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Hubble Spots Tiny Seed Galaxies

Sept. 10, 2007 — Astronomers using a pair of space telescopes have found nine tiny start-up galaxies 100 to 1,000 times smaller than the Milky Way.

The structures formed when the universe was about one billion years old, just a fraction of its present age of 13.7 billion years.

The galaxies are packed with hot, young blue stars burning only helium and hydrogen, byproducts from the Big Bang explosion that created the universe. Older stars recycle heavier elements fused in earlier generations of stars.

"You need a first generation of stars to make dust," said Ray Villard, with the Space Telescope Science Institute in Baltimore, Md.

Working from the landmark ultra-deep field image made by the Hubble Space Telescope, James Rhoads of Arizona State University in Tempe and Chun Xu of the Shanghai Institute of Technical Physics in China were the first to spot the galaxies, which radiate brightly with glowing hydrogen.

Scientists then used the infrared-sensitive Spitzer Space Telescope to check for cooler emissions that would be associated with dust surrounding older stars. Finding none, astronomers realized they were looking at original structures formed after the Big Bang.

"It is the absence of infrared light that was conclusive in showing that these are truly young galaxies without an earlier generation of stars," said Sangeeta Malhotra, also of Arizona State.

Astronomers believe small galaxies were the building blocks for the mammoth structures we see today, but they did not imagine galaxies so tiny.

"These are among the lowest mass galaxies ever directly observed in the early universe," said Nor Pirzkal of the Space Telescope Science Institute in Baltimore, Md.

The mini-galaxies are similar to Lego building blocks that piece themselves together to form larger and more complex structures, Villard said.

"Everything with Hubble keeps pushing the formative years of the universe farther and farther back," he said. "When we look, we should be able to find the precursors to these galaxies."

That follow-up work will fall to Hubble's replacement, the James Webb Space Telescope, which is scheduled for launch in 2013.

"Hubble is the first frontiersman to take us into this undiscovered country one billion years after the Big Bang," Villard added. "We're getting all these tantalizing clues as to what happened at this epoch."