Category Dreams of Other Worlds

On Planets and Dwarfs

Somewhere in the twilight between stars and planets lie objects called brown dwarfs. Below about 8 percent of the Sun’s mass, physical conditions will never allow the fusion of hydrogen into helium, as happens in the Sun. There may be a flickering of en­ergy from the fusion of hydrogen into deuterium, but lower mass objects don’t have a sustainable source of energy. When they’re young, brown dwarfs are easy to observe in the infrared because they generate a lot of heat during their gravitational collapse. As they age, they get cooler and fainter. For example, a puny star 10 percent of the mass of the Sun would have a temperature of 3000 K and a luminosity 1/10,000 that of the Sun. By contrast, a brown dwarf 5 percent of the mass of the Sun would be three times cooler and a further 100 times dimmer. It would take a million of these feeble objects to equal the light of the Sun. Some astronomers con­sider Jupiter a failed star or a brown dwarf. Models indicate that brown dwarfs likely host moons like those of Jupiter and Saturn, worlds replete with weather systems, geysers, volcanoes, moun­tain ranges, and oceans—even if, as on Europa, the oceans are frozen over.

Set on a moon orbiting a gas giant planet in the nearby Alpha Centauri star system, James Cameron’s film Avatar (2009) mes­merized audiences with its rendering of Pandora orbiting a Jupiter- like world whose swirled and rippled clouds resemble those of Ju­piter and its Great Red Spot. Cameron’s Pandora (one of Saturn’s moons also happens to be named Pandora) abounds in colorful flora and fauna evocative of Earth’s ocean environments, like the giant Christmas Tree Worms that suddenly retract when touched, the seeds of the sacred tree that float with the pulses of a jelly­fish, and the photophores that dot the plants, animals, insects, and human-like inhabitants of Cameron’s adventure tale.58 That the Na’vi have blue skin seems no accident or random artistic choice. In ocean waters, blue light is least absorbed and can penetrate into the depths so that most deep-sea animals see solely in blue light. With the announcement in October 2012 of an exoplanet with a similar mass to Earth detected in the Alpha Centauri triple star system, Cameron’s fictional depiction seems even more plausible.59

In part, what captivated film audiences was the bioluminescence with which Cameron painted his Pandoran forests. Having ex­plored and documented deep ocean fauna in the film Aliens of the Deep (2005), Cameron is familiar with myriad bioluminescent sea life and readily projects similar plants and animals onto his imagi­nary world. Draped with waterfalls alight with bioluminescence, Pandora’s forests teem with glowing fireflies and whirling fan liz­ards. The forest floor is carpeted with illuminating moss, while its streambeds are lit with the equivalent of sea anemones. In effect,

Cameron anticipates how life might be adapted on an exomoon of a gas giant planet or a brown dwarf star. On such worlds, we might expect to find luminous biota highlighted with photophores as Cameron predicts or species with eyes better adapted to night or low-light conditions. Even as felines have dark-adapted vision superior to humans, the Na’vi have feline features and navigate the night-t ime forest with far better facility than the character Jake. Cameron’s bioluminescent world may have been inspired by Jules Verne’s 20,000 Leagues Under the Sea, in which the char­acters, strolling on the ocean floor, encounter bioluminescent jel­lyfish and note their “phosphorescent glimmers.” Actually, nearly all jellies in the deep sea are luminescent. Verne’s voyagers likewise chance upon corals, the tips of which glow. In stark contrast to the nineteenth-century perception that the ocean floor was devoid of life, Verne imagined the seafloor abounding in bioluminescence. An engraved illustration for 20,000 Leagues titled “On the ocean floor” depicts a kelp forest with large corals, crustaceans, and a flotilla of giant jellyfish whose bodies and tentacles radiate light (figure 9.6). Cameron’s vision of bioluminescent organisms flour­ishing on a nearby exomoon is similarly prescient.

Back on Earth, the first brown dwarf was discovered in 1995. Spitzer has contributed to this research by detecting some of the coolest and faintest examples known, including eighteen in one small region of sky sifted from among a million sources detected.60 Despite their extreme faintness, Spitzer can detect the coolest brown dwarfs out to a distance of one hundred light-years. The outer layers of these substellar objects are cool enough that they’re rich in molecules. The composition of the gas, and so the appear­ance of narrow lines that act as chemical “fingerprints” in the spec­trum, changes as the brown dwarf evolves. Most of the eight hun­dred cataloged brown dwarfs have atmospheres with temperatures in the range 1200°C to 2000°C. The next category, with tempera­tures from 1200°C down to 250°C, has strong methane absorp­tion in their atmospheres. There’s overlap (and often confusion) between planets and brown dwarfs because some giant exoplanets are larger and hotter than some brown dwarfs. The very coolest category of the brown dwarf, and the end point of their evolution, has recently been discovered. NASA’s Wide Field Infrared Survey

On Planets and Dwarfs

Figure 9.6. An original illustration from Jules Verne’s 20,000 Leagues Under the Sea depicting bioluminescence. A more modern media representation is in James Cameron’s 2009 motion picture Avatar, where bioluminescent creatures inhabit the exomoon Pandora, where the action takes place. On Earth, thousands of species of sea creatures of all sizes employ bioluminescence (Jules Verne’s 20,000 Leagues Under the Sea).

Explorer (WISE), which was launched in 2009, has finished a scan of the entire sky at infrared wavelengths. In 2011, astronomers reported six of the coolest stars ever found, one of which has a sur­face at no more than room temperature.61 The WISE data have the potential to reveal brown dwarfs closer than Proxima Centauri, the nearest star to our Sun.

