The Day We Found the Universe - Marcia Bartusiak [31]
Then, on the evening of August 29, 1864, he shifted his attention from stars to nebulae. He aimed his telescope at a bright planetary nebula in the Draco constellation. He recalled in a memoir years later that he felt “excited suspense, mingled with a degree of awe” as he put his eye to the spectroscope. The spectrum he beheld was a surprise: “A single bright line only!” he noted. “At first I suspected some displacement of the prism, and that I was looking at a reflection of the illuminated slit… This thought was scarcely more than momentary; then the true interpretation flashed upon me… The riddle of the nebulae was solved. The answer, which had come to us in the light itself, read: Not an aggregation of stars, but a luminous gas.” A star was simply too complex to be emitting a single spectral line; the emitter had to be a gaseous cloud, he thought, readying itself for stellar construction. In light of this and other findings, it became more popular to think of all nebulae as embryonic stars and planetary systems in the making. This idea was strengthened in 1888 when the English celestial photographer Isaac Roberts captured a full picture of the Andromeda nebula, an astounding feat at the time because of its faintness. When it was displayed at a Royal Astronomical Society meeting, murmurs could be heard in the audience: “The nebular hypothesis made visible!” The photo displayed a bright core surrounded by a wide, hazy cloud. When Huggins saw the image, he exclaimed that it had to be “a planetary system at a somewhat advanced stage of evolution; already several planets have been thrown off.”
With the great weight of his opinion, Huggins helped force the pendulum the other way. The island-universe theory was no longer a viable contender; it became passé. In his late-nineteenth-century A Text-book of General Astronomy for Colleges and Scientific Schools, a classic in its day, astronomer Charles Young stressed that astronomers no longer considered a spiral nebula as “a ‘universe of stars,’ like our own ‘galactic cluster’ to which the sun belongs…. In some respects this old belief strikes one as grander than the truth even. It made our vision penetrate more deeply into space than we now dare think it can.” To Young, the Milky Way was some 10,000 to 20,000 light-years wide. “What is beyond the stellar system, whether the star-filled space extends indefinitely or not, no certain answer can be given,” he said.
The island-universe theory had already been shaken in 1885 when a nova—a new pinpoint of orange-yellow light—was sighted near the center of the Andromeda nebula. At its brightest, around the sixth magnitude, this nova was nearly as luminous as the entire nebula. “This strange and beautiful object has broken silence at last, though its utterance may be difficult to interpret,” said the Greenwich Observatory astronomer E. Walter Maunder.
If Andromeda were a distant external universe, it was reasoned, the nova had to be shining with the energy of some fifty million suns, “a scale of magnitude such as the imagination recoils from contemplating,” said Agnes Clerke, a nineteenth-century historian of astronomy. That was actually a stupendous underestimate of the nova's power, but even that tally was too preposterous to consider in any serious fashion in 1885. The idea that a star could totally obliterate itself as an explosive supernova was not even a fantasy at the time. There was no physics to explain it. Stars were regarded as stable and enduring. It seemed more likely that the nova was an infant sun condensing and turning on within a vast collection