Astronomers are gearing up to cast the most acute gaze ever into the early universe. Nestled atop the 5,300-meter-high Cerro Toco in the Atacama Desert of northern Chile, the Simon Observatory is set to map the Cosmic Microwave Background (CMB) — also known as the afterglow of the Big Bang. With a sensitivity tenfold greater than its predecessor, the European Space Agency's "Planck" probe, this observatory is poised to become the new gold standard.
According to Nature, this $109.5 million observatory is slated for completion in a matter of weeks.
Jo Dunkley, a cosmologist at Princeton University and lead researcher for the observatory, stated, "This will be the best view of the CMB we've ever had."
One of the project's objectives is to search for traces of gravitational waves produced by the Big Bang within the CMB. This search aims to provide the first indisputable evidence of cosmic inflation, a brief period of exponential expansion thought to have occurred in the early universe. During this epoch, quantum fluctuations at microscopic scales are believed to have seeded the formation of large-scale structure in the universe.
This scientific collaboration is led by five U.S. universities and the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The project is named after mathematician and hedge fund investor Jim Simons and his wife Marilyn Simons. The Simons Foundation of the United States donated approximately $90 million towards the construction of the observatory.
Upon completion of construction, engineers will embark on a months-long process of fine-tuning and testing the observatory's instruments before fully engaging in its scientific mission.
The Simon Observatory consists of four telescopes, including three identical 0.4-meter Small Aperture Telescopes (SAT) and one 6-meter Large Aperture Telescope (LAT). Together, they will chart the subtle variations in temperature across different regions of the CMB, as well as its polarization — the preferred direction of oscillation of the electric field of the microwave radiation as it propagates through space.
The frontal view of the LAT receiver at the Simons Observatory, currently the largest receiver ever used for observing the Cosmic Microwave Background (CMB). Source: Mark Devlin/University of Pennsylvania.
Three SATs will be focused on covering 20% of the southern sky, aiming to study large-scale swirls in the polarization field of the CMB — regions spanning several times the apparent size of the Moon in the sky. It's in these regions where the cosmic inflation signal known as B-mode is expected to appear.
Marc Kamionkowski, a theoretical astrophysicist at Johns Hopkins University, explains that known quantum field physics suggests these features should be within the sensitivity range or close to it of the Simons Observatory. He was one of the first researchers to predict the existence of B-modes back in 1997.
While the SATs will focus on relatively smaller regions, the LAT will map 40% of the sky with finer resolution, recording both the temperature fluctuations and the polarization of the CMB. Scientists have been able to extract a wealth of information from the intensity of these temperature fluctuations and the area they span, leading to precise estimates of the age of the universe (13.8 billion years) and its composition (with only about 4% being ordinary matter).
LAT data can aid researchers in detecting signals of cosmic inflation in low-resolution polarization maps made by smaller telescopes. Mark Devlin, a cosmologist at the University of Pennsylvania and co-director of the observatory, emphasizes their importance in distinguishing false signals generated by Milky Way dust and other sources. The sensitivity of this experiment to polarization patterns will be six times greater than previous measurement efforts.
However, the quest for cosmic inflation signals is just one of the goals of this project; the research team plans to gain more scientific insights from the high-resolution CMB data obtained from the observatory. Researchers not only get a glimpse of the early universe but also study how its primordial radiation was affected during its 13.8-billion-year journey through space before reaching Earth.
The CMB gets lensed by the gravitational pull of large galaxy clusters and dark matter, a phenomenon known as gravitational lensing, which can be used to create 3D maps of these galaxy clusters. The Simons Observatory team will reconstruct the gravitational lensing of the CMB and determine how much of it is caused by cosmic neutrinos, enabling them to calculate the mass of these particles.
With the LAT repeatedly surveying the same areas of the sky throughout its lifetime, it can also track the movements of asteroids in the solar system and monitor active black holes at the centers of other galaxies, observing how they change over time. "We'll be able to track 20,000 or more active galactic nuclei, which we think are supermassive black holes with jets," Dunkley says.
The Simons Observatory will operate for two runs, each lasting about four years, with plans for a $53 million upgrade during its lifetime. The U.S. Department of Energy and the National Science Foundation will lead an even more ambitious project called CMB-S4 as a successor, set to begin observations in the mid-2030s.