Another promising mission in the search for dwarf stars and transiting exoplanets is headed by Harvard astronomer David Charbonneau and was designed largely by Philip Nutzman, an as­tronomer at the University of California, Santa Cruz. The MEarth Project is focusing eight small robotic telescopes on 2,000 M dwarf stars.62 The project targets particularly M dwarfs as they are smaller than the Sun and transiting planets would block out a greater portion of the star’s light, making them easier to detect. Studying nearby transiting exoplanets could afford astronomers a better sense of whether Earth-like planets are common and ad­ditionally allow astronomers to discriminate the chemistry of their atmospheres. Within six months of launching their project, the team detected their first transiting planet, a super-Earth named GJ 1214b in orbit around a star 13 parsecs from Earth.63 In 2010, the journal Nature reported that the atmosphere of GJ 1214b was found to be comprised either of water vapor, or of thick clouds or haze as on Saturn’s moon Titan.64 Infrared investigations are planned to determine which of these options exist on the planet. With resources like Zooniverse. org, in the coming decade the pub­lic will likely contribute to the search for biomarkers such as ozone or water vapor in the atmospheres of these other worlds.

Awash as it is in newborn stars and exoplanets, the universe may be teaming with life. Perhaps in some far future humans will have physical, robotic, or other means of virtual presence on a nearby exoplanet or one of its moons that, similar to Cameron’s Pandora, teems with bioluminescent life. Astronomer Carole Haswell cau­tions, “If any of this is to happen, however, we need to use our collective ingenuity to understand and repair the effects that our industrial activity and our burgeoning population are having on our own planet.”65 What we learn from exoplanets, Haswell sug­gests, might be invaluable in understanding Earth’s climate evolu­tion and in ensuring our own survival and that of our companion species. In the meantime, NASA and the astronomical community welcome the public’s contribution to one of humankind’s greatest adventures—locating possible habitable planets and, in time, the signatures of life in some dark and overlooked corner of the vast and silent wastes of interstellar space.

On Planets and Dwarfs

The Science in Hubbles Iconic Pictures

Kessler explains that some astronomers were initially dismissive of Hubble’s “pretty pictures.” They felt such images had less to do with science and that the public would accept the false color pho­tos as what Hubble actually sees. But as Kessler points out, Hubble was the vehicle for changing this perception, particularly in the case of the stunning images of the Eagle Nebula (M16) released in 1995 (plate 20). A group of astronomers at Arizona State Uni­versity led by Jeff Hester were interested in photo-evaporation, by which they suggested radiation from a massive star in the nebula is evaporating gaseous material away from sites of newly forming stars. Kessler notes that Hester’s team “did not plan the observa­tion with the intention of creating a visually impressive picture.”27 However, their remarkable image of the Eagle Nebula awed scien­tists and general audiences alike. And, as anticipated, in the nebu­la’s 10-trillion-kilometer gaseous columns, Hester’s team identified regions of newly forming stars.

Upon release of the Eagle Nebula images, Kessler reports, “The New York Times, Washington Post, USA Today, and other major newspapers printed articles featuring the image, and Newsweek, U. S. News and World Report, and Time all ran stories in the fol­lowing weeks.”28 Kessler highlights the fact that while the news reports detailed Hester’s theory regarding new star formation, the real emphasis of the news coverage was the spectacular beauty of the cloud pillars in the Eagle Nebula, subsequently dubbed the “Pillars of Creation.” A report in 1999 on Hubble’s popularity by the Space Telescope Science Institute indicates that “web hits at the time of the M16 release were about a half a million a month.”29 The fascination with Hester’s image of the Eagle Nebula demonstrated that stunning astronomical photos could capture both important scientific data and amazing spacescapes that readily communicate complex information to general audiences. Kessler points out that NASA quickly realized the tremendous public support for Hubble might be better served through an organization that would regu­larly request, produce, and release images taken by Hubble. The Hubble Heritage Project emerged out of such interest.

Commenting on what he and members of the Hubble Heritage Project were looking for in the composition of spectacular photos like that of the Eagle Nebula, Jeff Hester explains:

I want [people] to realize, when they look at images like that, that what they are looking at is humans acting on this urge within us. Going out there and proactively building the technology and the tools that allow us to reach out with our minds and our aesthetic and our imagina­tions and our sense of wonder and our sense of curiosity. . . . That these [photographs] are not just nicely aesthetic, but. . . testaments to what we as people are able to do. To take images of columns of clouds of gas and dust several thousand light years away in which stars are forming, and to bring them home and to make that part of the universe known to us, to extend the sphere of the human mind and imagination out to encompass those things.30

Hester nevertheless understands the difficulty in communicating complex scientific information:

[Science] demands a rigorous vocabulary, the vocabulary of math­ematics. It demands that you learn to think in that vocabulary. That’s not a vocabulary that’s accessible to a lot of people. . . . [I]t really mat­ters that you find a way to get around the vocabulary problem, that you find a way to bother to think about who it is that you’re talking to, what is it that they are familiar with . . . [so] that instead they can start to get their arms around [it] a little bit.31

The Hubble Heritage Project’s home page provides thumbnails of approximately two hundred images; these are the best of the best from among tens of thousands of images taken by the facility.32 Ac­cording to Kessler, the project was the brainchild of planetary sci­entist Keith Noll and astronomer Howard Bond. Along with Anne Kinney and Carol Christian, these scientists collaborated to create Hubble Heritage images to promote public education and general interest in astronomy and space science. Kessler contends that they have expertly achieved these goals by blurring the boundaries be­tween art and science to contribute to both astronomical investi­gation as well as popular understanding of cosmology. Keith Noll summarizes the project’s objective:

“[M]y real hope for this is that there are kids that have our pictures on their walls, that maybe spend some time dreaming about what it’s like to be in space, what it would be like to travel to these exotic places. . . . But what I really hope is that they all sort of carry this little bit of awe and mystery with them in their lives, so that everything isn’t just about getting up and driving in traffic and paying bills. It kind of helps to remember. . . how amazing the universe is.33

Hubble’s photos easily convey some of the most fascinating as­pects of star birth and death, and solar system formation. In many cases it doesn’t require specialized or scientific training to immedi­ately grasp the import of some of Hubble’s most remarkable im­ages. This is true for the Hubble photos of the Eagle Nebula and its collapsing gases in star birth regions, the newly forming star systems in the Orion Nebula (M42) with its proto-planetary disks the size of our Solar System, the star birth visible in the arms of the Whirlpool galaxy as illustrated in the mosaic of M51 (figure 11.2), or the bizarre and complex cloud formations produced by dying stars at the heart of planetary nebulae.

