Astronomers have stripped a galaxy near the Big Dipper of its title as "Most Distant Object Known" by using different techniques to make improved estimates of its distance that show it is closer than it first appeared.
The object was first reported last year when a team of scientists identified the faint galaxy, officially called STIS 123627+621755 but referred to informally as "Sharon," in images taken with NASA's Hubble Space Telescope. They inferred a distance of approximately 12.5 billion light years, which would make it the most distant object known. That distance is equivalent to looking back in time to about 600 million years after the Big Bang, just five percent of the current age of the universe.
A team of astronomers led by Dr. Daniel Stern of NASA's Jet Propulsion Laboratory, Pasadena, Calif., reports that new observations show the galaxy is closer than previously believed, likely about 10 billion light years away, corresponding to 3.3.billion years after the Big Bang. That's about 25 percent of the current age of the universe. The findings are reported in the Nov. 30 issue of the journal Nature, along with similar findings from the scientist whose team made last year's estimate of the distance.
Stern and his colleagues showed that the redshift of the galaxy was different than had been originally reported. Redshift, the standard distance measurement used by astronomers, measures how fast an object is moving away from us as the universe expands. The faster it moves away, the more its light shifts to the red part of the spectrum (toward longer wavelengths). In the 1920s, Dr. Edwin Hubble discovered that the faster an object appears to move, the farther away it is.
"The identification of galaxies at extreme distances provides our most direct information on the earliest phases of galaxy formation," said Stern, whose team made the new observations using images obtained at the W.M. Keck Observatory, Mauna Kea, Hawaii. "These great distances make this a challenging endeavor for even the most luminous sources; it's hard for scientists to interpret faint observations of distant galaxies, and occasional misidentifications will occur."
"The universe has been kind," said co-author Dr. Peter Eisenhardt, also of JPL. "Distant objects have a simple signature -- they are dark at shorter, bluer wavelengths, and abruptly 'turn on' where their light is too red to be absorbed by hydrogen clouds near them. By measuring the wavelength where this 'turn on' occurs, we are able to calculate the distance."
"Basically, the colors of this galaxy are completely inconsistent with it being extremely distant," explained co- author Dr. Hyron Spinrad, an astrophysics professor at the University of California, Berkeley.
With this galaxy's distance debunked, the new titleholder for most distant object in the universe is a quasar identified by astronomers in September 2000.
In addition to Stern, Eisenhardt and Spinrad, the team also includes Steve Dawson of U.C. Berkeley; Dr. Adam Stanford of the University of California, Davis; Drs. Wil van Breugel and Wim de Vries of Lawrence Livermore National Laboratory, Livermore, Calif.; and Dr. Arjun Dey of the Kitt Peak National Observatory near Tucson, Ariz.
The discovery last year, which led to the now-cancelled title of "Most Distant Object," was made by a team from the State University of New York, Stony Brook, led by Dr. Hsiao-Wen Chen.
The W.M. Keck Observatory is sponsored by the California Institute of Technology in Pasadena, NASA, and the University of California, and managed by the California Association for Research in Astronomy, Kamuela, Hawaii. JPL, a NASA center, is managed by Caltech.