That wide range of values for the Hubble Constant – combined with current knowledge about the universe’s shape and density – results in estimates that the universe is about 8 billion to 13 billion years old, with a corresponding range in size, Kulkarni said.
"If we can get [accurate] distances to more Cepheids, then I think those camps will disappear," he added.
The researchers used the $4 million Palomar Testbed Interferometer. The device incorporates several technical improvements as it combines infrared light collected by a pair of small telescopes located 361 feet (110 meters) apart at
Palomar Observatory, east of San Diego, California.
The Palomar Testbed Interferometer is comprised of 16-inch telescopes in rail sheds at right and left (behind trees), plus a control building (center), at Palomar Observatory in California.
Scientists used the technique to directly measure the expansion and contraction of the supergiant Cepheid
variable star Zeta Geminorum. They determined Zeta Gem ranged between 59 and 65 times the diameter of our sun, or from a contracted diameter of about 51 million miles (82 million kilometers) to an expanded diameter of 56 million miles (90 million kilometers).
Like measuring lunar basketballs
Those measurements, plus the fact Zeta Gem pulses once every 10.15 days, allowed researchers to determine its distance from Earth is 336 parsecs, or 1,095 light-years, which is equal to 6,441 trillion miles (10,365 trillion kilometers).
At that distance, measuring Zeta Gem is like an earthbound observer seeing 10 basketballs lined up on the moon and being able to detect one basketball’s removal, Lane said.
Zeta Gem is in our own
Milky Way Galaxy. So accurately measuring its distance represents only the bottom rung on a cosmic distance scale or "ladder" in which astronomers try to determine distances to increasingly faraway Cepheid stars.
"We have taken one of the nearest Cepheids and measured its distance in a way most astronomers would agree is a fundamental measurement," Kulkarni said. "That’s good because you don’t want to climb a ladder and slip on the first rung. We’ve fixed up the first rung of the cosmic-distance ladder."
Tyler Nordgren, of the U.S. Naval Observatory Flagstaff Station in Arizona, praised the study as "an excellent job" and "the first unambiguous detection of the pulsating diameter of a Cepheid variable star."
It also is part of a "
continuing revolution in telescope resolution," in which telescopes can detect finer and finer detail, Nordgren wrote in a commentary accompanying the study.
Nordgren said the Caltech team’s observations "provide a new and simple method for determining the distance to more Cepheids at larger distances."
A shrinking margin of error
Astronomers calculate the Hubble Constant by observing the "Doppler shift" in the color of light galaxies emit, determining how fast galaxies are moving away from us. Then, they combine that with the distances to those galaxies, as measured using Cepheid stars.
Existing methods have a 30-percent to 50-percent margin of error for measuring the distance to a single Cepheid, although measuring numerous Cepheids sharply reduces that margin, Lane said.
The new method now has a 15-percent maximum error margin for measuring distance to one Cepheid, but that should drop to less than 3 percent when the method is used with bigger, advanced interferometers, he added.
Those include the Navy Prototype Optical Interferometer, being developed in Flagstaff, and Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) interferometer. That device, on Mount Wilson northeast of Los Angeles, will be dedicated October 4.
The Palomar interferometer – designed by Mark Colavita and Michael Shao at Jet Propulsion Laboratory – is testing methods that will be used when scientists link the two 33-foot (10-meter)
Keck telescopes in Hawaii next year.
Lane said the previous indirect methods of measuring a Cepheid’s changing size included observing how the wavelength of starlight was changed by the Doppler shift and star temperatures as the star swelled and shrank.
The Palomar interferometer directly measures a Cepheid’s "angular diameter," or apparent size. For example, a basketball’s angular diameter is larger when you hold it right in front of your nose than when you hold it at arm’s length.
Although each telescope has a 16-inch (40-centimeter) mirror, when linked they act like a single telescope with a 361-foot (110-meter) mirror. That means the interferometer – which produces graphs, not pictures – detects much smaller features, such as a Cepheid’s 10-percent change in size, Lane said.
The distance to the star was calculated by dividing its change of size in degrees (as measured by the interferometer) to its change of size in miles or kilometers (as measured by the Doppler shift of starlight).
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