Perhaps the simplest reason for the Hubble telescope being so cherished is that in a single bound, complex scientific investigation can be conveyed in a handful of amazing images. The tremendous energy radiated as stars blow off their gaseous outer layers is evi­dent at a glance from a single image. While the average person may not have imagined the import of a star’s magnetic field in shaping planetary nebulae, the effects of intense radiation and stellar winds are nearly palpable in such photographs. In images with less obvi­ous information, a simple caption can make the meaning immedi­ately comprehensible to the nonspecialist. A short caption regard­ing the pillars of dust in the Eagle Nebula towering to 10 trillion

The Science in Hubbles Iconic Pictures

Figure 11.2. M51 is a nearby spiral galaxy called the Whirlpool galaxy; this is how the disk of the Milky Way would appear if we could gaze down on it, rather than being embedded in the disk. A nearby companion galaxy is triggering intense star formation in the spiral arms. Hubble Space Telescope can resolve individual bright stars in this galaxy (NASA/STScI/Hubble Heritage Team).

The Science in Hubbles Iconic Pictures

Figure 11.3. The Red Spider Nebula (NGC 6537) has waves of dust and gas extending a hundred billion kilometers. First cataloged by William Herschel over two hundred years ago, the subtle patterns are due to shock waves caused as outflowing material runs into the interstellar medium, a gas more sparse than the best vacuum on Earth (NASA/ESA/STScl/G. Mellema).

kilometers, or 6 trillion miles, or explaining that stellar winds in the Red Spider Nebula (NGC 6537) produce waves of dust and gas a hundred billion kilometers high (figure 11.3), while nearly incom­prehensible, has afforded general audiences unprecedented under­standing of the incredible energy and matter involved in star birth and death.34 Hubble images of gravitational lensing caused by large clusters of galaxies, majestic barred spirals whirling through space, and spectacular globular clusters have been indelibly etched into the public imagination. But beyond this popular appeal, the Hubble Space Telescope has generated enough unique data to qualify as the most successful scientific experiment in history.

Celestial Harmonies

The correlation between music and exploration of outer space is deeply rooted in the human psyche. The Greek mathematician Pythagoras was purportedly the first to show that musical notes, octaves, chords, and their harmonics were the product of simple mathematical ratios and whole numbers. The Pythagoreans real­ized that a string attached to an instrument produces a fundamen­tal tone when plucked. Halve the string and the tone will be an octave higher. Other harmonics, or overtones, occur at the third, fourth, fifth, seventh, and ninth divisions or intervals of the string. The Pythagoreans further posited that the universe itself could be understood in terms of this basic mathematics of music, and that the planets, for instance, would be distanced from the Sun in inter­vals similar to the intervals along a string that produce harmon – ics.43 By the early 1600s, German astronomer Johannes Kepler was also captivated by Pythagoras’s notion of a “music of the spheres.” He theorized in Harmonices Munde (The Harmony of the World) that musical harmonies could be seen in the motion of planetary bodies. As physicist Amedeo Balbi explains, “Building on ideas by Pythagoras and Plato. . . Kepler was trying to give a scientific foundation to the concept of the ‘music of the spheres’, the idea according to which each planet moving around the Sun produces a definite sound.”44 Kepler suggested their orbits would be deter­mined by the mathematics of musical harmonics.

Stars, galaxies, even planets naturally produce electromagnetic energy, or low-energy radio emission, as they rotate and move through space. Several planets in our Solar System generate strong electromagnetic emissions from their powerful magnetospheres. In the 1970s, the Voyager spacecraft recorded Jupiter’s radio emis­sions. Of course, the human ear cannot detect sound in the empty vacuum of space. However, we can “hear” the whine of Earth and the eerie sounds of Saturn’s radio emissions via satellite recordings translated by computer programs that render measured frequen­cies as audible sound.45

Far more impressive are the acoustic tones of the Sun, as we learned in the chapter on SOHO. Astrophysicists are learning a great deal about the interior composition and physics of the Sun via helioseismology, by which astronomers track acoustic sound waves that travel through the entire body of the Sun. Amazingly, the Sun resonates with myriad sound waves that can be measured like musical notes that are directly analogous to fundamental tones and complex harmonic overtones. Turbulence at the top of the Sun’s convective zone segments the photosphere into granules, thousands of kilometers across, that pulse up and down. These pulses send sound waves careening through the body of the Sun and reveal a characteristic acoustic imprint at various internal boundaries like that between the convective and radiative zones.46 By recording the acoustic waves traveling through our Sun, astro­physicists have a far better understanding of the internal struc­ture of stars, the abundance of helium in our Sun revealing its age, the Sun’s rate of rotation, and how temperatures at the core compare to its million-degree corona. These internal acoustic waves also are associated with storms on the solar surface and are being used to predict future sunspots by detecting disturbances inside the Sun.47

Synesthesia is the experience of one sense being rendered as an­other so that you can taste a color or hear visual phenomena. Just as musicians were experimenting with electronic and psychedelic explorations of outer space, astronomers were documenting the Sun’s acoustic waves and experiencing their own synesthesia. In the case of the tonal resonances generated by the Sun’s pulsing surface, scientists can hear what they visually detect of this reso­nance. The first phase of helioseismology, launched from 1960 to 1979, interestingly emerged during the same period as the rise of electronic space music.


