This is part of a new image that shows the vibration directions, or polarization, of the radiation. The zoom-in on the right is 10 degrees high. Polarized light vibrates in a particular direction; blue shows where the surrounding light’s vibration directions are angled towards it, like spokes on a bicycle; orange shows places where the vibration directions circle around it. This new information reveals the motion of the ancient gases in the universe when it was less than half a million years old, pulled by the force of gravity in the first step toward forming galaxies. The red band comes from our closer-by Milky Way.
This is part of a new image that shows the vibration directions, or polarization, of the radiation. The zoom-in on the right is 10 degrees high. Polarized light vibrates in a particular direction; blue shows where the surrounding light’s vibration directions are angled towards it, like spokes on a bicycle; orange shows places where the vibration directions circle around it. This new information reveals the motion of the ancient gases in the universe when it was less than half a million years old, pulled by the force of gravity in the first step toward forming galaxies. The red band comes from our closer-by Milky Way.
This is part of a new image that shows the vibration directions, or polarization, of the radiation. The zoom-in on the right is 10 degrees high. Polarized light vibrates in a particular direction; blue shows where the surrounding light’s vibration directions are angled towards it, like spokes on a bicycle; orange shows places where the vibration directions circle around it. This new information reveals the motion of the ancient gases in the universe when it was less than half a million years old, pulled by the force of gravity in the first step toward forming galaxies. The red band comes from our closer-by Milky Way.
For the first time, scientists can see not just the light and dark of our infant universe, but also how that primordial gas was moving. An international collaboration of researchers has produced the most detailed images yet of what our cosmos looked like a mere 380,000 years after the Big Bang – equivalent to baby pictures of a now middle-aged universe.
The images, captured by the Atacama Cosmology Telescope (ACT) high in the Chilean Andes, reveal light that traveled more than 13 billion years to reach Earth. They represent the earliest cosmic time that can be observed by humans.
“We are seeing the first steps towards making the earliest stars and galaxies,” said 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 Planck and other, earlier telescopes.”
This cosmic baby album provides insights that confirm the Standard Model of Cosmology while ruling out competing alternatives. The findings, which will be presented at the American Physical Society Annual Meeting on March 19, add significant definition to observations made a decade ago by the Planck space-based telescope.
During the universe’s first several hundred thousand years, the primordial plasma was so hot that light couldn’t move freely, rendering the cosmos effectively opaque. What we now see as the cosmic microwave background (CMB) radiation represents the first moment in cosmic history when light could travel unimpeded – essentially when the universe became transparent.
Scientists explain that these new images reveal remarkably subtle variations in the density and velocity of hydrogen and helium gases present during cosmic infancy. The polarization data is particularly valuable as it shows detailed movement of these gases.
Neelima Sehgal, Associate Professor in the Department of Physics and Astronomy at Stony Brook University and a key member of the ACT collaboration, emphasized the significance of these observations.
“With these images, we have achieved a sensitivity over half the sky that surpasses previous ‘baby pictures’ of the universe,” said Sehgal, who also leads an international team proposing a next-generation CMB experiment called CMB-HD.
“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 added.
The Stony Brook team’s contribution has been essential to the collaboration’s success. Led by Sehgal, researchers including graduate students Mathew Madhavacheril, Dongwon Han, and Amanda MacInnis have been analyzing the CMB for more than a decade.
Settling Cosmic Disputes
Beyond providing breathtaking views of the newborn universe, these observations are helping resolve longstanding scientific debates about cosmic origins and evolution.
“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,” explained Jo Dunkley, Joseph Henry Professor of Physics and Astrophysical Sciences at Princeton University and the ACT analysis leader.
One persistent disagreement among cosmologists concerns the Hubble constant – the rate at which space is expanding today. CMB-derived measurements have consistently indicated an expansion rate of 67–68 kilometers per second per megaparsec, while measurements based on nearby galaxy movement suggest a higher rate of 73–74 km/s/Mpc.
The ACT team’s newly released data confirms the lower value with increased precision, though this is unlikely to fully resolve the debate.
The telescope’s ability to detect polarization in the CMB light has proven particularly valuable. Staggs explained the significance using an analogy: “Before, we got to see where things were, and now we also see how they’re moving. 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.”
This polarization data reveals the sound waves that rippled through the early universe as matter fell inward under gravity’s influence – similar to ripples spreading in circles across a pond.
Looking Forward
While ACT completed its observations in 2022, the research continues. Attention is now turning to the new, more capable Simons Observatory at the same location in Chile. Stony Brook University is an institutional partner in this new observatory, which has recently achieved “first light” – capturing its initial observations.
The collaboration’s commitment to open science is evident in their approach to data sharing. The new ACT data are publicly available on NASA’s LAMBDA archive, with pre-peer review articles accessible on the ACT website and the open access platform arXiv.org.
This research was supported by numerous grants from the U.S. National Science Foundation, the U.S. Department of Energy, Princeton University, the University of Pennsylvania, and a Canada Foundation for Innovation award. The ACT project involves 160 collaborators from 65 institutions and is led by Princeton University and the University of Pennsylvania.
As researchers continue analyzing these cosmic baby photos, they expect to uncover further clues about how our universe evolved from a nearly uniform gas into the complex cosmos we inhabit today – a universe filled with galaxies, stars, planets, and ultimately, life itself.
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