Sep 27, 1999

The Bouncing Baby Universe





Researchers find evidence that the Universe may be younger than previously thought




VLA image of NGC 4258
September 27, 1999: 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 September 23 issue of Nature magazine.


Many 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 could revive an old paradox in the field of astrophysics that the universe seems to be younger than some of the stars in it.

Above: This optical image shows the core region of galaxy NGC 4258. By measuring the motions of microwave lasers in a disk orbiting a central supermassive black hole, astronomers can estimate the distance to this galaxy very accurately. By comparing maser distance measurements with Cepheid distance estimates of NGC 4258, Maoz et al realized that the widely used Cepheid distance scale overestimates galaxy distances. That means the Universe may be younger than previously thought. Image Credit: NRAO

Hubble Constant image
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. This means that the Cepheid distance scale may need tweaking.

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.



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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 galaxy's 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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The Expansion Rate and Size of the Universe., W.L. Freedman. From Scientific American, March 1998.

The Shapley-Curtis Debate in 1920.What is the scale of the Universe? What was the debate, why was it important, and how was it resolved? From Astronomy Picture of the Day.

75 years later: the 1996 debate on the size and age of the Universe. What is the scale of the Universe? What was the debate, why was it important, and how was it resolved? From Astronomy Picture of the Day.

Edwin Powell Hubble -- Biographical Memoir

The Hubble Constant -- from a NASA Space Science Short

Hubble's Constant and the Expanding Universe (I) -- Astronomy Picture of the Day, May 13, 1996

Hubble's Constant and the Expanding Universe (II) -- Astronomy Picture of the Day, May 14, 1996

Edwin Hubble Discovers the Universe -- Astronomy Picture of the Day, Feb 17, 1996

The Cepheids of M100 -- Astronomy Picture of the Day, Jan 10, 1996

PG 1115: A Ghost of Lensing Past -- Astronomy Picture of the Day, Nov 2, 1998

Cosmic Gamma-ray Bursts -- News and Research

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