Princeton researchers join dark energy mission

Three Princeton researchers will join a mission to study dark energy and dark matter as participants in the European Space Agency's (ESA) planned Euclid space telescope project. The Princeton astrophysicists will work as part of team led by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

The Euclid mission is a space telescope designed to probe the mysteries of dark energy and dark matter. NASA is a partner in the Euclid mission, currently scheduled to launch in 2020. 

The Princeton researchers are David Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation; Michael Strauss, professor of astrophysical sciences; and Robert Lupton, senior research scientist in the Department of Astrophysical Sciences. They will contribute to science planning and data analysis as part of JPL's 43-member science team, 29 of whom were recently appointed by NASA.


This artist's concept shows the Euclid spacecraft. The telescope will launch to an orbit around the sun-Earth Lagrange point L2. The Lagrange point is a location where the gravitational pull of two large masses, the sun and Earth in this case, precisely equals the force required for a small object, such as the Euclid spacecraft, to maintain a relatively stationary position behind Earth as seen from the sun. (Image courtesy of ESA/C. Carreau)

"Euclid is a space-based telescope so its view will not be affected by the Earth's atmosphere," Strauss said. "Conducting surveys of the galaxies from space will allow Euclid scientists to measure their properties in greater detail than can be done from Earth." 

The team is led by JPL scientist Jason Rhodes, who earned his Ph.D. at Princeton in 1999. JPL will provide 16 advanced infrared detectors and four spares for one of two instruments planned for the mission.

The JPL team is the largest of three U.S. teams participating in Euclid. The others are led by Ranga-Ram Chary of the Infrared Processing and Analysis Center at the California Institute of Technology, and Alexander Kashlinsky of NASA's Goddard Space Flight Center, Greenbelt, Md., with three and seven members, respectively.

The Euclid Consortium is an international body of 1,000 members that will oversee the development of the instruments and analyze the science data jointly.

"Understanding the hidden contents of the universe and the nature of the dark energy will require the collaboration of astronomers and engineers around the world," Rhodes said.

Euclid will observe up to 2 billion galaxies occupying more than one-third of the sky with the goal of better understanding the contents of our universe. Everyday matter that we see around us — for example in tables and chairs, people, and stars — makes up only a few percent of the matter in the cosmos. A larger amount of the cosmos, about 24 percent, is thought to consist of dark matter, an invisible substance that does not reflect or emit any light but exerts a gravitational tug on other matter. 

The majority of the universe, about 73 percent, is thought to be filled with dark energy, something even more mysterious than dark matter. Whereas dark matter pulls through its gravity, dark energy is thought to be a repulsive force pushing matter apart. Scientists think dark energy may be responsible for stretching our universe apart at ever-increasing speeds, an observation that earned the Nobel Prize in physics in 2011.

Euclid scientists will use two different methods to make the most precise measurements yet of our "dark" universe. The first method, called weak lensing, involves analyzing the shapes of billions of galaxies. When dark matter lies in front of galaxies, it can't be seen but its gravity distorts the light from the galaxies behind it. More dark matter will lead to slightly larger distortions. By measuring these minute distortions, scientists can understand the amount and distribution of the dark matter between the Earth and these galaxies. 

Changes in these dark matter structures over time are governed by an interplay between the attractive force of gravity and the repulsive force of dark energy. Thus, studying galaxy shapes reveals information about both dark matter and dark energy.  

The second method, called galaxy clustering or baryon acoustic oscillations, will serve as an independent measurement of dark energy. Early in the universe, galaxies were imprinted with a standard distance between them. This distance — referred to as a standard ruler — expands as the universe itself expands. By making precise measurements of the distances of tens of millions of galaxies, the scientists will be able to chart this expansion and learn more about the dark energy driving it.

The U.S. science team will employ both of these methods, and work together with the rest of the Euclid scientists, to shine light on the darkest riddles of our cosmos. 

Euclid is a European Space Agency mission with science instruments and data analysis provided by the Euclid consortium with important participation from NASA. NASA's Euclid Project Office is based at JPL. JPL will contribute the infrared flight detectors for one of Euclid's two science instruments. NASA Goddard will assist with infrared detector characterization and will perform detailed testing on flight detectors prior to delivery. Three U.S. science teams, led by JPL, Goddard and the Infrared Processing and Analysis Center at Caltech, will contribute to science planning and data analysis. Caltech manages JPL for NASA.