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Massive new mapping of the universe could unlock secrets of 'dark energy'

Tuesday, January 8, 2013

LAWRENCE — A researcher at the University of Kansas is playing an important role in BigBOSS, a huge new plan to grasp why the expansion of the universe is accelerating rather than slowing down. This mystery of physics is due to little-understood “dark energy,” which has been calculated to make up roughly 70 percent of the cosmos.

Gregory Rudnick

“The universe used to be thought of slowing down its expansion over time,” said Gregory Rudnick, assistant professor of physics and astronomy at KU. “But in the late ’90s they found that the speed at which the universe is expanding is increasing with time — the universe is accelerating its expansion. There are many competing theories to explain what is driving the acceleration, but at this moment no one really knows.”

For lack of a better term astronomers and physicists have coined the thing that causes the accelerating expansion “dark energy.”

By making a more thorough, detailed, three-dimensional map of a big swath of the universe and extending these measurements 9.2 billion years into the past, it is hoped that several contending theories about dark energy could be ruled out, allowing astronomers to focus on more likely explanations of the enigmatic phenomenon.

“The goal is that this project, which is going to be mapping a third of the entire sky, will make the best measurement of how the universe has changed in its expansion, and that in turn will place very good restraints on any kind of theoretical model that tries to explain this dark energy,” Rudnick said. “Seventy percent of the energy and mass content of the universe is in the form of this dark energy that we can’t see and don’t understand. So it’s a huge question, the biggest unsolved problem in physics — what’s driving the universe’s expansion?”

The BigBOSS project will use the four-meter Mayall telescope at Kitt Peak National Observatory in Arizona, coupled with an innovative new instrument that will rapidly position 5,000 robot-controlled optical fibers onto on galaxies and quasars in the telescope’s view. The fibers will carry the images to a spectrograph that will allow astronomers to measure the distance to distant objects by measuring “redshift,” or the Doppler effect as it applies to light. In just one night, BigBOSS could map as many as 150,000 objects in the night sky.

“It going to enable us to observe many more objects, and observe them with higher precision, than we ever have before,” Rudnick said. “You get the velocity of the object, which tells you about its distance. You get its chemical composition. You can understand how the stars are moving in relation with each other within each galaxy. You can understand the mix of ages of stars in the galaxy — how many old stars versus young stars. And you get the spatial distribution of the galaxies, so if you want to understand from a galaxy evolution perspective how galaxies clump together and how that influences their behavior, this will be unparalleled for that.”

The BigBOSS project primarily aims to utilize a “cosmic yardstick” that is the relic of acoustic ripples in the plasma of the early universe that has the effect of concentrating galaxies at 500-million-light-year intervals. These ripples are known as baryon acoustic oscillations. Because light travels at a fixed speed, the light that reaches Earth from distant objects left those objects when the universe was younger, turning telescopes into literal backward-looking time machines. By measuring the angular size of the baryon acoustic oscillations at different distances, and hence at different points in the universe’s past, the BigBOSS team will measure the rate of growth of the universe over time.

Indeed, aside from giving astronomers a better understanding of dark energy, Rudnick said the high-precision data would useful for cosmologists investigating a wide array of questions. Indeed, while Rudnick is KU’s institutional lead for the BigBOSS project, his own research interest lies in determining the evolution of galaxies. Other KU faculty with an interest in the BigBOSS project include Barbara Anthony-Twarog, Bruce Twarog, Hume Feldman and Danny Marfatia, who pursue research interests ranging from the evolution of stars in our own galaxy to the large scale structure of the universe.

Yet, achieving a better understanding of dark energy is the ultimate goal of the project.

“Who knows what technological spinoffs are going to come from building an instrument like this?” said Rudnick. “But the science is to understand this largest component of the universe that we don’t know about — and it’s kind of uncomfortable that we don’t what 70 percent of the energy comprising the universe is made of. Side projects using the BigBOSS data may even shed light on the nature of dark matter which, in addition to dark energy, constitutes 95 percent of the mass and energy of the universe. Obviously these are huge questions in physics and astronomy. If we think understanding the fundamental nature of the universe is important, than this kind of project is clearly needed.”

Currently, the Gordon & Betty Moore Foundation has funded the BigBOSS project with $2.1 million while the BigBOSS team applies for a larger grant from the U.S. Department of Energy. This important seed funding will permit the construction of critical components that will remove the major technical barriers to the completion of the BigBOSS instrument.