LLNL astrophysicists discover most distant galaxy known is not as far away as once believed

November 28, 2000

LIVERMORE, Calif.--Lawrence Livermore National Laboratory astrophysicists Wil Van Breugel and Wim De Vries, with colleagues from several universities and observatories, have stripped a galaxy near the Big Dipper, commonly known as STIS 123627+621755, of its title as the "Most Distant Object Known" by showing that the initial distance estimate was incorrect.

The findings, which will be published in the Nov. 30 issue of Nature, are based on very deep images obtained using the world's largest W. M. Keck Observatory's 10-m telescopes in Hawaii earlier this year. A team of SUNY-Stony Brook astronomers, led by Hsiao-Wen Chen, reported observations of this same object using the NASA's Hubble Space Telescope. Based on the extremely red colors of STIS 123627+621755 and a single emission line in its spectrum, thought to be hydrogen, the team estimated that this was a galaxy at an approximate distance of 12.5 billion light years. This implied that the galaxy should essentially be invisible in the optical and relatively bright at near-infrared wavelengths.

However, these predictions were not confirmed by the deep images obtained by van Breugel and collaborators. In fact, the galaxy was detected in optical light at a level that was 100 times brighter than expected and remained invisible in the infrared. The galaxy was much bluer than initially thought. The faint emission line observed by Chen's team is therefore more likely to be based on oxygen instead of hydrogen gas. This resulted in a much smaller distance estimate of 9.8 billion light years and the re-classification of the object as a small dwarf galaxy, similar to Earth's neighboring Magellanic Clouds visible from the Southern Hemisphere.

"At LLNL we have been at the forefront of distant galaxy searches for many years, and we realize that sometimes a difficult measurement may turn out to be in error," van Breugel said. "We hope that our own record of a galaxy, which emits powerful radio waves at a distance of 12.3 billion light years, will stand the test of time."

The 'hunt' for the most distant galaxies has been important since the first major telescopes were built. It led Edwin Hubble in 1924 to conclude that the Universe expands, and later resulted in the now commonly held belief that the Universe started with a hyper energetic "Big Bang" about 13.1 billion years ago. With much more sensitive detectors and larger telescopes now available, the most distant galaxies are beacons for measuring how galaxies and the Universe formed. Even with modern instruments the most distant galaxies are very difficult to detect and occasional misidentifications can occur.

With the estimated distance of 12.5 billion light years for STIS 123627+621755 no longer correct, the new titleholder for the most distant object known belongs to a quasar, an active black hole at 12.4 billion light years. The race to find the most distant objects in the Universe is very tight. It depends not only on accurate measurements, but also on assumptions of how we think the "Big Bang" occurred.

Besides Van Breugel and De Vries of LLNL, the team also includes Daniel Stern and Peter Eisenhardt of the Jet Propulsion Laboratory; Hyron Spinrad and Steve Dawson of the University of California Berkeley; Adam Stanford of the University of California Davis and Arjun Dey of the Kitt Peak National Observatory.
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Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy.

DOE/Lawrence Livermore National Laboratory

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