There may be two trillion other galaxies


Brian Gallagher writes: In 1939, the year Edwin Hubble won the Benjamin Franklin award for his studies of “extra-galactic nebulae,” he paid a visit to an ailing friend. Depressed and interred at Las Encinas Hospital, a mental health facility, the friend, an actor and playwright named John Emerson, asked Hubble what — spiritually, cosmically — he believed in. In Edwin Hubble: Mariner of the Nebulae, Gale E. Christianson writes that Hubble, a Christian-turned-agnostic, “pulled no punches” in his reply. “The whole thing is so much bigger than I am,” he told Emerson, “and I can’t understand it, so I just trust myself to it, and forget about it.”

Even though he was moved by a sense of the universe’s immensity, it’s arresting to recall how small Hubble thought the cosmos was at the time. “The picture suggested by the reconnaissance,” he wrote in his 1937 book, The Observational Approach to Cosmology, “is a sphere, centred on the observer, about 1,000 million light-years in diameter, throughout which are scattered about 100 million nebulae,” or galaxies. “A suitable model,” he went on, “would be furnished by tennis balls, 50 feet apart, scattered through a sphere 5 miles in diameter.” From the instrument later named after him, the Hubble Space Telescope, launched in 1990, we learned from a series of pictures taken, starting five years later, just how unsuitable that model was.

The first is called the Hubble Deep Field, arguably “the most important image ever taken” according to this YouTube video. (I recommend watching it.) The Hubble gazed, for ten days, at an apparently empty spot in the sky, one about the size of a pinhead held up at arm’s length — a fragment one 24-millionth of the whole sky. The resulting picture had 3,000 objects, almost all of them galaxies in various stages of development, and many of them as far away as 12 billion light-years. Robert Williams, the former director of the Space Telescope Science Institute, wrote in the New York Times, “The image is really a core sample of the universe.” Next came the Ultra Deep Field, in 2003 (after a three-month exposure with a new camera, the Hubble image came back with 10,000 galaxies), then the eXtreme Deep Field, in 2012, a refined version of the Ultra that reveals galaxies that formed just 450 million years after the Big Bang. [Continue reading…]

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