New images from the Atacama Cosmology Telescope (ACT) reveal the Universe when it was about 380,000 years old.
An image of the CMB radiation from the Atacama Cosmology Telescope; orange and blue represent more or less intense radiation. Image credit: ACT Collaboration.
The new ACT pictures of the so-called Cosmic Microwave Background (CMB) add higher definition to those observed more than a decade ago by ESA’s Planck space-based telescope.
“We are seeing the first steps towards making the earliest stars and galaxies,” said Princeton University Professor Suzanne Staggs, director of ACT.
“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.”
“ACT has five times the resolution of Planck, and greater sensitivity,” said Dr. Sigurd Naess, a researcher at the University of Oslo.
“This means the faint polarization signal is now directly visible.”
The polarization image reveals the detailed movement of the hydrogen and helium gas in the cosmic infancy.
“Before, we got to see where things were, and now we also see how they’re moving,” Professor Staggs said.
“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 new results confirm a simple model of the Universe and have ruled out a majority of competing alternatives.”
In the first several hundred thousand years after the Big Bang, the primordial plasma that filled the Universe was so hot that light couldn’t 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 new ACT images give a remarkably clear view of very, very subtle variations in the density and velocity of the gases that filled the young Universe.
“There are other contemporary telescopes measuring the polarization with low noise, but none of them cover as much of the sky as ACT does,” Dr. Naess said.
“What look like hazy clouds in the light’s intensity are more and less dense regions in a sea of hydrogen and helium — hills and valleys that extend millions of light years across.”
“Over the following millions to billions of years, gravity pulled the denser regions of gas inwards to build stars and galaxies.”
These detailed images of the newborn Universe are helping scientists to answer longstanding 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, ” said Princeton University Professor Jo Dunkley, ACT analysis leader.
“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 2 trillion trillion Suns,” added University of Cardiff’s Professor Erminia Calabrese.
“Of those 1,900 zetta-suns, the mass of normal matter — the kind we can see and measure — makes up only 100.”
“Another 500 zetta-Suns of mass are mysterious dark matter, and the equivalent of 1,300 are the dominating vacuum energy (also called dark energy) of empty space.”
Tiny neutrino particles make up at most four zetta-suns of mass. Of the normal matter, three-quarters of the mass is hydrogen, and a quarter helium.
“Almost all of the helium in the Universe was produced in the first three minutes of cosmic time,” said Dr. Thibaut Louis, a researcher at the University Paris-Saclay and CNRS.
“Our new measurements of its abundance agree very well with theoretical models and with observations in galaxies.”
“The elements that we humans are made of — mostly carbon, with oxygen and nitrogen and iron and even traces of gold — were formed later in stars and are just a sprinkling on top of this cosmic stew.”
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.
“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,” said University of Pennsylvania’s Professor Mark Devlin, 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.”
“The new data confirm that the age of the Universe is 13.8 billion years, with an uncertainty of only 0.1%.”
In recent years, cosmologists have disagreed about the Hubble constant, the rate at which space is expanding today.
Measurements derived from the CMB have consistently shown an expansion rate of 67 to 68 km per second per megaparsec, while measurements derived from the movement of nearby galaxies indicate a Hubble constant as high as 73 to 74 km per second per megaparsec.
Using their newly released data, the ACT team has measured the Hubble constant with increased precision.
Their measurement matches previous CMB-derived 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 Dr. Adriaan Duivenvoorden, a researcher at the Max Planck Institute for Astrophysics.
A major goal of the work was to investigate alternative models for the Universe that would explain the disagreement.
“We wanted to see if we could find a cosmological model that matched our data and also predicted a faster expansion rate,” said Dr. Colin Hill, a researcher at Columbia University.
“Alternates include changing the way neutrinos and the invisible dark matter behave, adding a period of accelerated expansion in the early Universe or changing fundamental constants of nature.”
“We have used the CMB as a detector for new particles or fields in the early Universe, exploring previously uncharted terrain,” Dr. 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,” Professor Staggs said.
“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.”
