Claire Lamman

Imagine the structure of our universe as a cosmic-sized spider web. Galaxies cluster along the web’s strands and nodes. Since the big bang, a mysterious force called dark energy has been stretching the overall geometry of the web very quickly. At the same time, however, gravitational forces operating on the galaxies are pulling matter closer together, albeit at a slower rate than we would expect due to the counter effect of dark energy. The result is a bit of a paradox, according to 2024 Harvard Horizons Scholar and astronomy PhD student Claire Lamman.  

“The web of the universe is becoming more and more defined,” she says. “The nodes are becoming denser, even as the size of the web is growing.”  

Lamman is part of a team of astrophysicists using data from the Dark Energy Spectroscopic Instrument (DESI) to map as many as 50 million galaxies. Her Harvard Horizons project, “Untangling the Cosmic Web,” describes Lamman’s distinctive contribution to this effort—gauging the “intrinsic alignment” of galaxies to better understand the universe and how it evolves.  

DESI’s criteria for which galaxies it chooses to capture depends on how bright the target galaxy is. But Lamman says the brightness of a galaxy is influenced by its orientation relative to the Earth.  

“Big galaxies tend to take the shape of ovals, and they tend to point toward the denser parts of the cosmic web of the universe,” she says. “Thus, galaxies in the troughs, where there is less dark matter, tend to point toward the strands of the web. And galaxies in the strands tend to be aligned with the strands.” Because DESI’s sample bias privileges galaxies pointed toward Earth, “some troughs look ‘troughier’ and some peaks look ‘peakier’ than they should in reality.”  

This sample bias makes data less representative of the universe as a whole. Given the cosmic scale of the research, even the tiniest errors can compound and skew astronomers’ understanding of the universe.  

That’s where Lamman’s research comes in. She studies the true shapes and orientations of the galaxies—their intrinsic alignments. Spectroscopy provides Lamman data on millions of galaxies, which allows her to make statistical inferences about their orientation in ways that were not possible before DESI. Based on that information, Lamman writes in her Harvard Horizons proposal that “we observe more clustering along the line-of-sight than in the plane of the sky.” She predicts that these alignments will bias DESI’s measurements by nearly 1 percent, a problem for a precision-cosmology survey that is designed to make measurements with sub-percent precision.  

“One percent is a tiny fraction of our overall measurement, but a large portion of our error budget,” she says. “We need my corrections to distinguish between certain models of dark energy.” 

In the years ahead, Lamman hopes to inspire others to pursue the big questions that are the inspiration for her research. While she knows that the layperson may not immediately understand the significance of her work, she says the impulse that lies behind it is, no pun intended, universal.  

“I’m searching for answers about very fundamental questions,” she says. “What is the universe made of? And how does it change? The answers leave imprints in the galaxies we observe, which are uniquely traced by intrinsic alignments.”