April 29, 2008 -- They may have been small, but some of the universe's first galaxies sure packed a wallop.
Astronomers have discovered nine baby beasts, each of which would fit quite contently in just the hub of our own rather modest Milky Way galaxy, stuffed with as many stars as galaxies of more recent vintage.
"Seeing the compact sizes of these galaxies is a puzzle," said Yale University's Pieter van Dokkum, lead author of a paper on the discovery appearing in this month's Astrophysical Journal Letters.
Scientists estimate the early galaxies would have needed to expand five times over to reach the stately proportions of their more modern kin. Colliding with each other might be one way to build up real estate, but that's probably not the whole answer, van Dokkum said.
"It is not yet clear how they would build themselves up to become the large galaxies we see today," he added.
Astronomers using the Hubble Space Telescope and the Keck Observatory on Mauna Kea, Hawaii, found nine compact galaxies that formed about 11 billion years ago, less than 3 billion years after the birth of the universe.
They are small, like most early star-forming galaxies, measuring no more than 5,000 light-years in diameter.
But unlike previous finds, these clusters weigh as much as the Milky Way, with a mass equivalent to about 200 billion suns.
Scientists suspect dark matter played a key role in the galaxies' formation. They theorize that dark matter, which accounts for most of the mass in the universe, trapped pockets of hydrogen generated in the universe's birth. Stoked by dark matter's gravitational hands, the hydrogen began swirling, igniting the engines of star formation.
Not only are the baby galaxies obese with stars. The broods whip around their galactic disks at a heady 275 miles per second. That's about twice as fast as grownup galaxies.
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