Hubble measures the expanding Universe
Right: A NASA Hubble Space Telescope (HST) view of the magnificent spiral galaxy NGC 4603, the most distant galaxy in which a special class of pulsating stars called Cepheid variables have been found. Researchers found 36-50 Cepheids and used their observed properties to securely determine the distance to NGC 4603. Observations of distant Cepheids such as those in NGC 4603 also help astronomers to precisely measure the expansion rate of the Universe (more information).
"Before Hubble, astronomers could not decide if the universe was 10 billion or 20 billion years old," said team leader Wendy Freedman of the Observatories of the Carnegie Institution of Washington. "The size scale of the universe had a range so vast that it didn't allow astronomers to confront with any certainty many of the most basic questions about the origin and eventual fate of the cosmos. After all these years, we are finally entering an era of precision cosmology. Now we can more reliably address the broader picture of the universe's origin, evolution and destiny."
The team's precise measurements are the key to learning about the universe's rate of expansion, called Hubble's constant. Measuring Hubble's constant was one of the three major goals for NASA's Hubble Space Telescope when it was launched in 1990.
For the past 70 years astronomers have sought a precise measurement of Hubble's constant, ever since astronomer Edwin Hubble realized that galaxies were rushing away from each other at a rate proportional to their distance, i.e. the farther away, the faster the recession. For many years, right up until the launch of the Hubble telescope -- the range of measured values for the expansion rate was from 50 to 100 kilometers per second per megaparsec (a megaparsec, or mpc, is 3.26 million light years).
The team measured the Hubble Constant to be 70 km/sec/mpc, with an uncertainty of 10 percent. This means that a galaxy appears to be moving 160,000 miles per hour faster for every 3.3 million light-years away from Earth.
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The team used the Hubble telescope to observe 18 galaxies out to 65 million light-years. They discovered almost 800 Cepheid variable stars, a special class of pulsating star used for accurate distance measurement. Although Cepheids are rare, they provide a very reliable "standard candle" for estimating intergalactic distances. The team used the stars to calibrate many different methods for measuring distances.
"Our results are a legacy from the Hubble telescope that will be used in a variety of future research," said Jeremy Mould of the Australian National University, also a co-leader of the team. "It's exciting to see the different methods of measuring galaxy distances converge, calibrated by the Hubble Space Telescope."
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The universe's age is calculated using the expansion rate from precise distance measurements, and the calculated age is refined based on whether the universe appears to be accelerating or decelerating, given the amount of matter observed in space. A rapid expansion rate indicates the universe did not require as much time to reach its present size, and so it is younger than if it were expanding more slowly.
The Hubble Space Telescope Key Project Team is an international group of 27 astronomers from 13 different U.S. and international institutions. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt, MD.
HUBBLE COMPLETES EIGHT-YEAR EFFORT TO MEASURE EXPANDING UNIVERSE, NASA HQ press release, May 25, 1999
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
More Space Science Headlines - NASA research on the web
NASA's Office of Space Science press releases and other news related to NASA and astrophysics
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