When we dream of other worlds, our dreams may be vivid and real and colorful, but they’re subject to the limitations of our senses. To visualize something, even if in our mind’s eye, we use the visual sense. For most of the history of astronomy we learned about the universe exclusively through visible light. Tens of thousands of years of naked-eye observations were followed by the first night time use of the telescope by Galileo in 1610, followed by a steady march of successively larger telescopes, culminating with the 8-11 meter behemoths of the present day, with dreams of even larger ones to come.1

The historical focus on visible light was natural, since the most powerful human sense evolved to match the peak energy output of our life-giving star. The cool outer envelopes of stars emit most of their radiation in the visible range, and galaxies are just assem­blages of stars. The night sky is visually rich. About 6,000 stars are visible to the naked eye at a dark site, but they are just an infini­tesimal sliver of the stellar plentitude of the universe. We live in a system of 400 billion stars, and the observable universe contains roughly 100 billion stellar systems, for a staggering total of 1023 stars.2 Also, the spectral transitions that are the fingerprints of dif­ferent types of atoms fall mostly in the visible wavelength range. Cosmic chemistry is practiced with telescopes that gather light and disperse it into its constituent wavelengths.

Nevertheless, just over two hundred years ago experiments showed there are wavelengths longer than the reddest waves of light and bluer than the bluest waves of light. A hundred years later, Wilhelm Rontgen performed the first systematic experiments to understand the nature of mysterious radiation that was gener­ated by high-energy particles moving in the vacuum of a sealed glass tube. In 1895, he announced the discovery of “X rays.” The details of the discovery are poorly documented because Rontgen had his lab notebooks burned when he died. X-rays electrified the scientific community and within a year their potential for medical imaging was realized. It was a lot longer before anyone discovered that they could be used for astronomy. Rontgen received the first Nobel Prize ever awarded for Physics in 1901.3

Just as X-rays provided a window into the human body, they now provide a window in space onto worlds barely imagined. X – ray telescopes have revealed the nature of black holes and neutron stars for the first time, they’ve discovered sizzling hot plasma in the centers of galaxy clusters and in the diffuse space between galax­ies, and they’ve let us make great strides in probing extraordinary black holes that lurk in the centers of all galaxies, ranging from a few million up to a few billion times the mass of the Sun. Their high energy relative to visible light means they’re often created by events of unimaginable violence, phenomena unknown to us fifty years ago (figure 10.1).

The Cosmic Distance Scale

What is the science yield from this premier facility, and how has it changed our view of the universe? In the early years of a space telescope, there’s often a concerted effort to put a lot of time into a few critical projects, so that major results will be obtained even if the telescope fails. There’s understandable tension involved in this decision, since the Hubble has always been oversubscribed by a large factor, and it keeps more astronomers happy if the time is thinly spread among many projects. Riccardo Giacconi, the first director of the Space Telescope Science Institute, was persuaded to set aside substantial time for peer-reviewed “Key Projects.” Early in the history of the facility, three of these were approved. Two of them were successful but are not well known—a medium – deep survey of galaxies,35 and a spectroscopic survey of quasars to probe the hot and diffuse gas in the intergalactic medium36—but the third is rightly considered one of the Hubble Space Telescope’s finest achievements.

As we saw in the chapter on Hipparcos, distance is fundamental to astronomy, yet it’s one of the hardest things to measure. In the everyday world we judge distance based on familiarity with the size of a tree or a person, for example, or the brightness of a lamp or a street light. But in the universe, objects like stars and galax­ies range over many orders of magnitude in size and brightness, so their apparent size or brightness is a very unreliable guide to distance. Is that a bright object far away or a dim object nearby? Is that a large object far away or a small object close by? This type of confusion is common. Considered in a different way, poorly deter­mined distances limit our knowledge of how the universe works. Without knowing how far away an object is, we don’t know its true size or its true brightness. That also means we don’t know its mass or luminosity, which means we can’t have a real physical un­derstanding of something that’s so remote that we’ll never be able to study it in the lab or gather a sample of it. This urge to measure distances accurately becomes acute in the study of the universe as one entity. In an expanding universe, precise distances are needed to answer fundamental questions: what is the size of the universe and how old is it?

Early in the life of the Hubble telescope, hundreds of orbits were devoted to measuring distances to three dozen galaxies. Fittingly, this Key Project used the method that Edwin Hubble had used in the early 1920s to show that the Andromeda nebula was a remote stellar system. Hubble identified examples of a well-known class of variable stars in M31, the Cepheid variables. Cepheids pulsate in a well-understood and well-regulated way, and this behavior mani­fests as a linear relationship between their luminosity and their period of variation.37 By finding Cepheids in a remote galaxy and measuring their periods with a series of images taken over hun­dreds of days, the star’s absolute and apparent brightness can be combined to derive the distance. Cepheids are very luminous and can be seen to large distances. But they’re buried in dense regions of overlapping star images so the sharp imaging of a telescope in space is needed to pick them out. Wendy Freedman, Rob Ken – nicutt, and Jeremy Mould led the project, accompanied by twenty – five other astronomers from around the world.

