The Day We Found the Universe (9 page)

Gradually found in greater numbers, these celestial objects took on even more importance in 1781 when the celebrated comet hunter Charles Messier published in France his list of more than one hundred nebulae, a directory that is still used today. The Andromeda nebula, for example, is commonly known as M31 because it's the thirty-first nebula in Messier's catalog. Messier, though interested in the nebulae themselves, primarily wanted to let his fellow observers know that these celestial regulars, the most prominent of their kind, should not be mistaken for comets. He was putting up cosmic road signs for his colleagues, pointing out those nebulae visible above the horizon from the latitude of Paris.

No one was more excited by Messier's list than William Herschel, England's soon-to-be crown prince of astronomy. As soon as Herschel received a copy of Messier's catalog, he immediately aimed a telescope at the celestial clouds. “I…saw, with the greatest pleasure, that most of the nebulae, which I had an opportunity of examining in proper situations, yielded to the force of my light and power, and were resolved into stars,” he wrote a few years later. He was the first to make this discovery, using a telescope twenty feet in length with a mirror then twelve inches wide. It was the most powerful in its day, allowing him to see that many of the nebulae (what we now call open clusters and globular clusters) were actually comprised of hundreds and thousands of stars. This led him to the belief that
all
nebulae were far-off systems of stars. Any nebula still appearing cloudlike through his eyepiece, he figured, was simply too distant to behold individual stars clearly.

Herschel promptly initiated a grand hunt for nebulae, literally sweeping the heavens with his giant reflector. Previous endeavors to spot nebulae paled beside this effort. By 1786 he had sighted a thousand new nebulae and star clusters; three years later he added hundreds more. “These curious objects, not only on account of their number, but also in consideration of their great consequence, [are] no less than whole sidereal systems,” he wrote. He even boasted at one point that he had discovered fifteen hundred new universes. Each, he excitedly reported, “may well outvie our milky-way in grandeur.”

Herschel had come late to this pursuit. Raised in the Duchy of Hanover (now part of Germany) within a family of musicians, he fled as a teenager to England, Hanover's ally, in the midst of war. There he supported himself by copying musical manuscripts, composing, giving private lessons, and performing in local concerts. Eventually he obtained financial security by becoming a choral director in the city of Bath. Yet he was restless for more intellectual stimulation.

Inspiration arrived on May 10, 1773. On that day Herschel, then thirty-four years old, bought a copy of a popular astronomy textbook. “When I read of the many charming discoveries that had been made by means of the telescope,” said Herschel, “I was so delighted with the subject that I wished to see the heavens and Planets with my own eyes thro' one of those instruments.” By the autumn he was beginning to handcraft metal mirrors for a reflecting telescope. He became obsessed with his new hobby, soon shifting his interests from the music of the Earth to the music of the heavens. So passionate was his commitment to astronomy that his younger sister, Caroline, who had earlier joined him in England, fed him morsels of food by hand, so that he would not have to pause while grinding and polishing. Pointing his home-built instruments toward the sky, he came to memorize the heavens and in 1781 climactically spotted Uranus, the first planet discovered since the dawn of history. He was promptly elected a fellow of the Royal Society and procured an annual stipend from England's King George III, a pension that at last allowed Herschel to devote himself to his astronomical interests, especially building ever-larger telescopes (the largest he ever constructed was forty feet long).

Herschel was far ahead of his time, as he used his telescope to examine the universe much the way an astronomer would today. While other astronomers in his day focused solely on the motions of the stars and planets, he was determined to discern nothing less than the “construction of the heavens,” the title of one of his most notable papers. He wanted to reach out into distant space, far beyond the realm most studied by his contemporaries. Wright and Kant had done the same, but they were merely theoretical speculators, not practicing astronomers. Herschel insisted that his ideas be “confirmed and established by a series of observations.” Photography was still decades away, so to do this he had to spend hours at his eyepiece, awkwardly perched on a platform at the top of his telescope. So skilled did he become at fashioning telescopes that his instruments were the only ones at the time capable of seeing out to cosmological distances. His tireless assistant Caroline was often with him, jotting down the positions and descriptions of the many nebulae he came upon during his scans of the heavens.

Drawings of nebulae by astronomer William Herschel, 1811
(From
Philosophical Transactions of the Royal Society of London
101 [1811]: 269-336, Plate IV)

“I have seen double and treble nebulae, variously arranged; large ones with small, seeming attendants; narrow but much extended, lucid nebulae or bright dashes; some of the shape of a fan, resembling an electric brush, issuing from a lucid point, others of cometic shape, with a seeming nucleus in the center;…when I came to one nebula, I generally found several more in the neighbourhood,” he reported. At one point, Herschel even imagined other beings residing within those nebulae, looking back at us: “The inhabitants of the planets that attend the stars which compose them must likewise perceive the same phænomena. For which reason they may also be called milky-ways by way of distinction.” He seemed to be confirming the Wrightian and Kantian visions: that the universe is vastly larger and more complex than previously imagined. The Milky Way was a cohesive system of stars and beyond that was a limitless universe, populated by other stellar systems, comparable to our own.

