Findings call universe’s size into question


By Lauren Nisbet
Thursday, January 27, 2011
The way we understand the size of the universe is changing as a result of research done by an international team, which included Pauline Barmby, an astronomer in Western’s Department of Physics and Astronomy.
“The biggest problem in astronomy is that when we look at something in the sky, we don’t know how far away it is,” Barmby says. “Measuring distances is important to understanding the properties of the things in the universe.”
The study examined Cepheid variable stars, which are a type of standard candle used to determine distances in the universe. Measuring the brightness of a candle that is closer against that of an identical candle that is farther away can help to establish the distance between them. This particular class of standard candles known as Cepheids pulsates, getting brighter and dimmer over time, helps astronomers determine their luminosity.
This calculation was famously performed by astronomer Edwin Hubble in 1924, leading to the revelation that our galaxy is just one of many in a vast cosmic sea. Cepheids also helped in the discovery that our universe is expanding, and galaxies are drifting apart.
Barmby’s study, utilizing NASA's Spitzer Space Telescope, found evidence some Celpheids are losing mass, a factor which could produce inaccurate measurements. “It doesn’t mean that everything we thought we knew is wrong, but if you want to do the best possible job, this effect needs to be considered.”
Follow-up studies have shown that 25 per cent of these stars are shrinking.
Astronomers have studied the mass of stars for a long time, but the appearance of discrepancies between different methods of measurement is what led to Barmby’s search for evidence that stars might actually be losing mass. “If one measurement examined the stars when they were younger and the other when they were older, then the disagreement would make more sense.”
 “By taking images with an infrared telescope we can see the dust in the mass that is being lost, which allows us to measure it.”
The infrared camera used is called the IRAC or ‘infrared array camera’ and is part of NASA’s Spitzer Space Telescope. Barmby was also involved in the construction of this camera at the time of the telescope’s launch in 2003.
By examining astronomical objects like standard candles, astronomers are not only able to gain insight into the state of the universe, but also the Earth itself. “Understanding the universe gives us a better understanding of why the Earth is the way it is. If we want to understand where we come from, we need to understand the world around us,” Barmby says. “Plus, it’s just cool.”
Massimo Marengo of Iowa State University was lead author of the study on the discovery appearing in the Astronomical Journal. Barmby was lead author of the follow-up Cepheid study published online Jan. 6 in the Astronomical Journal.
Other authors of this study include N. R. Evans and G.G. Fazio of the Harvard-Smithsonian Center for Astrophysics; L.D. Matthews of Harvard-Smithsonian and the Massachusetts Institute of Technology Haystack Observatory; G. Bono of the Università di Roma Tor Vergata and the INAF-Osservatorio Astronomico di Roma in Italy; D.L. Welch of the McMaster University; M. Romaniello of the European Southern Observatory, Germany; D. Huelsman of Harvard-Smithsonian and University of Cincinnati; and K. Y. L. Su of the University of Arizona.

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