The Key Project had a goal of measuring the distance scale to an accuracy of 10 percent. This might seem unduly modest, but it’s a reflection of the difficulty of the experiment. In the decade leading up to the launch of Hubble, astronomers had disagreed by 50 percent or more on the distance scale. In particular, the goal was to measure a quantity called the Hubble constant to within 10 percent. The Hubble constant is the current expansion rate of the universe, measured in units of kilometers per second per Megapar­sec. Hubble discovered a linear relation between the distance and the recession velocity of a galaxy. The Hubble constant sets that scaling. So if the Hubble constant is 70, then for every Megaparsec (3.3 million light-years) increase in distance, the recession velocity increases by 70 kilometers per second (157,000 mph). On average, this scaling says that a galaxy a million light-years away is reced­ing from the Milky Way at 47,000 mph, a galaxy 10 million light – years away is receding at 470,000 mph, and so on. Inverting the Hubble constant allows us to project the expansion back to zero separation of all galaxies, and so gives us a good estimate of the age of the universe. By measuring distances out to 20 Megaparsecs (or 66 million light-years), the Key Project would determine the size, expansion rate, and age of the universe.

The formal result of the Key Project was the measurement of a current expansion rate of 73 kilometers per second per Megapar­sec, with a random error of 6 and a systematic error of 8, published in the twenty-eighth paper in the series from team members, which indicates just how productive and prolific one Hubble project can be.38 Synching the distance scale in this way has been a foundation stone in the emergence of “precision cosmology,” where overall attributes of the universe are becoming very well-determined. Al­though the Key Project worked in our cosmic “back yard,” or the local 0.01 percent of the visible universe, it leveraged and helped to improve distance measurements both inward and outward. Hub­ble also was able to measure parallaxes for Cepheids in the Milky Way (along with Hipparcos, which we’ve previously discussed) and tether the distance scale in direct geometric measures. Know­ing Cepheid distances for several dozen galaxies calibrated the use of other types of distance indicators, such as supernovae and the well-defined rotation properties of galaxies, which can be used out into the remote universe.

Grooves in the Cosmic Pond

As early as 1937, James Jeans observed that “the tendency of mod­ern physics is to resolve the whole material universe into waves, and nothing but waves. These waves are of two kinds: bottled-up waves, which we call matter, and unbottled waves, which we call radiation or light.”48 WMAP’s image of the early universe would seem to confirm Jeans’s observation that the universe might be un­derstood in terms of waves. Even as sound waves traveling through the Sun’s plasma reveal information about its structural composi­tion, fluctuations in the plasma that comprised the very early uni­verse reveal critical data about its matter density and structure. Amedeo Balbi, a member of ESA’s Planck mission, the successor to WMAP, writes, “The primordial plasma resonated like an enor­mous bell, and the mechanism which started the vibrations could plausibly only be one: a period of inflation that occurred a tiny fraction of second after the big bang.”49

Balbi points out that galaxies are clustered throughout space and they have a very slight preference for spacings that can be thought of as corresponding to sound waves. These galaxy sepa­rations designate grooves or “acoustic peaks,” as in a wave, and represent gravity and temperature variations on the cosmic micro­wave background, which evolved into a subtle imprint on the dis­tribution of galaxies. One wave that’s clearly detected in the galaxy distribution has a scale of 300 million light-years.50 Astrophysicist Jean-Pierre Luminet likewise claims that the early universe “‘rang’ like a musical instrument.” He explains that the variations or peaks and troughs we see in the cosmic microwave background reveal details of the universe’s mass and density in much the same way acoustic waves reverberating through a drum reveal its struc­tural properties. “If you sprinkle sand on the surface of a drum,” writes Luminet, “and then gently vibrate the drum skin, the grains of sand will assemble into characteristic patterns” that reveal data regarding “the size and shape of the drum” or “the physical nature of the drum skin.”51 Similarly, in analyzing the variation in clusters and superclusters of galaxies, we are gathering details about the matter density of the primeval universe.

University of Virginia astronomer Mark Whittle likewise char­acterizes the variations in the microwave background as similar to the crest and trough of sound waves: “The waves are actually very long; they’re many thousands of light years, and so they cor­respond to frequencies, pitch which is very, very low by human standards, roughly 50 octaves below human ears.”52 Whittle has produced a sound file simulating what the big bang would sound like if modulated for the human ear. Describing his recreation of the acoustic peaks in the cosmic microwave background as a “sort of a raw, deep roaring sound,” Whittle is quick to note that there’s “actually musicality present.”53 He describes WMAP’s image of the microwave background as “a microscope. . . a telescope. . . a time machine, all rolled into one, and stored in it is enough infor­mation to kind of diagnose what the character of the universe is today, what its future will be and what its birth was.” Of this “ex­traordinary document,” Whittle reminds us that embedded in the image is the primeval narrative of the universe “written by nature in nature’s own language.”54 COBE and WMAP (and now Planck) have given nature a voice.

Amedeo Balbi observes in The Music of the Big Bang, “Ripples in the matter density of the early Universe had to leave a perma­nent imprint in the ancient cosmic light—as a seal impressed into wax.”55 Cosmologists theorize that etched into the primordial plasma at the beginning of time were density and heat variations that became the galaxy clusters we observe today. Balbi’s meta­phor of matter density fluctuations imprinted on the cosmic mi­crowave background as indentations in wax brings to mind an early method of creating phonograph records by etching grooves in wax. Early sound recordings involved “engraving” data into a wax overlay of a zinc record. Music or voice data were recorded by tracing with a sharp stylus a spiral onto beeswax coating the zinc record. The disc was then treated with chemicals that pre­served the grooves where the stylus had removed the wax, after which the phonograph record could be played.

As early as 1931, Georges Lemaitre apparently wondered whether information about the universe had been recorded in the primordial quantum, even as information is preserved in the grooves of a phonograph record. Lemaitre observed that “the whole story of the [universe] need not have been written down in the first quantum like the song on the disc of a phonograph.”56 However, the WMAP results suggest that, in fact, it was. From Lemaitre to Balbi, the technology of the grooved record and the shape of an acoustic wave served as apt metaphors for peaks in the cosmic microwave background.57 Had we some other technology for recording sound in the time of Lemaitre, perhaps astronomers would have characterized these acoustic peaks in other terms. On the other hand, scientists find that acoustic and electromagnetic waves are means by which the universe, the stars, and planets tell their story. Astronomers and cosmologists, since Pythagoras, have never given up on finding music in the cosmos. And now they have.

