01 November 2010

Capturing Primordial Starlight

Edwin Hubble at 100-Inch
 By 1936, Edwin Hubble was a dozen years into his search for distant galaxies. At that time, he could see out to several hundreds of millions of light-years, using the great 100-inch telescope atop California’s Mount Wilson. But even then the smudges on his photographic plates were dim, fuzzy, and next to impossible to identify.

“There,” wrote Hubble in his classic book The Realm of the Nebulae, “we measure shadows and…search among ghostly errors of measurement for landmarks that are scarcely substantial.”

Ever since, astronomers have struggled to trace the evolution of galaxies back through space-time—not just hundreds of millions of light-years but billions. For decades, all that astronomers could say with surety were that distant galaxies and clusters looked a bit “bluer,” a sign of heightened star formation as hoards of young, massive stars, flush with energy, put out more blue light.

Quasars, the brilliant cores of newborn galaxies, had long been sighted at great distances, but astronomers questioned whether they could truly understand the early universe by studying only its most active members.

But thanks to key technological breakthroughs over the last two decades—among them, the Hubble Space Telescope, the opening of giant telescopes in Hawaii and South America, and advances in telescopic detectors—more typical primordial galaxies are now being found, and at greater and greater distances.

UDFy-38135539 (circled in red) lurks within the Ultra Deep Field

The current record holder was recently discovered by a European team of astronomers using the European Southern Observatory’s Very Large Telescope (VLT) in Chile. It’s but a speck in the image, but a sensitive spectrograph allowed the observers to peg its distance. It’s more than 13 billion light-years from Earth and has been christened UDFy-38135539. That’s a mouthful for us but helpful to astronomers: the UDF stands for Ultra Deep Field (a region located in the southern-hemisphere constellation Fornax that was first closely imaged by the Hubble Telescope) and the number pegs its precise position on the sky.

The photons from this distant object started their journey when the universe was only 600 million years old. This was a time when a great fog of hydrogen gas, in which the universe was bathed, was just beginning to break up—cleared out by the fierce ultraviolet light emitted by newborn galaxies. The VLT likely sighted the new record holder through a break in the clouds, a lucky event for the astronomers and for us.  Through this fortuitous window, we get to see a bit of primordial starlight.

Picture Credits: (top) Huntington Library; (bottom) European Southern Observatory

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