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March 28, 2001 Press Contact: Steve Koppes
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Scientific balloon adventure successfully concludes in Antarctica

Next up for Chicago astrophysicist: June 30 launch of NASA space probe

A University of Chicago experiment seeking new insights into the origin and evolution of the universe has come to a successful conclusion following a 27-day balloon journey high above Antarctica.

But even as Stephan Meyer begins to analyze the data from that experiment, he is helping to prepare a NASA space probe for launch June 30 that promises to produce even better results.

Scientists recovered the balloon experiment’s data tapes on Jan. 31 after landing their Twin Otter aircraft in remote west Antarctica between a rock field, two steep glacial slopes and a deadly crevasse.

“This balloon flight was certainly one heck of an adventure,” said Stephan Meyer, Professor in Astronomy & Astrophysics. “We’ve been successful and lucky. We’re happy with that.”

The experiment, called TopHat, was the first ever launched by the National Scientific Balloon Facility with a payload sitting on top of the balloon. TopHat scientists placed their one-meter telescope atop the balloon to get an unobstructed view of the sky.

“We have at least six days of data, which is roughly 20 times as much data as we normally get from a balloon flight. That’s the thing that’s going to make this whole operation so much fun,” said Meyer, who leads the international TopHat collaboration.

Working with Meyer are researchers at the Danish Space Research Institute, NASA’s Goddard Space Flight Center and the University of Wisconsin at Madison. The $2 million experiment is supported by grants from the National Science Foundation and the National Aeronautics and Space Administration.

TopHat’s telescope operates as a heat detector that records tiny temperature differences in the cosmic microwave background radiation, the big bang’s afterglow. The sun shines 24 hours a day during Antarctic summers, creating favorable conditions for long-duration balloon experiments.TopHat is the most recent in a series of astrophysics experiments that have heralded the era of precision cosmology, the study of the universe’s origin and evolution. As recently as the early 1960s, Meyer said, cosmology lacked a key element of science: the ability to make predictions that experiments could verify. “That’s totally changed. Now we’re in a situation where these are precision predictions and precision measurements.”

Some key predictions were made by the late David Schramm, a University of Chicago astrophysicist who died in 1997. Schramm’s calculations helped show that the element deuterium could be used to estimate how much of the universe consists of baryons–protons, neutrons and electrons, the building blocks of ordinary matter. His calculations further showed that only 5 percent of the universe consists of baryons.

Cosmic microwave background measurements permit astrophysicists to experimentally estimate the baryonic density of the universe. Last year an Antarctic balloon experiment called BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics), measured a baryonic density of approximately 7.5 percent. Another balloon experiment, called MAXIMA (Millimeter Anisotropy Experiment Imaging Array), measured a slightly lower baryonic value. And a ground-based experiment, the Cosmic Background Imager, came up with a still lower value.

“There are significant differences between the three experiments. The theoretical consequences for those differences is rather striking,” Meyer said. “The experiment with the first and perhaps the most precise answer, BOOMERANG, has the result that is most inconsistent with what people had thought was true before. That doesn’t make it wrong. It was just surprising.”

TopHat’s advantage over BOOMERANG is that it measures a much larger section of the sky–an important aspect of microwave background experiments–with approximately the same sensitivity. But the TopHat team will need approximately a year to analyze its results.

The next experiment that will produce microwave background results will be the University’s Degree Angular Scale Interferometer. DASI has been taking data from the South Pole for more than a year. The project leader, John Carlstrom, the Subramanyan Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics, has nearly completed his analysis.

“DASI should be able to narrow that error on the microwave background number and say, look, did Schramm get it right? Almost right?” said Michael Turner, the Bruce and Diana Rauner Distinguished Service Professor in Astronomy & Astrophysics. “I’m betting that the microwave background number is going to come down.”

The most definitive microwave background measurements will be made by the Microwave Anistropy Probe, which NASA has scheduled for launch June 30. Meyer is a member of the MAP science team.

“If everything turns out as the theorists expected, then we would basically be able to close the book on this aspect of cosmology,” Meyer said. “I fully expect there to be some surprises. I don’t know what they’ll be.”

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