X-rays in Popular Culture

News of Rontgen’s discovery of X-rays rippled around the world. “When Rontgen discovered X-rays in November of 1895 by plac­ing his hand between a Crookes Tube and a florescent screen, the medical applications of the technology were immediately appar – ent.”4 By January 1896, Rontgen had issued a report regarding his experiments to media in Europe and the United States. The public was immediately fascinated by the possibility of seeing through seemingly solid objects or inside the human body, and the topic made headlines in newspapers and weeklies. Apparently, X-r ay

X-rays in Popular Culture

Figure 10.1. At the end of the nineteenth century, X-rays were harnessed for medical imaging, where dense material like bones cast a shadow in X-rays. In the astronomical realm, a very hot gas or plasma emits X-rays, as do regions near compact objects like black holes. The X-rays may also be absorbed by intervening material, and they can only be detected by a satellite above the Earth’s atmosphere (NASA/CXC/M. Weiss).

“mania” swept through the public sphere but at a level far sur­passing a simple cultural fad, explains Nancy Knight, who notes that “X-rays appeared in advertising, songs, and cartoons.”5 John Lienhard similarly reports, “Seldom has anything taken hold of the public imagination so powerfully and completely. . . . Right away, magazine cartoons celebrated the idea. A typical one showed a man using an X-ray viewer to see through a lady’s hat at the theatre.”6

Edwin Gerson has investigated the speed with which X-rays were incorporated into the branding of products in the United States, and he explores why so many marketers used the term X – ray to appeal to consumers. Being a medical doctor, Gerson began collecting household products dating back to the 1890s, none of which have anything whatsoever to do with X-rays. One could purchase Sniteman’s X-Ray Liniment for horses and cattle, and Patt’s X-Ray Liniment for people. X-Ray Golf Balls, ostensibly to improve the accuracy of one’s game, were sold by John Wana – maker of New York. There was the D-cell X-Ray flashlight battery, X-Ray Stove Polish, X-Ray Cream Furniture Polish manufactured in New York, and X-Ray Soap made in Port Huron, Michigan. X-Ray Blue Double Edge razor blades were touted as “the fin­est blade known to science,” while drinking fountains for chicken houses were marketed by the X-Ray Incubator Company in Wayne, Nebraska. Housewives could purchase an X-ray Coffee Grinder or the X-Ray lemon squeezer, and the X-Ray Raisin Seeder was available as early as November 1896. A company from Baltimore, Maryland, sold boxes of X-Ray headache tablets, with 8 pills for ten cents promising relief in just fifteen minutes.7 Clearly, adver­tising by means of non sequitur is not just a phenomenon of the modern age.

The popular fascination with X-rays continued for decades. By 1924, an X-ray shoe fitter was deployed by shoe vendors to image both feet inside a new pair of shoes. David Lapp reports that in the United States “there were approximately 10,000 of these fluo – roscopes in use, being made by companies such as Adrian X-Ray Shoe Fitter,” and that by the early 1950s most shoe stores were using the devices.8 As Gerson points out, “The public was simply astonished with X rays, and advertisers played off this spellbound attention by adding the name to almost any type of product. . . . Not only did the image of the X ray convey a sense of cutting-edge technology, it also functioned as a metaphor for ‘powerful unseen truth and strength.’”9

Researchers and medical personnel working with X-rays were frequently exposed to dangerous or fatal levels of radiation, in­cluding Elizabeth Fleischmann, who at age 28 read a news article on how to build an X-ray device and by 1900 became the best medical radiologist in the United States. But in ten years’ time, Fleischmann had been so badly overexposed to radiation by im­aging her patients and developing the films that she did not sur – vive.10 At the time, the effect of exposure to radiation was poorly understood and this ignorance played out in dangerous exposure for both medical practitioners and those working with the new technology for purposes of entertainment. Nancy Knight, for in­stance, indicates that “papers reported daily” on Thomas Edison’s efforts to X-ray a person’s brain in order to figure out how the brain functions.11

Allen Grove reports that some speculated at the time that the new technology might afford a kind of X-ray vision that might make it possible to capture on film the images of ghosts, appar­ently a popular notion in England. He also comments that within months of Rontgen’s announcement, theaters were headlining performances inspired by the popularity of X-rays.12 Piano sheet music for American composer Harry L. Tyler’s “X Ray Waltzes” from 1896 depicted on its cover a man holding his hand under an X-ray tube. Beneath the man’s hand appears a skeletal X-ray image. In fact, in 2010, Tyler’s waltzes were dusted off and fea­tured in a BBC broadcast titled “Images that Changed the World.” And, any discussion of X-rays in popular culture must recall that in the 1930s, when writer Jerry Siegel and artist Joe Shuster in­vented the prototypical superhero, it was inevitable that Superman would be gifted with X-ray vision. Though Superman didn’t have such ability at the outset, in later adventures he is able to see in multiple wavelengths of the electromagnetic spectrum, including radio waves, infrared, ultraviolet, and eventually X-rays.13

Rontgen’s discovery had a deep shaping effect on the arts. This was because X-rays were an entree into a hidden world, the “world within the world” represented by the interior structure of atoms and molecules. In 1912, less than twenty years after the initial dis­covery, physicist Max von Laue showed that X-rays were a form of electromagnetic radiation because they diffracted when inter­acting with matter. A year later, the father and son team of William Henry and William Lawrence Bragg described mathematically how X-rays scattered within a crystal, winning the Nobel Prize in Physics for their work in 1915. This opened the door to X-ray crystallography, a powerful tool for measuring the spacing and arrangement of atoms within a solid. The impact of this discovery was particularly strong in the visual arts, which were undergoing their own revolution with the onset of Fauvism, Cubism, and Fu­turism. The X-ray was liberating because to artists it “proved that the external is not valid, it’s just a false layer.”14

