The science illuminated by the first light in the universe

The Advanced Simons Observatory will use the cosmic microwave background to help us understand the evolution of the universe and the many phenomena within it.

About 13.8 billion years ago, our universe ballooned outward at an incredible speed. Everything we observe today, which had been packed tightly together, expanded in a roiling mass of light and particles. It took 380,000 years for this hot, dense soup to thin and cool enough to allow light to travel through it. This first light, dating back to the formation of early atoms, is called the cosmic microwave background and can still be detected today.

Advanced Simons Observatory in Chile

The Simons Observatory in Chile, which will be renamed the Advanced Simons Observatory in line with upgrades to its detectors, data-sharing capabilities, and power supply. (Image credit: Debra Kellner)

“When you observe it, what you’re looking at are the initial conditions of the universe,” said Emmanuel Schaan, a staff scientist at SLAC National Accelerator Laboratory and a senior member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at SLAC and Stanford.

Schaan is one of many researchers collaborating on the Advanced Simons Observatory currently under construction in the Atacama Desert in Chile. The Simons Observatory is slated to come online later this year, but thanks to a recent grant from the National Science Foundation, its capabilities will continue to grow. The advanced version will include an additional 30,000 detectors for cosmic microwave background radiation, giving us a better picture of the early universe, its evolution, and many phenomena within it.

In addition to the detectors, the upgraded observatory will have improved data-sharing capabilities and a solar array that will provide 70% of the facility’s power, allowing for continuous, sustainable operation.

“It’s going to double the mapping speed of the Large Aperture Telescope Receiver and make our observatory phenomenally sensitive,” said Susan Clark, an assistant professor of physics at Stanford in the School of Humanities and Sciences and one of two project scientists for the Advanced Simons Observatory. “We’re going to have really deep, sensitive maps of the cosmic microwave background and the polarized dust emission from our galaxy, and also be able to see how the sky overhead changes from night to night.”

Detailed revelations

Often, surveys of large parts of the sky take years to collect and share data. But when it’s complete, the Advanced Simons Observatory will be able to make and analyze daily maps of the sky, sharing alerts with the larger scientific community about transient phenomena such as the bright flash of a tidal disruption event – when a star in a distant galaxy gets too close to a black hole and is ripped apart.

“Here’s a new way that we can observe the universe – watching the sky change in time in the millimeter-wavelength range of the electromagnetic spectrum. We’ve never been able to do that like this before,” said Clark, who is also a KIPAC senior member.

Schaan is particularly interested in using the new observatory to study how galaxies form. Because the cosmic microwave background has been traveling through space for nearly 14 billion years, it essentially provides a backlight for objects that were created more recently. Massive objects like galaxies and galaxy clusters cast shadows in the cosmic microwave background and their gravitational pull can bend photons around them, revealing otherwise invisible mass such as diffuse gases or dark matter.

“Around galaxies, there is an extremely extended halo of diffuse gas that is very hard to observe, and the Simons Observatory will allow us to reveal it,” said Schaan. “And by seeing how extended it is, we can fill in some of the major uncertainties about galaxy formation.”

Zeeshan Ahmed, a KIPAC senior member and lead scientist at SLAC, is an observational cosmologist working to understand how the universe evolved and why it looks the way it does. He hopes that data from the Advanced Simons Observatory will complement data from other observatories to paint a clearer picture of the universe and help resolve inconsistencies between the past and present.

“If you look at data from the early universe and the late universe, they’re very consistent except for a few jarring things that are not quite lined up,” said Ahmed. “Is this a fluke? Or is there something about fundamental physics that we haven’t yet discovered or understood?”

Built to surprise

Teams all over the country have been working to design and build different aspects of the telescopes, detectors, and data systems that will enable these observations. Ahmed and his colleagues, for example, have been designing the system that will convert the electrical signals from the detectors in the largest telescope of the Simons Observatory into data that can be shared and analyzed.

To detect cosmic microwave background photons, the sensors in the detectors must be kept at incredibly low temperatures – only a tenth of a degree above absolute zero (-459.49 degrees Fahrenheit). Even small variations from that temperature could throw off the readings, and the standard equipment to move and process those signals generates heat.

“We made some technological breakthroughs and came up with the architecture of how to connect the superconducting sensors out all the way to room temperature electronics without overloading the system with heat,” said Ahmed. “Simons Observatory will be the first major cosmic microwave background experiment to use this readout scheme at scale for scientific observation.”

The researchers have ideas about what they will find with the Advanced Simons Observatory. Beyond the cosmic microwave background, they will hunt for and study the birthplaces of distant stars, the contents of interstellar dust, exo-Oort clouds – spherical shells of ice and dust at the edges of solar systems – and a number of other phenomena. But, given the unique capabilities of this observatory, they are also open to finding something unexpected – encountering some puzzle piece in the universe that we didn’t know we were missing.

“When you’re able to look at the universe in some new way, you allow yourself the possibility of being surprised,” said Clark. “As long as humans have been around to wonder about things, we have tried to understand how we got here and how the universe works. And we are really at the frontier of our ability to do that.”