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News — STONY BROOK, NY, March 18, 2025 – Research by the  (ACT) collaboration has produced new images that are the clearest yet of the universe’s infancy – the earliest cosmic time accessible; the images are of the cosmic microwave background (CMB) radiation that was visible only 380,000 years after the Big Bang.

The international collaboration of scientists includes astrophysicist , PhD, and her group in the Department of Physics and Astronomy in the College of Arts and Sciences at Stony Brook University. The Stony Brook team has played an essential role within the collaboration in analyzing the CMB, the afterglow light from the Big Bang.

The new images measure light that traveled for more than 13 billion years to reach the ACT high in the Chilean Andes and reveal the universe at about 380,000 years old, which the team considers the equivalent of hours-old baby pictures of the cosmos, now in about middle-age.

“We are seeing the first steps towards making the earliest stars and galaxies,” says Suzanne Staggs, Director of ACT and Henry deWolf Smyth Professor of Physics at Princeton University. “And we’re not just seeing light and dark, we’re seeing the polarization of light in high resolution. That is a defining factor distinguishing ACT from  and other, earlier telescopes.”

The research team says these results confirm a simple model of the universe and have ruled out most competing alternatives. The new images of the CMB add higher definition to those observed a decade ago by the Planck space-based telescope. Their findings will be presented at the American Physical Society Annual Meeting on March 19.

In the first several hundred thousand years after the Big Bang, the primordial plasma was so hot that light could not propagate freely, making the universe effectively opaque. The CMB represents the first stage in the universe’s history that we can see – effectively, the universe’s baby picture.  

The images give a remarkably clear view of very, very subtle variations in the density and velocity of the gases. The polarization image also reveals the detailed movement of the hydrogen and helium gas in the cosmic infancy.

“With these images, we have achieved a sensitivity over half the sky that surpasses previous ‘baby pictures’ of the universe,” says Sehgal, Associate Professor in the Department of Physics and Astronomy, and leader of an international team proposing a next-generation CMB experiment called .

“The sensitivity is particularly outstanding on small scales and in measurements of the polarization of CMB light. In addition, other data sets have claimed tensions with the Standard Model of Cosmology; however, with this work we have tested the standard model in different ways and find no evidence of any cracks,” she adds, emphasizing that the ACT’s polarization data is a key new aspect of the work analyzing the infancy of the universe.

Answers to Previous Questions

These new detailed images of the newborn universe are revealing answers to longstanding scientific questions about the universe’s origins.

“By looking back to that time, when things were much simpler, we can piece together the story of how our universe evolved to the rich and complex place we find ourselves in today,” says Jo Dunkley, Joseph Henry Professor of Physics and Astrophysical Sciences at Princeton University and the ACT analysis leader.

ACT’s new measurements have also refined estimates for the age of the universe and how fast it is growing today. The infall of matter in the early universe sent out sound waves through space, like ripples spreading out in circles on a pond.

“Before, we got to see where things were, and now we also see how they’re moving,” explains Staggs. “Like using tides to infer the presence of the moon, the movement tracked by the light’s polarization tells us how strong the pull of gravity was in different parts of space.”

In recent years, cosmologists have , the rate at which space is expanding today. Measurements derived from the CMB have consistently shown an expansion rate of 67–68 kilometers per second per megaparsec, while measurements derived from the movement of nearby galaxies indicate a Hubble constant as high as 73–74 km/s/Mpc.

Using their newly released data, the ACT team confirmed the lower value for the Hubble constant, and with increased precision.

The Stony Brook team has been involved with the CMB analysis for more than 10 years. Led by Sehgal, the researchers include current and former Department of Physics and Astronomy graduate students Mathew Madhavacheril, Dongwon Han, and Amanda MacInnis.

ACT completed its observations in 2022, and attention is now turning to the new, more capable, Simons Observatory at the same location in Chile. Stony Brook is an institutional partner in the Simons Observatory, which has .

The new ACT data are shared publicly on NASA’s LAMBDA archive. The pre-peer review articles highlighted in this release are available on the  and will appear on the open access arXiv.org.

Sehgal’s research and group have been funded by the U.S. National Science Foundation (NSF) and the U.S. Department of Energy (DOE). The ACT project and this research was supported by NSF awards (AST-0408698, AST-0965625 and AST-1440226 for the ACT project, as well as awards PHY-0355328, PHY-0855887 and PHY-1214379), Princeton University, the University of Pennsylvania, and a Canada Foundation for Innovation award. The project is led by Princeton University and the University of Pennsylvania, with 160 collaborators at 65 institutions.

Tour of the new Atacama Cosmology Telescope data, adding high definition to earlier images from the Planck satellite
Credit: ACT Collaboration; ESA/Planck Collaboration