Massive "Big Baby" Galaxy Found in Distant Quadrant of Space

Brian Handwerk
for National Geographic News
September 28, 2005
New images reveal a "big baby" galaxy that may lie as far from the Earth as any galaxy yet discovered. Astronomers say the new galaxy is surprisingly massive and mature for its early age—raising questions about how galaxies are formed.

"This is truly a significant object," said Richard Ellis, an astronomer at the California Institute of Technology (Caltech) in Pasadena and a member of the discovery team.

"Although we are looking back to when the universe was only 6 percent of its present age, this galaxy has already built up a mass in stars eight times that of the Milky Way."

The galaxy represents a time when the universe was just 800 million years old. Scientists place the universe's age at around 14 billion years.

The potential evidence for early star birth may shake commonly held theories of galaxy formation.

"It's telling us that star formation and the processes that led to the collapse of galaxies probably occurred at much earlier times than we thought," Ellis said.

The Birth of Galaxies

The universe's other young galaxies are generally much smaller. Scientists believe that many of these smaller galaxies gradually combined over time to build larger galaxies like the Milky Way.

But the new galaxy not only contains hundreds of billions of stars, it seems to have finished its star formation at a tender age.

"This galaxy, named HUDF-JD2, appears to have bulked up quickly, within the first few hundred million years after the big bang," said Bahram Mobasher of the Space Telescope Science Institute in Baltimore.

"It made about eight times more mass in stars than are found in our own Milky Way, and then, just as suddenly, it stopped forming new stars," he said.

No one can be sure how typical or atypical the massive young galaxy's formation might be.

"Of course there is a range," said Mark Dickinson of the National Optical Astronomy Observatory in Tucson, Arizona. "Some galaxies would have formed more quickly, and it might just be that we're seeing an extreme example of that."

But, Dickinson continued, "it's a sample of one. You can ask [in light of current theories] how likely is it that you'd find a galaxy like this? The answer is that it's not very likely, not that it couldn't exist."

At the Edge of Observation

The HUDF-JD2 galaxy is located in a tiny patch of sky called the Hubble Ultra Deep Field.

No one knows for sure how far away the galaxy lies because the discovery is pushing the very limits of telescope technology.

"It's definitely a galaxy, it's definitely very distant, there's no question about that," Dickinson said. "Is it at the very edge of the observable universe, or not quite that far?"

Hubble cannot see the galaxy in visible light, but this non-observation may hold important information.

"The fact that we don't see it in the deepest optical images ever taken is one of the reasons we believe it's as old as it is," Dickinson explained.

As the universe expands, light is stretched and shifted to longer, redder wavelengths. The newfound galaxy's visual wavelengths appear to have been so reduced that they were absorbed by space hydrogen as they traveled the billions of light years toward Earth.

The galaxy was spotted via Hubble's infrared images and by an infrared camera on the Very Large Telescope at the European Southern Observatory.

Such state-of-the-art equipment enabled astronomers to discover the galaxy, but the big baby's exact distance will likely remain a mystery until the next generation of telescopes emerges.

"We're at the frontiers of what we can do with our existing telescopes," Caltech's Ellis explained.

Ellis spoke from an Aspen, Colorado, meeting where Caltech is collaborating with other institutions on the construction of a 98-foot (30-meter) telescope.

The instrument would have ten times the power of the world's largest telescope—the 33-foot (10-meter) instrument at the W.M. Keck Observatory atop Hawaii's Mauna Kea volcano.

The discovery of the new galaxy provided another compelling reason to develop telescopes that can peer further back into the universe's distant past.

"It's like crossing the ocean and meeting a lone seagull, a forerunner of land ahead," Ellis said. "There is now every reason to search beyond this object for the cosmic dawn when the first such systems switched on."

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