NASA's Infrared Observatory Measures Expansion of Universe

Oct. 3, 2012

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

RELEASE: 12-343

NASA'S INFRARED OBSERVATORY MEASURES EXPANSION OF UNIVERSE

WASHINGTON -- Astronomers using NASA's Spitzer Space Telescope have
announced the most precise measurement yet of the Hubble constant, or
the rate at which our universe is stretching apart.

The Hubble constant is named after the astronomer Edwin P. Hubble, who
astonished the world in the 1920s by confirming our universe has been
expanding since it exploded into being 13.7 billion years ago. In the
late 1990s, astronomers discovered the expansion is accelerating, or
speeding up over time. Determining the expansion rate is critical for
understanding the age and size of the universe.

Unlike NASA's Hubble Space Telescope, which views the cosmos in
visible light, Spitzer took advantage of long-wavelength infrared
light to make its new measurement. It improves by a factor of 3 on a
similar, seminal study from the Hubble telescope and brings the
uncertainty down to 3 percent, a giant leap in accuracy for
cosmological measurements. The newly refined value for the Hubble
constant is 74.3 �� 2.1 kilometers per second per megaparsec. A
megaparsec is roughly 3 million light-years.

"Spitzer is yet again doing science beyond what it was designed to
do," said project scientist Michael Werner at NASA's Jet Propulsion
Laboratory in Pasadena, Calif. Werner has worked on the mission since
its early concept phase more than 30 years ago. "First, Spitzer
surprised us with its pioneering ability to study exoplanet
atmospheres," said Werner, "and now, in the mission's later years, it
has become a valuable cosmology tool."

In addition, the findings were combined with published data from
NASA's Wilkinson Microwave Anisotropy Probe to obtain an independent
measurement of dark energy, one of the greatest mysteries of our
cosmos. Dark energy is thought to be winning a battle against
gravity, pulling the fabric of the universe apart. Research based on
this acceleration garnered researchers the 2011 Nobel Prize in
physics.

"This is a huge puzzle," said study lead author Wendy Freedman of the
Observatories of the Carnegie Institution for Science in Pasadena.
"It's exciting that we were able to use Spitzer to tackle fundamental
problems in cosmology: the precise rate at which the universe is
expanding at the current time, as well as measuring the amount of
dark energy in the universe from another angle." Freedman led the
ground-breaking Hubble Space Telescope study that earlier had
measured the Hubble constant.

Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in
Washington, said infrared vision, which sees through dust to provide
better views of variable stars called cepheids, enabled Spitzer to
improve on past measurements of the Hubble constant. "These pulsating
stars are vital rungs in what astronomers call the cosmic distance
ladder: a set of objects with known distances that, when combined
with the speeds at which the objects are moving away from us, reveal
the expansion rate of the universe," said Wahlgren.

Cepheids are crucial to the calculations because their distances from
Earth can be measured readily. In 1908, Henrietta Leavitt discovered
these stars pulse at a rate directly related to their intrinsic
brightness.

To visualize why this is important, imagine someone walking away from
you while carrying a candle. The farther the candle traveled, the
more it would dim. Its apparent brightness would reveal the distance.
The same principle applies to cepheids, standard candles in our
cosmos. By measuring how bright they appear on the sky, and comparing
this to their known brightness as if they were close up, astronomers
can calculate their distance from Earth.

Spitzer observed 10 cepheids in our own Milky Way galaxy and 80 in a
nearby neighboring galaxy called the Large Magellanic Cloud. Without
the cosmic dust blocking their view at the infrared wavelengths seen
by Spitzer, the research team was able to obtain more precise
measurements of the stars' apparent brightness, and thus their
distances. These data opened the way for a new and improved estimate
of our universe's expansion rate.

"Just over a decade ago, using the words 'precision' and 'cosmology'
in the same sentence was not possible, and the size and age of the
universe was not known to better than a factor of two," said
Freedman. "Now we are talking about accuracies of a few percent. It
is quite extraordinary."

The study appears in the Astrophysical Journal. Freedman's co-authors
are Barry Madore, Victoria Scowcroft, Chris Burns, Andy Monson, S.
Eric Person and Mark Seibert of the Observatories of the Carnegie
Institution and Jane Rigby of NASA's Goddard Space Flight Center in
Greenbelt, Md.

For more information about Spitzer, visit:

http://www.nasa.gov/spitzer


-end-



To subscribe to the list, send a message to:
hqnews-subscribe@mediaservices.nasa.gov
To remove your address from the list, send a message to:
hqnews-unsubscribe@mediaservices.nasa.gov