archive: SETI HUBBLE COMPLETES EIGHT-YEAR EFFORT TO MEASURE EXPANDING
SETI HUBBLE COMPLETES EIGHT-YEAR EFFORT TO MEASURE EXPANDING
Larry Klaes ( email@example.com )
Tue, 25 May 1999 12:50:40 -0400
>Date: Tue, 25 May 1999 12:30:14 -0400 (EDT)
>Subject: HUBBLE COMPLETES EIGHT-YEAR EFFORT TO MEASURE EXPANDING UNIVERSE
>Headquarters, Washington, DC May 25, 1999
>Goddard Space Flight Center, Greenbelt, MD
>Space Telescope Science Institute, Baltimore, MD
>HUBBLE COMPLETES EIGHT-YEAR EFFORT
>TO MEASURE EXPANDING UNIVERSE
> The Hubble Space Telescope Key Project Team today announced
>that it has completed efforts to measure precise distances to far-
>flung galaxies, an essential ingredient needed to determine the
>age, size and fate of the universe.
> "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
> 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 Hubble's constant at 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 light-years
>away from Earth.
> "The truth is out there, and we will find it," said Dr.
>Robert Kirshner of Harvard University. "We used to disagree by a
>factor of two; now we are just as passionate about ten percent. A
>factor of two is like being unsure if you have one foot or two.
>Ten percent is like arguing about one toe. It's a big step
>forward." Added Robert Kennicutt of the University of Arizona, a
>co-leader of the team: "Things are beginning to add up. The
>factor-of-two controversy is over."
> 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
> Combining Hubble's constant measurement with estimates for
>the density of the universe, the team determined that the universe
>is approximately 12 billion years old -- similar to the oldest
>stars. This discovery clears up a nagging paradox that arose from
>previous age estimates. The researchers emphasize that the age
>estimate holds true if the universe is below the so-called
>'critical density' where it is delicately balanced between
>expanding forever or collapsing. Alternatively, the universe is
>pervaded by a mysterious 'dark force' pushing the galaxies farther
>apart, in which case the Hubble measurements point to an even
> 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.
> - end -
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