2024-07-21 06:00:09
The first telescopes at the Simons Observatory in Chile have begun taking data, marking the scientific start of a 10-year project that aims to make the most precise measurement ever made of the radiation of cosmic microwave background.
The aim is to try to detect in these first glimmers of the cosmos the tiny traces of gravitational waves that would have been generated by a phase of inflation of the primordial Universe. A project in which two laboratories of IN2P3, APC and IJCLab, are participating.
The Simons Observatory, which has just completed its main construction phase on the heights of the Atacama Desert in Chile, will be able to begin its data collection, which should lead to the most precise measurements ever made of the oldest light in the Universe. This latter, known as the Cosmic Microwave Background, was emitted approximately 380,000 years after the Big Bang and holds the secrets of the birth of the cosmos.
Indeed, scientists predict that a period of rapid expansion of the Universe in its earliest moments, called inflation, may have generated gravitational waves in the fabric of spacetime. These waves affect the polarization properties of the cosmic microwave background light, imprinting it with a particular pattern, which cosmologists call “polarization B modes.”
“Their discovery would provide an unprecedented window into how the universe was born and offer confirmation of the theory of inflation,” said Mark Devlin, co-director of the University of Pennsylvania observatory. “The amplitude of the primordial B modes will tell us about the state of the universe in the first moments after its birth.”
“The question of the origin of the universe has always fascinated humans,” said Brian Keating, principal investigator at the University of California, San Diego, observatory. “With Simons Observatory, we are on the verge of discovering answers rooted not in mere speculation, but in the most precise data ever collected by the world’s most advanced telescopes.”
“We are taking research into the early universe to a new level,” says Suzanne Staggs, co-director of the Simons Observatory at Princeton University. “The sensitivity of our instruments opens up new perspectives for the field.”
The quest
One of the main scientific goals of the Simons Observatory is to help elucidate what happened in the first decillionth of a second after the Big Bang (that’s a trillionth of a trillionth of a billionth of a second). In that brief moment, scientists believe the universe expanded by a factor of 100 trillion trillion. That would be comparable to a bacterium growing to the size of a galaxy.
To take advantage of ideal observing conditions, the Simons Observatory is located on Mount Toco at an altitude of nearly 5,200 m in the Atacama Desert in Chile. The image shows the three 40-centimeter aperture telescopes (SAT), surrounded by a screen protecting them from terrestrial emissions, and in the foreground the structure of the 6-meter aperture telescope (LAT) currently being installed.
Image: Gabriele Coppi, Rolando Dunner, Ederico Nati, Matias Rojas
Quantum fluctuations in the early Universe are thought to have generated the first inhomogeneities in the cosmos that later evolved to create the distribution of matter we observe in the modern Universe. These same fluctuations also generated ripples in spacetime called primordial gravitational waves.
Although this inflationary period was a crucial moment in the history of the Universe, we cannot observe it directly. The early Universe was too hot and dense for light to propagate freely. It was only after 380,000 years of evolution, and the cooling of the plasma that makes up the early Universe, that light could begin to move unhindered. This is the cosmic microwave background that we observe today.
Like light passing through a pair of polarized sunglasses, light from the cosmic microwave background can have a preferred orientation, or “polarization.” Gravitational waves from inflation would have left subtle patterns called B-modes in the polarization of the cosmic microwave background. Detecting these B-modes would provide unprecedented insights into the early universe.
“We’re on the trail of a signal generated in the first billionth of a trillionth of a trillionth of a second after the Big Bang,” says Arthur Kosowsky, a spokesperson for the collaboration at the University of Pittsburgh’s Simons Observatory. “No one knows if this signal is still big enough to see today. Seeing it would be like winning the physics lottery — the scientific impact would be immense.”
Mapping the cosmic microwave background
The Simons Observatory comprises three 0.4-meter Small Aperture Telescopes (SATs) and a 6-meter Large Aperture Telescope (LAT), which together will achieve unprecedented sensitivity for measuring the polarization of the cosmic microwave background. Since April 2024, two of the SATs have been calibrated and are now in theobservationthe third SAT should be operational in the coming months and the LAT at the beginning of next year.
Image of the planet Jupiter with the Simons Observatory detectors. The apparent size of the planet reflects the resolution of the telescope’s optics. Jupiter scans are among the first observations and were used to calibrate the observatory’s instruments.
Image: The Simons Observatory collaboration
The Simons Observatory’s size and innovative use of new technologies allow it to create detailed maps of the cosmic microwave background at a rate many times faster than previous generations of telescopes. Together, the observatory’s four telescopes will have 60,000 detectors collecting data, more than all other projects combined.
The observatory’s superconducting detectors operate at temperatures 0.1 degrees above absolute zero, using cooling technology similar to that used in quantum computers. “I’m impressed that our instruments are working so well,” says Jeff McMahon, a founding member of the University of Chicago’s Simons Observatory. “I’m even more excited about the science these telescopes are starting to produce.”
The three SATs will together survey an area covering 20% ​​of the southern hemisphere sky, while the LAT will map 40% of the sky at a finer resolution. By combining the sensitivity of the telescopes with innovative data analysis techniques, the Simons Observatory team maximizes its chances of spotting the B-modes they are looking for.
The future of the observatory
After about four years of operation, the observatory will benefit from the addition of 30,000 additional detectors thanks to a grant from the National Science Foundation (United States). The total observation period of the telescopes will be about 10 years.
“Ten years may seem like a long time, but if you use the capabilities of current telescopes, it would take 60 years to reach our sensitivity,” says Mark Devlin. Additional telescopes funded by Japan and the UK are also due to come online in 2026, doubling the number of SATs.
French participation in the observatory
The IN2P3 teams are taking part in the Simons project, with the participation of the APC and IJCLab laboratories.
“Detecting polarization B modes is like finding a needle in a haystack,” says Josquin Errard, a European Research Council (ERC) grant recipient and co-leader of the measurement of primordial B modes within the collaboration. “Observations of the cosmic microwave background are indeed affected by all sorts of emissions of astrophysical and environmental origin that contaminate the signal, in particular emissions from our own galaxy: the Milky Way. We are working on developing new data analysis methods that will make it possible to separate the different contributions.”
In parallel, a possible French instrumental contribution to the observatory is under discussion, led by the LPSC, in partnership with CNRS Physique and CNRS Terre & Univers. The objective is the addition of a new SAT focusing on the characterization and subtraction of galactic dust emissions that contaminate the cosmological signal, this new telescope would make it possible to fully exploit the observatory’s sensitivity to primordial gravitational waves.
“With the success of the Planck satellite mission, France has positioned itself as a leader in the science of the primordial Universe. Increased participation of our community in the observatory would make it possible to promote all of our expertise, whether instrumental or in data analysis,” adds Thibaut Louis, researcher at the IJCLab and head of the “Simons Observatory” master project at IN2P3.
About Simons Observatory
The Simons Observatory science team comes from the merger of two collaborations: the Atacama Cosmology Telescope and the Simons Array. In 2014, the mathematician and Simons Foundation co-founder Jim Simons has offered to fund this new collaboration. Extensions to the original project have been funded by the National Science Foundation (USA), and by research and innovation funds in the UK and Japan. The project has also received financial support from the founding universities: Princeton, Berkeley, San Diego, Chicago and Pennsylvania Universities. In total, the collaboration brings together more than 350 researchers from more than 35 institutions.
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