Studies suggest galaxies formed very early.
University of Hawaii astronomers Esther M. Hu and Susan E. Ridgway came up with a surprising answer when they began searching for distant, youthful galaxies in the neighborhood of a quasar.
Though the glow of hot, newborn stars would suffuse a young galaxy with blue light, the Honolulu-based team figured that some of the galaxies in their survey might appear red. A cocoon of dust surrounding a newborn galaxy would absorb the blue light and provide a reddish tinge, as would the red glow from a high concentration of ionized gas.
Hu and Ridgway did see red--and how. Two galaxies in their near-infrared and visible-light survey appear three to four times redder than any galaxy ever observed at these wavelengths, they report in the April ASTRONOMICAL JOURNAL.
To the researchers' puzzlement, however. observations with two telescopes atop Hawaii's Mauna Kea revealed that neither dust nor the glow of ionized gas could explain the galaxies' red appearance. For example, the galaxies abruptly increased in brightness over a narrow range of wavelengths instead of brightening gradually, as they would if dust had reddened them.
If dust or ionized gas didn't color the galaxies, what did? Hu and Ridgway suggest that instead of being newborns, the two galaxies are actually old -- and thus intrinsically red.
The abrupt increase in brightness, they note, resembles the pattern of emissions from elderly, elliptical galaxies near the Milky Way -- with one significant difference. The nearby ellipticals show a surge in brightness in visible light, whereas the two red galaxies show the same jump at a longer, near-infrared wavelength.
That discrepancy could have an intriguing explanation: The red galaxies have a structure identical to that of nearby ellipticals, yet they may lie so far away that the visible light they emit has been stretched, or redshifted, to the infrared. Indeed, Hu and Ridgway propose that light now reaching Earth from these galaxies reveals how the bodies appeared when the universe was half its current age.
The researchers don't have the spectroscopic measurements to prove where the two galaxies actually lie. But if they're right, it would indicate that some galaxies already had old, red stars when the cosmos was very young.
According to Hu, this suggests that some galaxies must have formed when the universe was only about 5 percent of its current age. If the red galaxies are representative of others in the universe, this finding could set a minimum age for the universe of about 15 billion years, she says.
In a separate, unpublished finding, another group of astronomers has discovered what appears to be the most distant galaxy yet observed, SCIENCE NEWS has learned. According to Steve Rawlings and Mark Lacy of the University of Oxford in England and their coworkers, several lines of evidence suggest that the radio galaxy dubbed 8C 1435+635 lies some 12 billion light-years from Earth.
The faintness of the galaxy in the infrared, its brightness at radio wavelengths, and the detection in visible light of what appears to be the redshifted glow of hydrogen gas all indicate that the team sees the galaxy as it appeared when the universe was just 8 percent of its current age, Rawlings says.
The discovery, he adds, suggests that this galaxy, and perhaps others, had begun making stars only a billion years after the birth of the cosmos.
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|Title Annotation:||astronomical research on galactic redshifts, most distant known galaxy|
|Article Type:||Brief Article|
|Date:||May 14, 1994|
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