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Sept. 24, 1999

Kathleen Burton

NASA Ames Research Center, Moffett Field, CA

(Phone: 650/604-1731 or 650/604-9000)



Dr. Eyal Maoz of NASA Ames Research Center, Moffett Field, CA, and astrophysicists from a variety of U.S. and Canadian institutions have found evidence suggesting that the universe may be younger than scientists had previously thought, and that it is expanding faster than expected. Their findings are reported in the Sept. 23 issue of Nature magazine.

Current estimates put the age of the universe at about 15 billion years. Maoz' research indicates the universe may be as young as 12 billion years, nearly the same age as its oldest stars. This implied relatively low age of the universe revives an old paradox in the field of astrophysics that the universe seems to be younger than some of the stars in it. The finding suggests that a revision of the cosmological model may be required.

Maoz and his team used the Hubble Space Telescope to observe the pulsing of giant stars called 'Cepheid variables' in the galaxy NGC4258. Researchers used a standard "Cepheid measurement" technique that allowed them to measure the distance from Earth to the galaxy. However, this measurement was different from another independent, highly accurate distance determination to that galaxy made using masers (the microwave equivalent of lasers), which are located at the galaxy center and orbiting a supermassive black hole.

A revision of the standard Cepheid measurement method would mean that estimates for the age of the Universe would have to be revised downwards by 10-15%, experts say.

Measuring galactic distances using Cepheid variables has been a standard since 1929. They are useful because their rate of pulsation is closely linked to their brightness. This means that a galaxys' apparent brightness can be used to gauge its distance from Earth.

Maoz and his colleagues used the Cepheid method to estimate the distance from Earth to the benchmark NGC4258 galaxy as 8.1 megaparsecs (Mpc), significantly farther than the geometric estimates derived by recent estimates. (One Mpc is equivalent to approximately three million light years.)

"We discovered a considerable discrepancy between the maser-based and Cepheid-based distance," Maoz said. "The bottom line is that it seems that galaxy distances may have been consistently overestimated by about 12%. This would imply that the universe is expanding faster than expected, and the age of the universe is lower by a similar factor."



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