Astronomers might have become quite comfortable with and accepting of the idea that other galaxies existed, more than a century before Hubble proved it conclusively, if not for the fact that Herschel abruptly changed his mind about those hundreds of “new universes.” A new observation forced him to reconsider his previous assertions. It happened on a cold November evening in 1790 when Herschel came upon an eighth-magnitude star that was surrounded by a faintly luminous atmosphere of considerable extent. “A most singular phænomenon!” he jotted down in his notebook. He called this haze a “planetary nebula” because of its resemblance to a planetary disk (as noted earlier, now known to be an aging star shedding its outer envelope of gas). “Cast your eye on this cloudy star,” he wrote, “and the result will be no less decisive…that
the nebulosity about the star is not of a starry nature…
Perhaps it has been too hastily surmised that all milky nebulosity, of which there is so much in the heavens, is owing to starlight only.” In Herschel's mind, nebulae had to be comprised of either stars or a “shining fluid”—not both. So he decided that any nebulae that remained unresolved through his telescope were no longer distant stellar systems, but instead collections of luminous matter, likely the stuff out of which stars ultimately condensed.

Herschel's telescopes were so much better than the equipment of any other astronomer at the time that his colleagues trusted his judgment on this matter. They simply didn't have the telescopic power to confirm his findings. As a result, Herschel's pronouncement became the accepted wisdom. The universe swiftly shrank back to the borders of the Milky Way. We were alone in the universe once again … at least for a while.

Throughout the nineteenth century, the two explanations for the unresolved nebulae went through a relentless tug-of-war, one side winning the hearts of astronomers for a time, then the other. Some insisted they were nearby clouds of gas, while others championed them as far-off islands of stars. Each faction was seeking a solitary explanation, simple and elegant—and that meant choosing between the two possible options.

Cosmology at this time continued to be of more interest to independent astronomers than the professionals who toiled at university-or government-sponsored observatories, and it was one of these self-directed observers who gave renewed hope to those who favored the idea that the dim nebulae were similar to the Milky Way, separate galaxies whose individual stars over the vast distances melted into a uniform pool of light. The excitement arose when William Parsons, the third Earl of Rosse, constructed a giant telescope on the grounds of his ancestral home, Birr Castle, in central Ireland, seventy miles west of Dublin. So big was the telescope tube that at the observatory's opening ceremony, a dean of the Church of Ireland walked right down the huge cylinder wearing a top hat and an open umbrella.

Young Rosse (then Lord Oxmantown, prior to succeeding his father in the earldom) served in the British Parliament, but his passion was telescope-building, with his decided aim, according to those who knew him, “to make a telescope of the largest dimensions possible with the resources of his time.” In 1834, at the age of thirty-four, Rosse left politics to devote himself to a newfound career as a gentleman scientist. He had long wanted to surpass Herschel's instruments in size and devised the methods himself for casting and polishing the metal mirror in his own workshops, personally training the laborers on his estate to assist him. Though an aristocrat, he put on no airs; a British reporter once caught him working at a vise, his shirtsleeves rolled up, displaying brawny arms. The mirrors he constructed were made out of a tin and copper alloy, a blend that resulted in a reflectivity almost as high as silver. Rosse's first big success was a three-foot-wide mirror mounted in a tube twenty-six feet long. “It is scarcely possible to preserve the necessary sobriety of language in speaking of the moon's appearance with this instrument,” reported a friend.

The triumph gave Rosse the confidence to construct a mirror twice the size, taking no notice that the Irish weather was more infamous for rain than clear skies. First put into operation in 1845, this reflector, when erect, was said to resemble one of the ancient round towers of Ireland and was dubbed the “Leviathan of Parsontown.” “Sweeping down from the moat towards the lake, stand two noble masonery walls,” reported a houseguest. “They are turreted and clad with ivy, and considerably loftier than any ordinary house. As the visitor approaches, he will see between those walls what may at first sight appear to him to be the funnel of a steamer lying down horizontally.” It was the telescope's immense wooden tube, which was more than fifty feet long and held a polished metal mirror six feet in diameter. This mirror provided fourteen times more surface area for collecting light than Herschel's most productive telescope. A pulley system, attached to the top of the tube, allowed the telescope to be pointed by two men on the ground. A series of staircases and galleries provided the observer access to the mouth of the great tube. It was an astounding telescope size for its time and wouldn't be matched for another seven decades.

The Leviathan's prime targets were the “strange stellar cloudlets that fleck the dark vault of the heavens.” Rosse was determined to see if he could resolve the nebulae—those that remained stubbornly cloudlike—into stars. But what he turned up was something even more intriguing.

In the spring of 1845, Rosse and his assistant Johnstone Stoney began to study the fifty-first nebula, M51, in Messier's famous catalog. When William Herschel viewed it years earlier, he saw only a bright round nebula; his son later observed it as a ring with two branches. But Rosse, to his amazement, detected a distinct coiling, arms of gas wrapped around M51's center like a whirling pinwheel. No one had ever anticipated something like this. Some nebulae were shaped like spirals, “a structure and arrangement more wonderful and inexplicable than anything which had hitherto been known to exist,” reported Great Britain's Royal Astronomical Society.

In these days before astrophotography, Rosse sketched a picture of the configuration with painstaking care. “With each successive increase of optical power, the structure has become more complicated and more unlike anything which we could picture to ourselves,” Rosse reported. “That such a system should exist, without internal movement, seems to be in the highest degree improbable.” This is when M51 came to be called the Whirlpool because of the striking swirl of its appearance. Rosse went on to discern more than a dozen such spiral nebulae in the celestial sky.