Imagine a baby that is born and, just a few hours later, they take your first photograph. That image is the equivalent in a human life that the universe has obtained from the universe Atacama Cosmological Telescope (ACT)in the Chilean Andes. The telescope has captured the most clear images to the cosmos childhood date, when he was just 380,000 years old. Does it still seem a lot? He has currently turned 13.8 billion years.
“We are seeing the first steps towards the formation of the first stars and galaxies,” says Suzanne Staggs, director of the Act and Professor of Physics at Princeton University. «And we not only see light and darkness, but the polarization of light in high resolution. This is a decisive factor that distinguishes the act from Planck and other previous telescopes, ”he adds.
The new images of this background radiation, known as Cosmic Microwave Fund (CMB), add greater definition to those observed more than a decade ago by the Planck Space Telescope. “ACT has five times the Planck resolution and greater sensitivity,” says Sigurd Naess, a researcher at the University of Oslo and the main author of one of the various articles related to the project. “This means that the faint polarization signal is now directly visible.”
The polarization image reveals the detailed movement of hydrogen and helium in its cosmic childhood. “Before, we could see where things were, and now we see how they move,” says Staggs. “As if the tides were used to infer the presence of the moon, the movement recorded by the polarization of light indicates the intensity of gravitational attraction in different parts of the space.”
The new results confirm a simple model of the universe and discard most of the alternatives, says the research team. The work has not yet been reviewed by pairs, but researchers will present their results at the annual conference of the American Society of Physics on March 19.
Cosmic childhood
During the first hundreds of thousands of years after the Big Bang, the original plasma that filled the universe was so hot that the light could not spread freely, which made the universe practically opaque. The CMB represents the first visible stage in the history of the universe; In essence, the initial image of the universe.
The new images offer an extraordinarily clear vision of the subtle variations in the density and speed of the gases that filled the young universe. What seem diffuse clouds to the intensity of light are more or less dense regions in a sea of hydrogen and helium: hills and valleys that extend millions of light years of diameter. During the following millions to billions of years, gravity attracted the densest gas regions to the interior to form stars and galaxies.
These detailed images of the newborn universe are helping scientists answer questions about their origin. “Remembering that time, when things were much simpler, we can reconstruct the history of how our universe evolved until reaching the rich and complex world in which we are today,” says Jo Dunkley, professor of Physics and Astrophysical Sciences at Princeton University and leader of Act’s analysis.
“We have measured more accurately than the observable universe extends almost 50,000 million light years in all directions from us and contains as much mass as 1900 ‘Zetta-Sols’, or almost 2 billion billion soles,” says Erminia Calabrese, a professor of astrophysics at the University of Cardiff and the main author of one of the new articles. Of those 1900 Zetta-Sol, the mass of normal matter (the one we can see and measure) represents only 100. Another 500 Zetta-Sol of mass are mysterious dark matter, and the equivalent of 1,300 are the dominant vacuum energy (also called dark energy) of the empty space.
The tiny neutrin particles constitute, at most, four mass zeta soles. Of normal matter, three quarters of the dough are hydrogen and a quarter, helium. “Almost all the Helium of the Universe occurred in the first three minutes of cosmic time,” says Thibaut Louis, a CNRS researcher at the IJCLAB of the Paris-Saclay University and one of the main authors of the new articles. “Our new measurements of their abundance agree very well with the theoretical models and with galaxies observations.” The elements of which we are made – mainly carbon, with oxygen, nitrogen, iron and even traces of gold – were subsequently formed in the stars and are just a pinch of this cosmic mixture.
The new Act measurements have also perfected estimates of the age of the universe and its current growth rate. The fall of matter in the primitive universe issued sound waves through space, as waves that extend in circles in a pond.
“A youngest universe would have had to expand more quickly to achieve its current size, and the images we measure would seem to get closer to us,” explains Mark Devlin, a professor of Astronomy Reese W. Flower at the University of Pennsylvania and deputy director of the ACT. “The apparent extension of the undulations in the images would be greater in that case, in the same way that a sustained rule near the face seems larger than a sustained with an extended arm.” The new data confirms that the age of the universe is 13.8 billion years, with an uncertainty of only 0.1 %.
Hubble tension
In recent years, cosmologists have disagreed on Hubble constant, the speed at which space expands today. The measurements derived from the WBC have consistently shown an expansion rate of 67 to 68 kilometers per second by Megapársec, while the measurements derived from the movement of nearby galaxies indicate a hubble constant of up to 73 to 74 km/s/mpc. Using its newly published data, the ACT team has measured the Hubble constant with greater precision. Its measurement coincides with the previous estimates derived from the CMB. “We take this completely new measurement of the sky, which provides us with an independent verification of the cosmological model, and our results show that it is sustained,” says Adriaan Duiveenvoorden, researcher at the Max Planck Institute of Astrophysics and principal author of one of the new articles.
A main objective of the work was to investigate alternative models of the universe that explained this discrepancy. “We wanted to see if we could find a cosmological model that coincided with our data and that also predicted a faster expansion rate,” says Colin Hill, an attached professor at Columbia University and one of the main authors of the new articles. Alternatives include modifying the behavior of neutrinos and invisible dark matter, adding an accelerated expansion period in the primitive universe or modifying the fundamental constants of nature.
“We have used the WBC as a detector of new particles or fields in the primitive universe, exploring previously unexplored land,” says Hill. «ACT data does not show evidence of these new signals. With our new results, the standard cosmology model has exceeded an extraordinary precision test ».
When studying the sky, Act has also detected the light emitted by other objects in space. “We can go back in time through cosmic history,” says Dunkley, “from our own Milky Way, through distant galaxies that house vast black holes and huge clusters of galaxies, until reaching that time of his childhood.”
The ACT completed its observations in 2022, and now the attention focuses on the new Simons Observatory, of greater capacity, located in the same place in Chile.
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