Feature Story | 6-Mar-2023

Rachel Mandelbaum: Then and Now / 2012 Early Career Award Winner

Rachel Mandelbaum’s work uses data from large sky surveys to study the physics governing the second half of the universe’s age

DOE/US Department of Energy

My work focuses on understanding the physics governing the second half of the age of the Universe, using imaging data from large sky surveys.

These sky surveys are undertaken over a period of many years with powerful telescopes. They let us ask questions like “Why has the universe’s expansion started to accelerate in the past ~7 billion years?” Current answers to this question point to “dark energy,” a dominant but mysterious energy component in the universe. 

Data from the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) can help us better answer this and other fundamental questions about the universe – if we have the right tools and methods to accurately analyze the data. More specifically, I work on preparing to measure weak gravitational lensingThis is the tiny but coherent deflections of light from distant galaxies due to the gravitational influence of dark matter and visible matter (such as galaxies) that the light rays pass by on their way to Earth. From there, we learn about the nature and amount of dark energy.

I received the DOE Early Career Award when I was just establishing my research program at Carnegie Mellon University. It enabled me to establish a research group at the forefront of the international weak lensing research community. We were leaders both in preparing for the LSST and in applying our methods to existing datasets (which ultimately determines how we analyze LSST data).

When I received the Early Career Award, I was co-lead of the weak lensing working group within the LSST Dark Energy Science Collaboration (DESC). After three years in that role, I became the collaboration’s Analysis Coordinator, providing oversight to all science working groups for the following four years. Next, I served a two-year term as collaboration spokesperson. After my spokesperson term, I have remained an active member of the collaboration’s scientific effort and hold several service roles

The Early Career Award was crucial in enabling me to dedicate my skills and time to DESC during a critical time in the collaboration’s development.


Rachel Mandelbaum is a professor in the Department of Physics at Carnegie Mellon University.


The Early Career Research Program provides financial support that is foundational to early career investigators, enabling them to define and direct independent research in areas important to DOE missions. The development of outstanding scientists and research leaders is of paramount importance to the Department of Energy Office of Science. By investing in the next generation of researchers, the Office of Science champions lifelong careers in discovery science.

For more information, please go to the Early Career Research Program.


Title: Optimal Cosmological Measurements with Weak Gravitational Lensing


Weak gravitational lensing is the most direct way to observe distributions of dark matter in the universe. Weak gravitational lensing can also be used to study dark energy, which causes accelerated expansion of the universe and a slowing of the growth of large‐scale structures (such as galaxy clusters) containing dark matter. Several large astronomical imaging surveys have been planned to measure weak gravitational lensing more precisely than ever before, eventually culminating in the Large Synoptic Survey Telescope (LSST). These imaging surveys gain in power when combined with spectroscopic surveys like the ongoing Baryon Oscillation Spectroscopic Survey (BOSS). The purpose of this project is to carry out measurements of weak gravitational lensing and then combine these results with other cosmological observations to identify optimal ways of constraining cosmological parameters and the nature of dark energy. The results will ensure that next‐generation dark energy experiments realize their full potential.


R Mandelbaum, "Weak Lensing for Precision Cosmology." Ann. Rev. Astron. Astrophys. 56:393; (2018). [DOI: 10.1146/annurev-astro-081817-051928]

C Chang, et al., "A unified analysis of four cosmic shear surveys." Mon. Not. R. Astr. Soc. 482:3696; (2019). [DOI: 10.1093/mnras/sty2902]

LSST Dark Energy Science Collaboration (LSST DESC) et al., "The LSST DESC DC2 Simulated Sky Survey." Astrophys. J. Supp. 253(1):31 (2021). [DOI: 10.3847/1538-4365/abd62c]


DOE Explains… offers straightforward explanations of key words and concepts in fundamental science. It also describes how these concepts apply to the work that the Department of Energy’s Office of Science conducts as it helps the United States excel in research across the scientific spectrum. For more information on dark energy, on cosmology, and on DOE’s research in this area, please go to “DOE Explains…Cosmic Acceleration and Dark Energy and “DOE Explains…Cosmology." 

Additional profiles of the Early Career Research Program award recipients can be found at Early Career Program highlights page.  

The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website.


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