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Harvard Astrophysicists Confirm Existing Theories of Composition, Expansion of the Universe

The Harvard-Smithsonian Center for Astrophysics sits at 60 Garden Street, across the road from the Radcliffe Quadrangle.
The Harvard-Smithsonian Center for Astrophysics sits at 60 Garden Street, across the road from the Radcliffe Quadrangle. By Kathryn S. Kuhar
By Jeremiah C. Curran, Crimson Staff Writer

Researchers at the Harvard-Smithsonian Center for Astrophysics found that dark energy makes up two-thirds of the universe, according to a study published in a special issue of The Astrophysical Journal last month.

The study, which also found that one-third of the universe is composed of mostly dark matter, confirms existing theories about the configuration of the universe, said Dillon Brout, an Einstein Fellow at the Center for Astrophysics and lead author of the research papers.

“It puts on even stronger footing our understanding of the acceleration of the universe — just how much it is accelerating — and what kinds of theories that can explain that acceleration, the best theory being dark energy,” Brout said. “We’ve essentially doubled our ability to constrain dark energy and the acceleration of the universe compared to the next best analysis of this kind.”

The analysis looks at more than 1,500 stellar explosions called supernovae. It also reveals that the cosmos have likely expanded at an accelerating rate for billions of years.

“Our analysis is kind of like a dream team of the different people and collaborations that have been conducting these supernova surveys,” Brout added.

The researchers decided to examine supernovae that were the closest to Earth. Setting constraints on the distance and volume of space in which they would search for supernovae, they drew from data collected in the past 30 years.

“We also include datasets that go all the way out into more than three-quarters of the way back to the Big Bang,” Brout said. “Indiscriminate, systematic searches which are really good for understanding dark energy.”

The project grew out of an original analysis of 1,000 supernovae that Dan M. Scolnic, an assistant professor of physics at Duke University, published in 2018. The newer version expands the dataset and refines techniques for analyzing supernovae data.

“We’ve recalibrated all of the surveys that we’ve analyzed and that was a really large effort,” Brout explained.“It was basically redoing a lot of the work that these surveys had already done because there have been improvements in various aspects on how you can calibrate telescopes over the last 30 years.”

Brout is now considering exploring how the Hubble constant — the current rate of the expansion of the universe — interacts with his measurements of the cosmos.

“Why doesn’t our measurement agree with the measurement made in the early universe? That is one huge outstanding question,” he said. “We’re hoping that this analysis really sparks the community into helping find a solution, whether that’s astrophysics, whether that’s systematic errors in one of the analyses.”

“And then of course, there’s the possibility that our whole model of the universe is wrong — and that’s the most exciting one,” Brout added.
—Staff writer Jeremiah C. Curran can be reached at Follow him on Twitter @jerryccurran.

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