Hot, Young Stars Shed Light On How Galaxies Form

Astronomers using the Hubble Space Telescope have opened a window on what may be a nursery for the formation of galaxies in the early universe. In the process, they are helping to shed some light on how galaxies are created.

Using the orbiting observatory, the team has discovered a tightly packed set of clumps containing hot, young stars roughly 11 billion light-years from Earth. Their size, distance, spacing, and the apparent merger of four of the objects strongly suggest that galaxy cores are being formed.

"We've never seen so many of these objects in a single exposure and so small," says Sam Pascarelle, a graduate student at Arizona State University, who wrote up the results being published in this week's issue of the journal Nature. "We are convinced that these objects are ... part of the general formation process of galaxies in the early universe." The results were announced yesterday at a press briefing at NASA headquarters in Washington.

Astronomers studying the evolution of stars have long been able to view regions of the sky where clouds of hydrogen gas collapse and form new stars. The new effort with the Hubble could open a similar view for astronomers studying the evolution of the universe following the Big Bang, the explosion that cosmologists theorize gave rise to the universe some 15 billion years ago.

In particular, scientists have been trying to understand how the matter in the universe could condense into the structures we see - from stars and galaxies to vast groupings of galaxies separated by vast voids. In the early stages following the Big Bang, the universe's inventory of matter was much more evenly distributed. Observations like those of Mr. Pascarelle and his colleagues can be used to test various theories about how the universe evolved.

Serendipity played a key role in the discovery, says University of Alabama astronomer William Keel, who also is part of the collaboration. The team was using a ground-based telescope to gather data on a galaxy about 11 billion light-years away. In the process, they discovered several of the faint blue nurseries in the field around the galaxy. After confirming their finding with another telescope, they used Hubble to take a clearer look.

What they found were 18 objects, each containing about a billion stars and measuring 2,000 light-years across. By contrast, the Milky Way is roughly 100,000 light-years across. But at its thickest point, it is only 8,000 light-years across.

Through repeated merging, Dr. Keel says, the clumps "will grow big enough to become the bulges" of elliptical or spiral galaxies.

The team, which also includes Arizona State astronomers Roger Windhorst and Stephen Odewahn, notes that ground-based surveys of galaxies have revealed other faint, blue compact objects at great distances. Because the blue color indicates a population of young stars, and given their distances, these were thought to be young galaxies. But the Hubble team's findings suggest that a significant proportion of these objects could be clumps of stars not yet formed into galaxies.

That notion will be more readily testable when a new infrared camera is bolted to Hubble early next year. Space dust blocks the particular signature the team detected from the objects' spectra. That they had a dust-free view and that Hubbell's camera had the ability to "see" at the desired wavelength were part of the serendipity, Keel says. The spectral signatures his team wants to look for in the infrared aren't as vulnerable to being blocked by dust. Hence with the new IR camera, more of these objects could be detected and studied.

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