Art historian Linda Dalrymple Henderson contends that X-rays suggested the possibility of stepping into the fourth dimension. She writes, “From the 1880’s to the 1920’s, popular fascination with an invisible, higher dimension of space—of which our famil­iar world might be only a section or shadow—is readily apparent in the vast number of articles and the books. . . published on the topic.” Henderson has demonstrated that modern artists read­ily embraced X-rays, and their ability to expose realities and per­spectives not perceptible to the human eye, as suggestive of four­dimensional space.15 Cubist paintings, with their simultaneous depiction of all sides of a seemingly transparent object, and their suggestion of interior planes, explains Henderson, “are testaments to the new paradigm of reality ushered in by the discovery of X – rays and interest in the fourth dimension. Such paintings are new kinds of ‘windows’—in this case, into the complex, invisible reality or higher dimensional world as imagined by the artist.”16 The in­spiration was sometimes very direct. According to historian Arthur Miller, “Picasso’s Standing Female Nude” (1910) was inspired by the power of X-rays to glimpse beyond the visible: what you see is not what you get. In this case, the inspiration was X-ray photo­graphs taken to diagnose the illness of Picasso’s mistress, Fernande Olivier. Superposed on a background of planes, her body lies open to reveal pelvic hip bones made up of geometrical shapes: forms reduced to geometry—the aesthetic of Cubism, inspired by mod­ern science.”17 From the arts, to medicine, and particularly through astronomy and space exploration, X-rays have profoundly altered human culture.

Dark Force

The Hubble Space Telescope has touched every area of astronomy. But some of its key contributions have profoundly shaped our view of the universe. One of the original hopes for the Hubble was to extend the Key Project, which measured the local or current ex­pansion rate, and measure the entire expansion history of the uni­verse over cosmic time. Hubble’s sensitivity and resolution allow it to observe supernovae in distant galaxies. A Type 1a supernova is a white dwarf star that detonates as a result of mass steadily siphoned onto it from a massive companion star. When the white dwarf exceeds the Chandrasekhar limit, which we encountered in the last chapter, it collapses and then explodes as a supernova. This well-regulated process means it’s a “standard bomb” with an in­trinsic brightness that doesn’t vary from one supernova to another by more than 15 percent. At peak brightness, the supernova rivals its parent galaxy in brightness (figure 11.4), so these explosions can be seen to distances of 10 billion light-years or more.39

In the mid-1990s, two groups studying supernovae saw some­thing utterly unexpected.40 In an expanding universe, the effect of normal matter and dark matter is to slow down the expansion rate. By looking back in time with more and more distant super­novae, these researchers had expected to see supernovae appear­ing slightly brighter than expected for a constant expansion rate. The reasoning is that deceleration reduces the distance between

Dark Force

Figure 11.4. Although the Hubble Space Telescope is relatively small by modern standards, its sharp imaging and sensitive instruments allow it to see supernovas at distances of billions of light-years. When they die, these stars rival the bright­ness of their surrounding galaxies, enabling the distances to those galaxies to be measured (NASA/STScI/P. Garnavich).

us and a supernova relative to constant expansion, making it ap­pear brighter. Instead, they saw the opposite effect: the distant su­pernovae were dimmer than expected. The interpretation was the distance to the dying star was larger than expected. Rather than decelerating, the universe has been accelerating! Cosmic accelera­tion is a very puzzling effect, because it implies a force acting in op­position to gravity. No such force is known in physics, so the cause of the phenomenon was called “dark energy,” where that phrase is really just a placeholder for ignorance. Dark energy seems to have the character of the cosmological constant, the term that Ein­stein added to the solutions of his equations of general relativity to suppress natural expansion (and which he later called the greatest blunder of his life). It’s new and fundamental physics.

The discovery of cosmic acceleration was based on images and spectra taken with ground-based telescopes. The Hubble Space Telescope didn’t make the initial discovery. But confirming the re­sult, extending the measurements to higher redshift, and putting constraints on the nature of dark energy—all of those have been essential contributions. Hubble’s depth has been used to trace the expansion history back over two thirds of the age of the universe. The data show that acceleration reverts to deceleration more than 5 billion years ago.41 Astronomers can now apportion the two major components of the universe: dark matter and dark energy. Dark energy accounts for 68 percent, dark matter accounts for 27 percent, diffuse and hot gas in intergalactic space is about 4.5 percent, and all the stars in all of the galaxies in the observable uni­verse amount to only 0.4 percent of the cosmic “pie.” Dark forces govern the universe.

Imagine the expanding universe with a brake and an accelerator. The “driver” isn’t very competent so they press both pedals at the same time. Dark matter is the brake because gravity slows the ex­pansion. Dark energy is the accelerator. In the first two thirds of the expansion history, the dark matter dominates and the expansion slows with time. But the effect of dark matter weakens, because the density and the gravity force go down, while dark energy has a constant strength in both time and space. So the pressure on the brake eases while the accelerator is pressed the same amount, and about 5 billion years ago all galaxies started to separate at ever – increasing rates. Some cosmologists consider it an unexplained coincidence that dark energy and dark matter—two mysterious entities with fundamentally different behavior—happen to have roughly the same strength and crossed paths relatively recently in cosmic time. This is the only time in cosmic history they are close to equal strength; for most of the early history of the universe, dark matter was utterly dominant and forever into the future dark energy will dominate. This coincidence only sharpens the enigma.

Precision Cosmology

WMAP has not only put us “in tune” with the cosmos; it has re­fined and sharpened our view of the extraordinary event that cre­ated all matter and energy 13.8 billion years ago.

