radiation is much lower than in low Earth orbit. As a result, WMAP was forty-five times more sensitive than COBE and it was able to resolve thirty-five times smaller regions on the sky, or two times smaller than the angle of the full Moon in the sky (plate 21). The large difference is com­parable to the gain of the Hubble Space Telescope over a one-foot diameter telescope of the ground.29

WMAP operated flawlessly for ten years, and the exciting re­sults of COBE and WMAP generated the momentum for a third – generation microwave satellite called Planck, named after the Nobel Prize-winning German physicist. Planck is primarily a Eu­ropean mission. Launched by ESA in 2009 to a location at the same Lagrange point as WMAP (L2), it improves on WMAP in both sensitivity and angular resolution.30