A new
method for measuring cosmic distances could pinpoint objects in the universe up
to 300 million light-years away and beyond.
The
just-realized technique was announced today at a meeting of the American
Astronomical Union in Pasadena, Calif., and could help astronomers in their
quest to track the universe's expansion rate.
Until now,
astronomers have partly relied on giant stars called short-period cepheids that
brighten and dim every few days to calculate distances to objects in the
universe. This light
blinking directly relates to the star's true brightness, and astronomers
can compare the true and apparent luminosity (as seen from Earth) to determine
the distance
to that object. But beyond 100 million light-years from Earth, the stars'
signals get lost among other bright stars.
(A
light-year is the distance light
will travel in a year, which is about 6 trillion miles, or 10 trillion km.)
The new
method involves so-called ultra long period cepheids (ULP cepheids), which are
much brighter and so stand out at even farther distances.
Krzysztof
Stanek of Ohio State University and his colleagues searched the literature,
finding records for 18 such ULP cepheids, ranging from 12 to 20 times the mass
of the sun and located in nearby galaxies. The distances to these nearby
galaxies are well known, so the astronomers used that knowledge to calibrate
the distance to the ULP cepheids.
They found
that they could use ULP cepheids to determine distance with a 10 to 20 percent
error, a rate typical of other methods used for measuring cosmic distances. The
researchers hope to reduce that error as more ULP cepheids are recorded.
Now, the
researchers are using the Large Binocular Telescope in Tucson, Ariz., to look for more ULP cepheids. Stanek said they've found a few good candidates in
the galaxy M81, but those results have yet to be confirmed.
The research was funded by the National
Science Foundation.
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