Research done by the Atacama Cosmology Telescope (ACT) project produced the clearest and most accurate images of the universe’s infancy. For more than 10 years, Stony Brook University has been dedicated to researching such findings. Neelima Sehgal, an cosmologist and associate professor in the Department of Physics and Astronomy, is a key member of the ACT collaboration. Sehgal explained the inner workings of the ACT during her overview of the work done to unveil the images of the universe’s infancy.
“The [ACT] collaboration is a team of 160 people spanning 65 institutions, and is led out of Princeton [University] and the University of Pennsylvania,” Seghal said.
The ACT is located in the Atacama Desert, Chile, and has been collecting data for nearly 20 years. She said the telescope has been collecting microwave light data for the entirety of those years and is now off the mountain.
The images captured took place 380,000 years after the Big Bang occurred and are composed of the cosmic microwave background. According to the Big Bang Theory, the universe began with an infinitely small, hot and dense point, which rapidly expanded. The cosmic microwave background is the radiation from the aftermath of the Big Bang, otherwise known as the start of the universe.
“Throughout that process, we’ve had many data releases,” Seghal explained. She noted how she and her team have recently completed their final extensive data release.
Seghal said that these images became more precise as light was collected over time. She also noted that the ACT collaboration has been improving the telescope’s quality, contributing to the enhanced clarity of these images.
Seghal then explained how these images help detect what the earliest stages of the universe looked like.
“We’re getting a photograph of the universe from 380,000 years before the Big Bang because photons have traveled almost 14 billion years without hitting anything to come to us in our telescopes,” she said.
She said the light (cosmic microwave background) is considered a “baby picture” of the universe 380,000 years after the beginning of its formation.“We can’t see farther back than that because those photons never made it to us,” Seghal said. Photons represent the entire spectrum of electromagnetic radiation and are the smallest particles of light, which is why Seghal said, “it’s the oldest light in the universe.”
Suzanne Staggs, the director of ACT and the Henry DeWolf Smyth Professor of Physics at Princeton University, described the discovery as a way of identifying the earliest stars and galaxies.
“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,’ which was Europe’s first missions to study cosmic microwave background, and other earlier telescopes,” Staggs said.
In the press release, Jo Dunkley, the ACT analysis leader and the Joseph Henry Professor of Physics and Astrophysical Sciences at Princeton University, said, “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.”
Seghal and her team at Stony Brook have focused on the analysis of data collected by the telescope. She explained the most challenging part of this task for her and her team has been analyzing systematic effects that have developed as a result of the increased precision of the telescope.
“Over the past 20 years, we’ve been collecting more light, and all our error bars have been getting smaller and smaller. So every systematic effect could be an instrumental effect that could be biasing our results, or some kind of other signal in the sky that’s not the cosmic microwave background,” Seghal said.
She then mentioned emissions in the sky that may interfere with identifying cosmic microwave background.
“All of these things we’ve had to deal with more and more carefully to make sure that they’re not messing up the actual ‘baby picture’ image that we’re trying to get at,” Seghal stressed.
To overcome this challenge, Seghal and her team utilized a variety of research methods. She explained how they split up the data collected, as well as conducted null tests, which test for systematics (abnormal signaling that interferes with data).
She and her team also conducted blind analyses to overcome obstacles. “We don’t look at the final results, but we do all of these systematic checks, looking at differences, trying not to look at the actual signal [measurable light of the radiation], but just differences in the signal to check for systematic effects,” Seghal stated.
Seghal shared her amazement at how the research of these images has impacted students at Stony Brook, as well as the entirety of the Department of Physics and Astronomy.
“It’s just been amazing to see how much the field has progressed so fast over this arc of 20 years, and to know that there’s still so much more to come,” Seghal said. “It’s been pretty amazing to see the trajectory of the students that have grown up, myself included, starting as graduate students, but then even seeing my own students.”
