Scientists capture 'baby pictures' of the very early universe
A team of astronomers has unveiled the most detailed images yet of the universe’s infancy, capturing light that traveled for more than 13 billion years before reaching Earth.
These observations, made from a telescope high in the Chilean Andes, provide an unprecedented glimpse of the cosmos when it was just 380,000 years old – equivalent to baby pictures of a universe that has since grown into its middle age.
“We are seeing the first steps towards making the earliest stars and galaxies,” said Suzanne Staggs, director of the Atacama Cosmology Telescope (ACT) and a 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.”
Viewing the universe with greater clarity
The newly released images capture the cosmic microwave background (CMB), the faint radiation left over from the Big Bang.
While the Planck space telescope previously mapped this radiation more than a decade ago, ACT’s observations provide significantly greater clarity.
“ACT has five times the resolution of Planck, and greater sensitivity,” said Sigurd Naess, a researcher at the University of Oslo and lead author of one of the papers detailing the findings. “This means the faint polarization signal is now directly visible.”
Polarization patterns in the CMB provide insight into the motion of hydrogen and helium gases in the early universe.
“Before, we got to see where things were, and now we also see how they’re moving,” Staggs explained. “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.”
The results reinforce the standard model of cosmology, while eliminating many competing alternatives.
Looking back at the baby universe
For the first few hundred thousand years after the Big Bang, the universe was filled with a dense, hot plasma that prevented light from traveling freely.
Only after the universe cooled enough for atoms to form did photons begin streaming through space, creating the CMB – essentially, the first visible record of the cosmos.
The new images provide an exceptionally detailed view of minute variations in the density and motion of primordial gases.
“There are other contemporary telescopes measuring the polarization with low noise, but none of them cover as much of the sky as ACT does,” Naess noted.
The variations seen in the CMB – regions of slightly denser or less dense hydrogen and helium – represent the early “seeds” of structure in the universe.
Over millions and billions of years, gravity drew these denser regions together, forming the first stars and galaxies.
“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,” said Jo Dunkley, a professor of physics and astrophysical sciences at Princeton University and leader of ACT’s data analysis.
Measuring the mass of the universe
The research also provided a new, precise measurement of the total mass of the observable universe.
“We’ve measured more precisely that the observable universe extends almost 50 billion light years in all directions from us, and contains as much mass as 1,900 ‘zetta-suns,’ or almost two trillion trillion Suns,” said Erminia Calabrese, a professor of astrophysics at Cardiff University and a lead author on one of the papers.
Composition of the universe
The composition of the universe, as determined by ACT, aligns well with existing cosmological models.
The total mass of the universe is divided into several components. Normal matter, which includes planets, stars, and galaxies, has a mass equivalent to 100 zetta-suns.
Dark matter, a mysterious and invisible substance that shapes galaxy formation, accounts for 500 zetta-suns.
Dark energy, the force responsible for the universe’s accelerated expansion, has a mass equivalent to 1,300 zetta-suns. Finally, neutrinos, tiny and nearly massless particles, contribute at most 4 zetta-suns.
Hydrogen and helium
The findings also confirm that roughly 75% of normal matter in the universe is hydrogen, while the remaining 25% is helium.
“Almost all of the helium in the universe was produced in the first three minutes of cosmic time,” said Thibaut Louis, a researcher at the University Paris-Saclay and one of the study’s lead authors.
The heavier elements, including those that make up human bodies – carbon, oxygen, nitrogen, and even trace amounts of gold – formed much later inside stars.
Refining the age of the universe
ACT’s measurements have also refined estimates of the universe’s age and its current rate of expansion. The early universe’s density fluctuations sent sound waves rippling through space, much like waves spreading across a pond.
“A younger universe would have had to expand more quickly to reach its current size, and the images we measure would appear to be reaching us from closer by,” explained Mark Devlin, a professor of astronomy at the University of Pennsylvania and ACT’s deputy director.
“The apparent extent of ripples in the images would be larger in that case, in the same way that a ruler held closer to your face appears larger than one held at arm’s length.”
Using this method, the research confirms that the universe is 13.8 billion years old, with an uncertainty of just 0.1 percent.
Addressing the Hubble constant debate
One of the major ongoing questions in cosmology is the discrepancy in measurements of the Hubble constant, which describes the rate at which the universe is expanding today.
Observations from the CMB have consistently suggested an expansion rate of 67 to 68 km/s per Megaparsec, while measurements based on the movement of nearby galaxies suggest a higher value of 73 to 74 km/s/Mpc.
With its new data, the ACT team has determined a Hubble constant consistent with previous CMB-based estimates.
“We took this entirely new measurement of the sky, giving us an independent check of the cosmological model, and our results show that it holds up,” said Adriaan Duivenvoorden, a research fellow at the Max Planck Institute for Astrophysics and lead author on one of the papers.
Extraordinarily precise model
The researchers also investigated alternative cosmological models that might explain the discrepancy.
“We wanted to see if we could find a cosmological model that matched our data and also predicted a faster expansion rate,” said Colin Hill, an assistant professor at Columbia University.
The team explored modifications to dark matter, changes to neutrino behavior, and even a period of early accelerated expansion.
“We have used the CMB as a detector for new particles or fields in the early universe, exploring previously uncharted terrain,” Hill said. “The ACT data show no evidence of such new signals. With our new results, the standard model of cosmology has passed an extraordinarily precise test.”
“It was slightly surprising to us that we didn’t find even partial evidence to support the higher value. There were a few areas where we thought we might see evidence for explanations of the tension, and they just weren’t there in the data.”
Peering deeper into the baby universe
ACT’s observations required a five-year exposure using advanced detectors designed to measure millimeter-wavelength light.
Though ACT concluded its observations in 2022, scientists are now preparing for the next-generation Simons Observatory, which will be even more powerful and operate from the same location in Chile.
By peering deeper into the universe’s infancy, ACT has provided critical insights into the cosmos’ evolution, helping scientists refine our understanding of its past, present, and future.
The research was presented at the American Physical Society annual conference.
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