By applying a technique called spatial scanning to
an age-old method for gauging distances called astronomical parallax, scientists
now can use NASA’s Hubble Space Telescope to make precision distance
measurements 10 times farther into our galaxy than previously
possible.
Image Credit:
NASA/ESA, A.Feild/STScI
Using NASA's Hubble Space Telescope, astronomers now can precisely measure
the distance of stars up to 10,000 light-years away -- 10 times farther than
previously possible.
Astronomers have developed yet another novel way to use the 24-year-old space
telescope by employing a technique called spatial scanning, which dramatically
improves Hubble's accuracy for making angular measurements. The technique, when
applied to the age-old method for gauging distances called astronomical
parallax, extends Hubble's tape measure 10 times farther into space.
"This new capability is expected to yield new insight into the nature of dark
energy, a mysterious component of space that is pushing the universe apart at an
ever-faster rate," said Noble laureate Adam Riess of the Space Telescope Science
Institute (STScI) in Baltimore, Md.
Parallax, a trigonometric technique, is the most reliable method for making
astronomical distance measurements, and a practice long employed by land
surveyors here on Earth. The diameter of Earth's orbit is the base of a triangle
and the star is the apex where the triangle's sides meet. The lengths of the
sides are calculated by accurately measuring the three angles of the resulting
triangle.
Astronomical parallax works reliably well for stars within a few hundred
light-years of Earth. For example, measurements of the distance to Alpha
Centauri, the star system closest to our sun, vary only by one arc second. This
variance in distance is equal to the apparent width of a dime seen from two
miles away.
Stars farther out have much smaller angles of apparent back-and-forth motion
that are extremely difficult to measure. Astronomers have pushed to extend the
parallax yardstick ever deeper into our galaxy by measuring smaller angles more
accurately.
This new long-range precision was proven when scientists successfully used
Hubble to measure the distance of a special class of bright stars called Cepheid
variables, approximately 7,500 light-years away in the northern constellation
Auriga. The technique worked so well, they are now using Hubble to measure the
distances of other far-flung Cepheids.
Such measurements will be used to provide firmer footing for the so-called
cosmic "distance ladder." This ladder's "bottom rung" is built on measurements
to Cepheid variable stars that, because of their known brightness, have been
used for more than a century to gauge the size of the observable universe. They
are the first step in calibrating far more distant extra-galactic milepost
markers such as Type Ia supernovae.
Riess and the Johns Hopkins University in Baltimore, Md., in collaboration
with Stefano Casertano of STScI, developed a technique to use Hubble to make
measurements as small as five-billionths of a degree.
To make a distance measurement, two exposures of the target Cepheid star were
taken six months apart, when Earth was on opposite sides of the sun. A very
subtle shift in the star's position was measured to an accuracy of 1/1,000 the
width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8
megapixels total. A third exposure was taken after another six months to allow
for the team to subtract the effects of the subtle space motion of stars, with
additional exposures used to remove other sources of error.
Riess shares the 2011 Nobel Prize in Physics with another team for his
leadership in the 1998 discovery the expansion rate of the universe is
accelerating -- a phenomenon widely attributed to a mysterious, unexplained dark
energy filling the universe. This new high-precision distance measurement
technique is enabling Riess to gauge just how much the universe is stretching.
His goal is to refine estimates of the universe's expansion rate to the point
where dark energy can be better characterized.
The Hubble Space Telescope is a project of international cooperation between
NASA and the European Space Agency. NASA's Goddard Space Flight Center in
Greenbelt, Md., manages the telescope. STScI conducts Hubble science operations.
STScI is operated for NASA by the Association of Universities for Research in
Astronomy, Inc., in Washington.
For images and more information about Hubble, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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