WMAP has taken quantities that were poorly known or only hinted at and turned them into well-measured cosmological param – eters.58 The temperature is measured to a precision of a thousandth of a degree. Since space can be curved according to general relativ­ity, the universe can act as a gigantic lens. To do this vast optics experiment we look at the microwaves that have been traveling across space for billions of years. The fundamental harmonic of the microwave radiation sets the size of the “spot.” Radiation from that typical spot size travels through space and the angular size can be magnified or de-magnified depending on whether space has positive or negative curvature, which is like the universe acting as either a convex or a concave lens. WMAP has shown that the spot size doesn’t change so the universe is behaving like a smooth sheet of glass. The inference is that space is not curved; the universe is flat to a precision of 1 percent.59 This is just as expected from inflation.

WMAP has measured the mass and energy of the universe with unprecedented precision. The ratio of fundamental to first harmonic powers depends on the baryonic or normal matter con­tent of the universe. Ordinary atoms only make up 4.6 percent of the universe, to within 0.1 percent. The strength of the second harmonic is sensitive to dark matter, and shows that dark matter is 23 percent of the universe, to within 1 percent.60 Knowing the mass and energy content of the universe, General Relativity can be used to calculate the current age. It’s 13.73 billion years with a precision of 1 percent or 120 million years, though that precision depends on assuming that space is exactly flat (which is a good assumption). These numbers have been refined and slightly altered by Planck. The cosmic “pie” has dark slices and just a sliver of vis­ible stuff (figure 12.4).

We’ve also been able to learn about the epoch when the first stars and galaxies formed using the WMAP data. If stars formed soon enough after recombination, they would have ionized the still-diffusing gas. That would have recreated the conditions where photons bounce off electrons, as was routinely the case before re­combination. This late scattering imprints polarization on the mi­crowave radiation, analogous to sunlight being polarized when it bounces off a water surface. Polarization requires a special direc­tion, and that can only be seen if photons travel relatively freely before interacting. Before recombination no polarization is ex­pected. WMAP saw a polarization indicating that 20 percent of the photons were scattered by a sparse fog of ionized gas a couple of hundred million years after the big bang. This is surprising because astronomers didn’t expect the first stars to form that quickly.61

The sum of all WMAP’s improvements leaves little doubt that the universe began with a hot big bang. The model is described quite precisely and any competing idea would have to clear some very high bars of evidence to be viable. It’s extraordinary that we can know some attributes of the overall universe better than we know attributes of the Earth.

Precision Cosmology

Figure 12.4. Observations of the microwave background radiation combined with ground-based observations determine the contents of the universe. Most of the universe is in the form of enigmatic dark matter and dark energy, with just a small component of the normal matter that comprises all stars, planets, and people (NASA/WMAP Science Team).

A Gentle Astrophysical Giant

In 1923, Wilhelm Rontgen died as one of the most celebrated physicists of his time. A modest man, he had declined to take out a patent on his discovery, wanting X-rays to be used for the benefit of humankind. He also refused to name them after himself and donated the money he won from his Nobel Prize to his university.

That same year Subrahmanyan Chandrasekhar started high school in a small town in southern India. Chandra, as he was universally known, would grow into another great but modest scientific fig­ure. Chandra means Moon or luminous in Sanskrit. He was one of nine children and although his family had modest means, they valued education; therefore he was home schooled since local pub­lic schools were inferior and his parents couldn’t afford a private school. His family hoped Chandra would follow his father into government service but he was inspired by science and his mother supported his goal. In addition, he had a notable role model in his uncle, C. U. Raman, who went on to win the Nobel Prize in Physics in 1930 for the discovery of resonant scattering of light by molecules.18

Chandra’s family moved to Madras and he started at the univer­sity there, but was offered a scholarship to study at the University of Cambridge in England, which he accepted. He would never live in India again. At Cambridge he studied, and held his own, with some of the great scholars of the day. As a young man he fell into a controversy with Arthur Eddington, at the time the foremost stellar theorist in the world, which upset him greatly. Eddington refused to accept Chandra’s calculations on how a star might con­tinue to collapse when it had no nuclear reactions to keep it puffed up. Chandra was a gentle man, unfailingly polite and courteous. In part due to this conflict, he chose to accept a position at the Uni­versity of Chicago, where he spent the bulk of his career.

His name is associated with the Chandrasekhar limit, the theo­retical upper bound on the mass of a white dwarf star, or about 1.4 times the Sun’s mass. Above this limit, the force of gravity over­comes all resistance due to inter-particle forces, and a stellar corpse will collapse into an extraordinary dark object, either a neutron star, or if there’s enough mass, a black hole. In the 1970s, he spent several years developing the detailed theory of black holes. Chan­dra was amazingly productive and diverse in his scientific interests. He wrote more than four hundred research papers, and ten books, each on a different topic in astrophysics. For nineteen years, he was the editor-in-chief of The Astrophysical Journal, guiding it from a modest local publication to the international flagship jour­nal in astronomy. He mentored more than fifty graduate students while at the University of Chicago, many of whom went on to be the leaders in their fields. In 1983, he was honored with the Nobel Prize in Physics for his work on the theory of stellar structure and evolution.

Through his long career, Chandra watched the infant field of X-ray astronomy mature. The telescopes flown in sounding rock­ets in the early 1960s were no bigger than Galileo’s spyglass. Just before its 1999 launch, NASA’s Advanced X-Ray Astrophysical Facility was renamed the Chandra X-ray Observatory (CXO) in honor of this giant of twentieth-century astrophysics.19 In a span of less than four decades, Chandra improved on the sensitivity of the early sounding rockets by a factor of 100 million.20 The same sensitivity gain for optical telescopes, from Galileo’s best device to the Hubble Space Telescope, took four hundred years—ten times longer!