Indian-American part of major breakthrough

Yale University cosmologist Priyamvada Natarajan was part of an international team of astronomers that used a massive galaxy cluster as a cosmic magnifying lens to study the nature of elusive dark energy for the first time. Their findings appeared in August's issue of the prestigious journal Science.

Astronomers employ a variety of methods to study the geometry of the universe in order to study the nature of dark energy -- a mysterious force discovered in 1998 that speeds up the expansion of the universe -- about which precious little is known.

Uncovering the nature of dark energy, which makes up about 72 percent of all the universe's mass and energy and which is said to ultimately determine its face, is considered one of the holy grails of modern-day cosmology.

When combined with existing techniques, the team's findings are expected to significantly improve current measurements of the universe's mass and energy content.

The team used gravitational lensing to learn more about this elusive force, especially data taken by the Hubble Space Telescope as well as ground-based telescopes, and analysed images of 34 extremely distant galaxies situated behind Abell 1689, one of the biggest and most massive known galaxy clusters in the universe.

Through the gravitational 'lens' of Abell 1689, the astronomers were able to detect the faint, distant background galaxies -- whose light was bent and projected by the cluster's massive gravitational pull -- in a similar way that the lens of a magnifying lens distorts an object's image. Natarajan, professor, departments of astronomy and physics, and director, graduate studies, department of astronomy, Yale University, said that the way in which the images were distorted gave the astronomers clues as to the geometry of the space that lies between the Earth, the cluster and the distant galaxies.

"The content, geometry and fate of the universe are linked, so if you can constrain two of those things, you learn something about the third," she said.

Natarajan -- who, many believe, is a potential Nobel laureate, and winner of the Rediff.com-owned US newspaper India Abroad's 2009 Face of the Future Award -- explained that using theoretical models of the distribution of both ordinary and dark matter in space, the team had narrowed down the range of current estimates about dark energy's effect on the universe, denoted by the value w, by 30 percent.

The team combined their new technique with other methods, including using supernovae, X-ray galaxy clusters and data from the Wilkinson Microwave Anisotropy Probe spacecraft, to constrain the value for w.

"The contents, geometry and fate of the universe are intricately linked, so accurate knowledge of any two sheds light on the other," Natarajan told rediff.com. "The first piece of observational evidence for the accelerating expansion of the universe came in 1998, from the brightness of supernovae, and since then the quest has been to understand what powers this accelerating expansion."

She said that there were now several observational techniques available to probe the mysterious force known as dark energy that powers the accelerating expansion of the universe, but acknowledged that "all techniques have limitations."

"What we have presented here is a novel one that has very different pitfalls from the others," she continued. "This one is particularly beautiful -- and I am using the word very consciously -- as it derives from the bending of light that is predicted by Einstein's general relativity."

She said the future was very promising for the techniques the team used to study the nature of dark energy "as there are dozens of other clusters that can be used in the same fashion."

Natarajan said, "Personally, I have been gearing up for this work for almost a decade, and I started working on understanding the detailed distribution of dark matter right after I finished my PhD in 1999."

She continued: "To get this to work, we need an accurate mass estimate of the lensing cluster. After establishing my expertise in mapping dark matter with the highest possible degree of precision, I moved on to then using these lenses as cosmic telescopes. My students at Yale and collaborators around the world have been on this quest gathering all the observational data needed to get this project done, and it has been really fun to work with really talented and dedicated people."

Echoing similar sentiments as she expressed in her acceptance speech at the India Abroad award event, Natarajan added, "As human beings, we all have an essential curiosity about the universe, and that's what been so interesting working in cosmology -- there is enormous public interest, excitements and support which is just fantastic. I feel so privileged and fortunate to be able to follow my passion."