An international team of researchers including Yale’s Indian American professor Priyamvada Natarajan, say next year’s launch of NASA’s Nancy Grace Roman Space Telescope will help them take a closer look at dark matter.
It may transform their ability to find what are known as gravitational lenses — pairs of galaxies that can act as cosmic magnifying glasses to peer deeper into the universe, according to a university press release.
Dark matter, which is thought to constitute the majority of all matter, does not reflect, absorb, or emit light. But it does have mass, which means it generates gravity and can cause gravitational lensing.
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Dark matter particles are believed to have originated in the early universe but have yet to be detected — hence, their true nature remains elusive. One of the most clear-cut astronomical signatures that would reveal dark matter is the amount of “clumping,” or substructure, found on small scales.
In a new study published in The Astrophysical Journal, the international research team estimated that “Roman” may be able to find more than 160,000 gravitational lenses, including about 500 that are suitable for studying the structure of dark matter.
“These findings underscore the significant potential of Roman in advancing strong lensing studies and enhancing our understanding of dark matter substructure through high-resolution observations,” said Natarajan, the Joseph S. and Sophia S. Fruton Professor and Chair of Astronomy and professor of physics in Yale’s Faculty of Arts and Sciences (FAS).
Natarajan, the main theorist and co-author of the new study, is also director of Yale’s Franke Program in Science and the Humanities.
When the gravity of a foreground galaxy bends the path of a background galaxy’s light, its light is routed onto multiple paths. Roman’s camera, known as its Wide Field Instrument, will allow researchers to accurately determine the bending of the background galaxies’ light by as little as 50 milliarcseconds, which is like measuring the diameter of a human hair from the distance of more than two and a half football fields.
The amount of gravitational lensing that the background light experiences depends on the intervening mass. Less massive clumps of dark matter cause smaller distortions.
As a result, if researchers are able to measure tinier amounts of bending, they can detect and characterize smaller, less massive dark matter structures — the types of structures that gradually merged over time to build up the galaxies we see today.
“The strong lensing we’ll be able to study thanks to Roman should provide a way for us to test the Lambda Cold Dark Matter cosmological model — our current standard model for understanding the evolution of the universe — at sub-galactic scales,” Natarajan said. “It would be a huge advance for the field.”
Before Roman launches, the team will also search for more candidates in observations from ESA’s (the European Space Agency’s) Euclid mission and the upcoming ground-based Vera C. Rubin Observatory in Chile, which will begin its full-scale operations in a few weeks.
Once Roman’s images are in hand, the researchers will combine them with complementary visible light images from Euclid, Rubin, and Hubble to maximize what’s known about these galaxies.
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Bryce Wedig, a graduate student at Washington University in St. Louis, led the new study. The principal investigator was Tansu Daylan, an assistant professor at Washington University in St. Louis.
Natarajan joined the Yale faculty in 2000. Among her many honors, she is an elected fellow of the American Academy of Arts and Sciences, the AAS, the American Physical Society, and the American Association for the Advancement of Science.
She also is the recipient of Guggenheim and Radcliffe fellowships and the Liberty Science Center’s Genius Award. In 2024, she was included in Time Magazine’s list of the 100 most influential people in the world.